Climate change has transformed enormous swaths of protected woodlands in North Carolina into lifeless "ghost forests," a new study finds.

These ghost forests — marked by thousands of leafless, limbless trunks, stumps and toppled trees where healthy forests once stood — have taken over about 11% of the tree cover in North Carolina's Alligator River National Wildlife Refuge in the past three decades, the researchers found, resulting in tens of thousands of acres of dead greenery.

Die-offs like these are an expected effect of sea-level rise, which exposes more land to salty seawater, which literally sucks the moisture out of seeds and soil, the authors wrote. However, "it's not just the fringe that's getting wetter," lead study author Emily Ury, a biologist at Duke University in Durham, North Carolina, said in a statement.

Related: 6 Unexpected Effects of Climate Change

After analyzing thousands of NASA Landsat satellite images taken between 1985 and 2019, Ury and her colleagues calculated that more than 21,000 acres (8,500 hectares) of trees in the refuge were converted to ghost forests during that period. Remarkably, more than half of the newly killed forests stood more than 0.6 miles (1 kilometer) inland from the nearest coast, putting them far from the reach of rising tides.

A variety of factors led to the downfall of these inland forests — including hundreds of miles of drainage ditches that funneled seawater farther inland — but the storm surge that accompanied Hurricane Irene in 2011 proved to be the most devastating. During the surge, a 6-foot-tall (1.8 meters) wall of water gushed more than 1.2 miles (2 km) inland, flooding everything in its wake.

Alligator River National Wildlife Refuge was still recovering from a five-year drought when the hurricane hit, the researchers wrote, and the resulting damage was immense. In 2012 alone, more than 11,000 acres (4,400 hectares) of trees turned into "ghosts," far surpassing the 2,800 acres (1,100 hectares) of coastal land that was lost to sea-level rise during the entire 35-year period of the study. These vast new stands of drowned and dying trees were clearly visible from space, the researchers added.

As global sea levels rise in response to climate change, storm surges like Irene's are expected to become more destructive, and result in greater flooding. These surges are "the most pressing short-term problem regarding sea-level rise," Jacky Austermann, an assistant professor at Columbia University in New York, previously told Live Science. Lessons learned in North Carolina could help scientists predict and manage the damaging effects of future storm surges around the world, the study authors concluded.

Originally published on Live Science.

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The name "Irene" has been retired from the list of Atlantic Basin hurricane names, because of the damage Hurricane Irene caused when it hit the Caribbean and U.S. East Coast last year, the World Meteorological Organization announced today (April 13).

Storm names are decided on by the WMO and run on a seven-year cycle (so the list of names used in 2011 will be used again in 2017) in the Atlantic Basin and eastern North Pacific Basin, unless retired for causing a considerable amount of casualties or damage. Irene is the 76th hurricane name to be retired from the Atlantic list since 1954, according to a statement from the National Oceanic and Atmospheric Administration.

Irene will be replaced on the list with "Irma."

Irene became a hurricane on Aug. 22, 2011, and intensified to a Category 3 hurricane on the Saffir-Simpson scale of hurricane strength on Aug. 24 while positioned between Mayaguana and Grand Inagua in the Bahamas. It then gradually weakened and  made landfall in North Carolina on Aug. 27 as a Category 1 hurricane. Irene was the first hurricane to make landfall in the United States in three years.

Irene then drifted back out over the ocean and made a second landfall the following day near Atlantic City, N.J.  Later that day, the center of the storm, now much weakened, moved over Coney Island and Manhattan in New York.

Irene caused widespread damage, both in North Carolina and across the mid-Atlantic and Northeast as its rains caused catastrophic inland flooding in New Jersey, Massachusetts and Vermont.

Irene was directly responsible for five death in the Dominican Republic, three in Haiti, and 41 in the United States. For the United States, six deaths are attributed to storm surge/waves or rip currents, 15 to wind, including falling trees, and 21 to rainfall-induced floods, according to NOAA. 

Including flood losses, damage in the United States is estimated to be $15.8 billion. It was one of 14 billion-dollar disasters that hit the United States last year, a record number.

This story was provided by OurAmazingPlanet, a sister site to LiveScience. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

5 Categories

The Saffir-Simpson Hurricane Scale classifies storms into five categories based on their windspeed. The scale doesn't take into account rainfall or location, which means a Category 2 hurricane that hits a major city will probably inflict far more cumulative damage than a Category 4 hurricane that hits a rural area. The windspeed breakdown is as follows: Category 1: 74-95 mph (119-153 km/h) Category 2: 96-110 mph (154-177 km/h) Category 3: 111-130 mph (178-209 km/h) Category 4: 131-155 mph (210-249 km/h) Category 5: ? 156 mph (?250 km/h) Here are famous historical examples from each category.

Category 1: Danny (1985)

Danny formed when a tropical depression crossed Cuba into the Gulf of Mexico, where it rapidly intensified into a tropical storm and then a hurricane. It fell back to tropical storm status shortly after hitting shore.

Landfall: Lake Charles, Louisiana on August 15, 1985

Max. windspeed at landfall: 80 mph (129 km/h)

Impact: Danny produced an outbreak of 39 tornadoes and flash flooding across the Gulf Coast and Southeastern United States. It caused $100 million (1985 USD) of damage and three fatalities, two of them directly related to the storm. Danny quickly downgraded to a tropical storm as it crossed over onto land. [How Do Hurricanes End?]

Category 2: Erin (1995)

Formed from a tropical wave (a type of low-pressure atmospheric trough that moves east to west) that crossed the Atlantic from Africa, Erin's intensity grew as it passed from Jamaica up to Florida's Atlantic coast. It gained windspeed in the Gulf and struck the Florida panhandle and Georgia as a category 2 hurricane.

Landfall: Atlantic coast of Florida on Aug. 2, 1995 (as a Category 1) and the Florida panhandle on Aug. 3 (as a Category 2)

Max. windspeed at landfall: 100 mph (160 km/h)

Impact: In Jamaica, heavy rains caused a plane crash that killed five people. There were six drowning deaths along Florida shores. The total monetary damage from Erin was $700 million (1995 USD), primarily from downed trees, crop damages and ship damages. Erin caused NASA to halt some activities and preparation of shuttles at Kennedy Space Center. [How Are Hurricanes Named?]

Category 3: Katrina (2005)

Katrina formed over the Southeastern Bahamas and passed over land into the Gulf of Mexico. There it experienced unusually warm waters, and rapidly escalated to a category 5 hurricane before scaling down to a Category 3 upon hitting land.

Landfall: Category 3 hurricane with sustained winds of 125 mph (205 km/h) near Buras-Triumph, Louisiana on Aug. 28, 2005, then the Lousiana/Mississippi border with winds of 120 mph (193 km/h).

Impact: At least 1,836 people died in the actual hurricane and in the subsequent floods caused by the levee system breaking in New Orleans. This made it the deadliest U.S. hurricane since the 1928 Okeechobee hurricane; total property damage was estimated at $81 billion (2005 USD). [What If Hurricane Katrina Hit New Orleans Today?]

Category 4: The Great Galveston Hurricane (1900)

The storm's origins are unclear because of the limited observation ability at the beginning of the 20th century. Ship reports were the only reliable tool for observing hurricanes at sea. Based on those, the 1900 storm, like many powerful Atlantic hurricanes, is believed to have begun as a Cape Verde-type hurricanea tropical wave moving off the western coast of Africa.

Landfall: Galveston, TX, on September 8, 1900

Max. windspeed at landfall: 145 miles per hour (233 km/h)

Impact: The powerful winds and a 15-foot storm surge destroyed at least 3,500 homes and buildings and killed more than 8,000 people, making this hurricane one of the deadliest in history. Galveston residents did receive warnings about the coming storm from the U.S. Weather Bureau, but because satellites didn't exist, there was no way to predict its path ahead of time, and no one was certain it was really coming (and so people did little to prepare). [Why Do Hurricanes Curve Out to Sea?]

Category 5: Andrew (1992)

Andrew was the only major hurricane in the otherwise inactive 1992 hurricane season, but it was hugeone of only a handful of Category 5 storms ever to hit land. It formed from a tropical wave that moved off the coast of Africa, and intensified into a hurricane near the Bahamas. It passed over Southern Florida and into the Gulf, hitting landfall again in Lousiana.

Max. windspeed at landfall: 165 miles per hour (266 km/h)

Impact: Andrew caused $26.5 billion in damage (1992 USD, $41.5 billion 2011 USD), with most of that damage cost in south Florida, which it struck at Category 5 strength. Approximately 1 million people were evacuated from the area before the storm, so despite the tremendous destruction of property, only 54 people died. In the Florida Everglades, 70,000 acres of trees were knocked down by the storm. In addition, the storm killed approximately 182 million fish in the basin by increasing the turbidity of the water and lowering its oxygen level. [Why Are Category 5 Hurricanes So Rare?]

To say 2011 has been a wild weather year would be a huge understatement. From tornadoes to floods to wildfires, weather records were set across the United States this year, but not in a good way.

This year the United States had a dozen deadly weather events that each caused at least $1-billion in damage, the highest total of any year on record.

Most of the blame for the bad weather was pinned on La Niña, the cyclical system of trade winds that cools the waters of the equatorial Pacific (El Niño is La Niña's warm-water counterpart). La Niña can muck with global weather patterns, recurring every few years and lingering for as long as two years. This year's La Niña was one of the strongest on record.

"La Niña was running rampant during the first half of the year," said Henry Margusity, a senior meteorologist at AccuWeather.com. "Because of the strength of La Niña, it really got the weather juiced up for the big events we had."

There's rarely a smoking gun for bad weather, but as OurAmazingPlanet reported throughout 2011, La Niña was at least partly responsible for much of the year's awful weather.

"With a very strong La Niña like we saw, you got to be ready for the extremes," Margusity told OurAmazingPlanet.

Serious snow

La Niña took most of the blame for the big snows of this past winter. But La Niña did have help from another climate system gone awry. A naturally occurring, semi-periodic reversal of atmospheric pressure patterns and wind direction over the North Atlantic called the North Atlantic Oscillation, or NAO, was in a strong negative phase. That created a blocking pattern off the coast that kept the frigid air in place over the United States.

Large winter storms hit many central, eastern and northeastern states last winter. New York City and other parts of the Northeast got a winter blast just before the new year that caused trouble for flights for nearly a week. [Images: World's Snow Cover from Space]

Chicago was brought to a virtual standstill when 1-to-2 feet (0.3-to-0.6 meters) of snow fell across the city Feb. 2. The city's public schools canceled classes due to snow for the first time in 12 years. The storm caused more than $2-billion in damage and killed 36 people.

When all that snow finally melted, the water surged into the nation's riversand caused historic flooding. The Missouri and Souris rivers swelled beyond their banks across the Upper Midwest, and the Mississippi River saw record flooding farther south.

The wet weather didn't hit where it was most needed though. La Niña winters often see drier-than-normal conditions across the southern tier of the United States and this year saw a historic drought, coupled with devastating wildfires across Texas, Oklahoma and much of the Southwest. August 2011 was the hottest month in Texas's history, with an average temperature of 88.1 Fahrenheit (31.2 Celcius). June to August was also the state's driest summer on record, with only 2.44 inches (6.2 cm) of rain.

Terrible twisters

La Niña was also partly blamed for this year's terrible tornado season. Nearly 1,200 tornadoes struck the United States this year, according to the National Oceanic and Atmospheric Administration (NOAA). Four of these storms were rated at the highest tornado strength, an EF-5, with winds of over 200 mph (322 kph). The death toll from these tornadoes topped 500, a number not seen for a single tornado season since 1953.

But La Niña's blame comes more for what it didn't do during tornado season than what it did do.

La Niña began its exit in late winter, which allowed the jet stream to go rogue, driving winds into the heart of the United States where they violently mixed cool and warm air masses, creating the thunderstorms that spawned killer tornadoes.

The deadliest of 2011's tornado outbreaks struck the central and southern states from April 25-30. The outbreak led to 327 deaths. Of those, 240 occurred in Alabama. The deadliest of the estimated 305 tornadoes in the outbreak was an EF-5 that hit northern Alabama, killing 78 people.

One month later, an EF-5 tornado struck Joplin, Mo., killing at least 141 people, making it the deadliest single tornado to strike the United States since modern tornado record keeping began in 1950. [Tornado Damage Scale in Images]

Not all La Niña events are associated with highly active severe weather seasons, but some years with similar La Niña characteristics are also historic tornado years, including 1974, 1999 ? which saw an EF-5 tornado devastate Moore, Okla. ? and 2008.

This year's record snowpacks also aided the rouge jet stream because it kept the northern air cool, which made for violent mixing with the hotter-than-normal air to the south.

Horrible hurricanes

After tornado season, La Niña crashed, and has been struggling since. La Niña officially ended in early June, but re-emerged, albeit weaker, in early September. La Niña has been linked to increased hurricane activity in the Atlantic basin, and 2011 was an above average year.

The 2011 season saw 19 tropical storms, seven hurricanes and three major hurricanes — including the devastating Hurricane Irene, the only hurricane to strike the United States this year. Irene was the first hurricane to make landfall in the United States in three years. Its billion-dollar damage brought the United States back to the reality of hurricanes after years of quiet. Hurricane season runs from June 1 to Nov. 30.

Even after La Niña passes, its impacts can linger. La Niña can reduce wind shear, which is the contrast between wind speeds at the surface of the ocean and higher up in the atmosphere. Heavy wind shear can break up developing storms.

Low wind shear kept Irene alive for nine days in late August as it pummeled the East Coast. Warm waters in the Atlantic also fueled the storm.

What's in store for 2012?

Could we see a repeat of 2011's wild weather in 2012?

NOAA expects La Niña, which returned in August, to gradually strengthen and continue through the upcoming winter. That means the severe drought should continue though the winter. 

As for snow, some forecasters are worried about a blizzard striking the East Coast on Christmas this year, but Margusity isn't convinced because there is no blocking pattern in place right now.

It's too soon to predict the next hurricane season, and there is no pre-season tornado forecast, so forecasters will be keeping close watch on La Niña again in 2012.

You can follow OurAmazingPlanet staff writer Brett Israel on Twitter: @btisrael. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

The damage toll from this year's wild weather keeps growing. A June tornado outbreak and the wildfires that have plagued the Southwest were added to the year's list of U.S. billion-dollar weather disasters, bumping the 2011 total to a record 12, according to the National Oceanic and Atmospheric Administration (NOAA).

Earlier this year, Hurricane Irene had already put 2011 in first place by becoming the tenth billion-dollar weather disaster of the year, passing the $9-billion weather disasters of 2008.

These costly disasters don't hit the country evenly. Since 1980, wild weather has been costliest in the South. Texas, Oklahoma, Georgia, Alabama, Mississippi, Tennessee and North Carolina have had 33-to-42 billion-dollar weather disasters, according to NOAA.

Some eye-popping numbers about this year's wicked weather:

·       3-million residents lost power during an unseasonably early nor'easter storm Oct. 29-31.

·       343 tornadoes struck between Alabama and Virginia in late April, the largest outbreak on record.

·       199 tornadoes struck the Southeast on April 27, a record for a single day.

·       1-million acres in Texas were burned during this year's record wildfire season.

·       19 tropical storms formed in the Atlantic this year, the third-busiest season on record.

·       $3-billion will be needed to rebuild after a tornado struck Joplin, Mo., May 22, the single-costliest tornado in U.S. history.

·       300-percent-more precipitation than normal fell in the Ohio Valley, triggering historic flooding along the Mississippi River.

Here are the 12 U.S. billion-dollar disasters of 2011, which so far have combined to cause $200 billion in damage:

Texas, New Mexico, Arizona Wildfires, spring- fall:Continued drought and periods of extreme heat provided conditions favorable for a series of historic wildfires across the three states. The Bastrop Fire in Texas was the most-destructive fire in Texas history, destroying more than 1,500 homes. The Wallow Fire consumed over 500,000 acres in Arizona, making it the largest on record in Arizona. The Las Conchas Fire in New Mexico was also the state’s largest wildfire on record, scorching over 150,000 acres while threatening the Los Alamos National Laboratory. Over 3-million acres have burned across Texas this wildfire season. Total damage in Texas alone due to loss of property, timber and agriculture exceeds $750 million. Losses for wildfire activity across all three states exceeds $1 billion.

Midwest/Southeast Tornadoes and Severe Weather, June 18-22:  An estimated 81 tornadoes struck across Oklahoma, Texas, Kansas, Nebraska, Missouri, Iowa and Illinois. Additional wind and hail damage occurred across Tennessee, Georgia, North Carolina and South Carolina. The storms caused over $1 billion in insured losses and total losses greater than $1.3 billion.

Hurricane Irene, August 20-29: Irene first struck the United States as a Category 1 hurricane in eastern North Carolina, then moved northward along the Mid-Atlantic Coast. Wind damage in coastal North Carolina, Virginia and Maryland was moderate, with considerable damage resulting from falling trees and power lines. Irene made its final landfall as a tropical storm in the New York City area and dropped torrential rainfall in the Northeast that caused widespread flooding. More than 7 million homes and businesses lost power during the storm, and Irene caused at least 45 deaths and more than $7.3 billion in damages. [In Photos: Hurricane Irene]

Upper-Midwest flooding, summer: Melting of an above-average snowpack across the northern Rocky Mountains, combined with above-average precipitation, caused the Missouri and Souris rivers to swell beyond their banks across the Upper Midwest. An estimated 11,000 people were forced to evacuate Minot, N.D., due to the record-high level of the Souris River. Numerous levees were breached along the Missouri River, flooding thousands of acres of farmland. The flooding, which is ongoing, has caused more than $2 billion in damages.

Mississippi River flooding, spring-summer: Persistent rainfall nearly tripled the normal precipitation amounts in the Ohio Valley, and, combined with melting snowpack, caused historical flooding along the Mississippi River and its tributaries. The region suffered $2-billion-to-$4-billion in losses. [Mightiest Floods of the Mississippi River]

Southern Plains/Southwest drought, heat wave and wildfires, spring-summer: Drought, heat waves and wildfires scorched through Texas, Oklahoma, New Mexico, Arizona, southern Kansas, western Arkansas and Louisiana this year. In Texas and Oklahoma, respectively, 75 percent and 63 percent of range and pasture conditions were classified as "very poor" as of mid-August. Wildfire-fighting costs for the region are about $1 million per day. Well over $5 billion in damage has occurred so far, with over-2,000 homes and structures lost.

Midwest/Southeast tornadoes, May 22-27: Central and southern states saw approximately 180 twisters and 177 deaths within a week. A tornado rated EF-5 on the tornado-damage scale struck Joplin, Mo., resulting in at least 141 deaths, making it the deadliest single tornado to strike the United States since modern tornado record keeping began in 1950. The total losses were greater than $7 billion.

Southeast/Ohio Valley/Midwest tornadoes, April 25-30: This outbreak of tornadoes over central and southern states led to 327 deaths. Of those fatalities, 240 occurred in Alabama. The deadliest of the estimated 305 tornadoes in the outbreak was an EF-5 that hit northern Alabama, killing 78 people. Several major metropolitan areas were directly affected by strong tornadoes, including Tuscaloosa, Birmingham and Huntsville, in Alabama, and Chattanooga, Tenn. Total losses exceeded $9 billion.

Midwest/Southeast tornadoes, April 14-16: An outbreak over central and southern states produced an estimated 160 tornadoes. Despite the large overall number of tornadoes, few were classified as intense, with just 14 EF-3, and no EF-4 or EF-5, tornadoes identified. Total losses were greater than $2 billion. Thirty-eight people died, 22 of them in North Carolina.

Southeast/Midwest tornadoes, April 8-11: An outbreak of tornadoes over central and southern states saw an estimated 59 tornadoes. Total losses were greater than $2.2 billion.

Midwest/Southeast tornadoes, April 4-5: An outbreak of tornadoes over central and southern states saw an estimated 46 tornadoes. Total losses were greater than $2.3 billion. Nine people died.

Groundhog Day blizzard, Jan. 29-Feb. 3: A large winter storm hit many central, eastern and northeastern states. Chicago was brought to a virtual standstill when 1-to-2 feet (0.3-to-0.6 meters) of snow fell across the city. Total losses were greater than $2 billion. The snowstorm killed 36 people.

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Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

The 2011 Atlantic hurricane season was forecast to be a doozy and it delivered.

The season officially ends tomorrow (Nov. 30) and its legacy includes 19 tropical storms, seven hurricanes and three major hurricanes — including the devastating Hurricane Irene, the only hurricane to strike the United States this year. Irene was the first U.S.-land-falling hurricane in three years. Its billion-dollar damage brought the United States back to the reality of hurricanes after years of quiet.

"Irene reminded us that the Northeast can and does get hit byhurricanes," said Jeff Weber, an atmospheric scientist at the University Corporation for Atmospheric Research in Boulder, Colo.

Active trend

The 2011 season continued a trend of active hurricane seasons that began in 1995, according to the U.S. National Oceanic and Atmospheric Administration (NOAA). Tropical storms came in with the third-highest total, at 19 (tied with 1887, 1995 and 2010), since records began, in 1851. An average season has 11 tropical storms. [See a video of the season's storms.]

The seven hurricanes and three major hurricanes (Category 3 or higher on the Saffir-Simpson Hurricane Scale) that developed this year number only slightly above the averages of six and two, respectively.

The 2011 season affected the Mid-Atlantic more than the Gulf of Mexico. Hurricane Irene, the first hurricane to hit the United States since Ike hit Texas in 2008, socked the East Coast. The storm caused $7 billion in damage and became the worst tropical cyclone  to strike the Northeast since Hurricane Bob in 1991. Tropical cyclone is the generic term for tropical storms and hurricanes.

Irene inundated New York and Connecticut with water — up to 15 inches (38 centimeters) in some places. Irene was blamed for 46 deaths across 13 states.

As bad as the damage was, things could have been worse. Modern storm-tracking technology allowed NOAA forecasters to accurately map Irene's path for four days before its landfall Aug. 27, near Cape Lookout, N.C., allowing the population of the Outer Banks to evacuate. Irene was a major storm for a brief period, but it weakened to a Category 1 storm and so was not a major hurricane at landfall.

"We have now gone six years — since Wilma in 2005 — without a major hurricane making U.S. landfall," said Phil Klotzbach, an atmospheric scientist and hurricane forecaster at Colorado State University.

Few Gulf storms

Since 1878, when land-falling hurricane records begin, the 2006-2011 span is the longest stretch without a major hurricane hitting the United States, Klotzbach told OurAmazingPlanet.

While the East Coast was soaked by storms, the dearth of Gulf storms added tothe Texas drought.

One storm that did hit the Gulf was Tropical Storm Lee, which made landfall in central Louisiana. Lee spawned 38 tornadoes, the second most on record for a tropical storm. Most storms were turned away from the United States by an anomalous trough of low pressure along the East Coast, "which helped steer storms moving towards the U.S. coast back out to sea before they could make U.S. landfall," Klotzbach said.

You can follow OurAmazingPlanet staff writer Brett Israel on Twitter: @btisrael. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

Hurricanes are more likely to miss the United States when there is a huge swath of warm water in the Atlantic Ocean, reveals a new study of recent hurricane trends.

So far, this year's hurricane season has been an active one, with 16 named storms (which include tropical storms and hurricanes), five hurricanes and two major hurricanes (those Category 3 or stronger on the Saffir-Simpson scale).

Last year's hurricane season was even more active. With 12 hurricanes in the Atlantic,the season was one of the most active ever. But unless you live in the Caribbean, you probably did not notice. None of last year's hurricanes made landfall in the United States. And only one, Hurricane Irene, which roared along the East Coast, has so far made landfall this year. [Infographic: Storm Season! How, When & Where Hurricanes Form]

What boosted the U.S.'s luck?

Warm pool expansion

The new study found that a huge swath of warm water kept the 2010 hurricanes at bay. Warm water in the Gulf of Mexico, the Caribbean Sea and the western tropical North Atlantic, the so-called Atlantic warm pool, shifted to the east in 2010. That shifted hurricane creation further east in the Atlantic, making it more likely that steering currents in the atmosphere would make the storms curve away from the United States coast as they roared west.

In 2010, the warm pool was "very, very large," said study team member Chunzai Wang, an oceanographer with the U.S. National Oceanic and Atmospheric Administration (NOAA). In 2010, the pool was more than double its normal size.

The warm pool was so big that it blocked the effects of that year's La Niña. During La Niña years, cooler-than-average Pacific Ocean temperatures influence global weather patterns. La Niña years have been linked to active hurricane seasons.

"There's many factors that control the hurricane track," Wang told OurAmazingPlanet. "The Atlantic warm pool is only one of them. But In 2010, the warm pool played a major role."

About 25 percent of a season's hurricanes will typically hit the United States. That number falls by almost half in years with a swollen Atlantic warm pool, the new study found.

Like a leaf

The new finding may seem counterintuitive because warm ocean waters are what fuel big hurricanes, but the study doesn't contradict that bit of basic hurricane science. It's just that the warm waters not only feed a hurricane's fire, but they influence the atmosphere as well.

Wang said a hurricane behaves like a leaf floating in a river, totally at the whim of the current. So goes the river, so goes the leaf. A large Atlantic warm pool causes the atmospheric "river" to steer toward the northeast, carrying a hurricane with it.

"How the hurricanes go depends on the atmospheric steering flow pattern," Wang said.

The sample size for the study is small, since reliable hurricane records have only been kept since 1950 and more detailed satellite data only since 1970. Hurricanes are a complicated phenomenon, and there are many factors at play, Wang said, but at the very least, the study explains why no 2010 hurricanes hit the United States.

Just because a hurricane forms further to the east does not necessarily mean it has a strong chance of curving away from the East Coast, said atmospheric scientist Jeff Weber of the University Corporation for Atmospheric Research in Boulder, Colo. There are other atmospheric patterns in play, but they are not divorced from the Atlantic warm pool.

"I wouldsuggest that the [Atlantic warm pool] is a player in land falling East Coast hurricanes,but not the final word," Weber said.

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• Natural Disasters: Top 10 U.S. Threats

You can follow OurAmazingPlanet staff writer Brett Israel on Twitter: @btisrael. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

This Research in Action article was provided to LiveScience in partnership with the National Science Foundation.

Whimbrels, a type of small shorebird, are tough, skillful and canny fliers, routinely taking on non-stop migration flights of a few thousand miles.

A consortium of bird researchers from the College of William & Mary track their migrations — from high Arctic breeding grounds to wintering areas in South America and the Caribbean — by fitting the extreme fliers with lightweight, solar-powered transmitters.

The scientists have found that the considerable flight and navigation skills of whimbrels don't make them invulnerable. All four whimbrels currently being tracked successfully migrated through or around Hurricane Irene and Tropical Storm Maria, but two of them were gunned down by sport hunters on the Caribbean island of Guadeloupe.

Risking life and wing

The researchers discovered that the whimbrels routinely put themselves in harm's way. Bryan Watts, of the College of William & Mary, said that the southbound migration of the birds occurs during hurricane season and their routes usually take them over open ocean. The four tracked whimbrels came up against Hurricane Irene and all came out with scarcely a ruffled feather.

A bird that the researchers named Chinquapin flew unscathed through the most violent part of Hurricane Irene. A second bird, Goshen, also tangled with Irene, but only the outer bands of the storm. The remaining two, Hope and Machi, hunkered down on Virginia's Eastern Shore while Irene pelted down nearly a foot of rain.

Many whimbrels recharge their batteries in the Eastern Shore's marshes and tidal creeks before taking on the next leg in their migrations. Chinquapin opted for the direct flight, leaving upper Hudson Bay on Aug. 20. He flew right into Irene's northeast quadrant on Aug. 24 and days later, satellite signals showed him safe on the Bahamian island of Eleuthera.

Chinquapin got more than his 15 minutes of fame, written up in USA Today and featured by Diane Sawyer on ABC News. The other birds, Machi and Goshen, met different fates. Each was gunned down within hours of arriving on the Caribbean island of Guadeloupe.

Shooting swamps

Watts said sport-gunning for shorebirds from "shooting swamps" is legal and even traditional on many Caribbean islands that are not signatory to bird-protection agreements such as the Migratory Bird Treaty Act of 1918.

"The legal hunting there is just a holdover from the past," Watts said. "It's something that needs to be addressed. What happened to Machi and Goshen highlights this ongoing political issue."

The dead-bird count from legal shorebird hunts throughout the Caribbean is unknown. Watts pointed out that Machi and Goshen were the first tracked whimbrels to set down on Guadeloupe. The fact that both were killed within hours of their arrival suggests that the hunting pressure on the island is enormous, he said.

Following birds

Before their deaths, the birds contributed a great deal to our understanding of shorebird migration. Machi, for example, was tracked for over 27,000 miles back and forth between the Hudson Bay Lowlands of Canada and Brazil.

Following the birds' migrations has provided scientists with greater understanding of the importance of comparatively small areas — including the Eastern Shore — to the continued well-being of the species.

Scientists will continue to track the remaining members of the whimbrel quartet.

Editor's Note: Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. See the Research in Action archive.

The pageantry of fall may be particularly lovely in New England this year, and thanks in part to a source that has otherwise brought nothing but heartache to many in the Northeast: Hurricane Irene.

The massive storm, which swept across New England at the end of August, caused devastating flooding and millions of dollars of damage. But aside from knocking over individual trees, the hurricane left forests and wooded areas fairly intact.

"People were hit really hard," said Kevin T. Smith, a plant physiologist with the U.S. Department of Agriculture's Forest Service research station in Durham, N.H. "The storm was very serious for human infrastructure. People suffered more than the trees did."

One reason the region's trees escaped relatively unscathed, Smith said, is because the storm happened early enough in the season that leaves were still firmly attached, and able to hang on in spite of Irene's winds.

In addition, the storm dumped a huge amount of rain on the region — and moisture is one of the key ingredients required for a spectacular show as the seasons change. It helps leaves hang on to the trees, allowing for a longer-lived display.

"There's adequate soil moisture so the leaves may be able to continue functioning longer than if they were entering the fall period under dry conditions," Smith told OurAmazingPlanet.

Although the annual show of color is a visual treat for humans, it serves a very practical purpose.

As trees prepare for the onset of winter, they leech the sugars and nutrients from their leaves, in essence moving valuable sustenance to their protected insides so they can stay alive through the cold and dark of the coming season.

As nutrients are sucked out, the leaves gradually lose their rich green color, fading to the familiar fall colors of yellow and gold.

However, the rich reds on display in autumn are a different story. As summer wanes, some tree species manufacture a substance called anthocyanin, which helps them winterize. Anthocyanin is the same substance that lends red cabbage its purplish hue, and turns leaves crimson and scarlet.

In addition to moisture, temperature is also one of the drivers of fall color — specifically, variation in temperature, Smith said.

"Ideal conditions for bright displays would be sunny, warm days, and cold nights — it's that alternating that promotes the production of the anthocyanin pigment," he said.

Smith said that the leaves in his neck of the woods in New Hampshire have already begun to change, unrolling a tapestry of fall color.

"It's very pretty," Smith said, "and it's just beginning."

You can follow OurAmazingPlanet staff writer Andrea Mustain on Twitter: @andreamustain. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

After Hurricane Irene blew through the Bahamas, scientists raced to the islands on helicopters and ships to inspect the aftermath and learn more about how cyclones affect coastal areas.

On Aug. 25, the center of Hurricane Irene passed over the Exuma Sound and the Exuma Cays in the Bahamas. The tropical cyclone was a Category 3 storm at the time, with maximum sustained winds of 115 mph (185 kph).

Coincidentally, the University of Miami operates a field station in the Exumas. The location is interesting to scientists because the Exuma Cays have the only known examples of living stromatolites growing in the open sea.

"Stromatolites are reefs with a layered internal structure that were built by microbes rather than coral — they are Earth's first macro-fossils and dominated the Earth for 80 percent of the geologic record," said marine geologist Kelly Jackson at the University of Miami. "Photosynthesis by cyanobacteria forming these early microbial reefs generated the oxygen that allowed higher organisms — eventually including humans — to evolve."

In addition to studying stromatolites, researchers at the University of Miami are working in the Exumas to understand how changes in sea level over the past 500,000 years formed the islands and sculpted the coastal landscapes. To do so, they are mapping islands and shallow-water environments in conjunction with drilling into and extracting segments of rock to depths of 72 feet (22 meters) below present-day sea level. These cores act as a window into climates that existed in the past when the rocks were exposed at the surface.

All this expertise already in place in the Exumas gave researchers a unique chance to better analyze how hurricanes can affect coastal landscapes. Such knowledge "helps us understand possible effects from future storms so that coastal communities can better prepare before the storm comes," Jackson said. [Storm Targets: Where the Hurricanes Hit]

Also, this data helps scientists better understand the geological record and thus ancient history of the area, she added, since hurricanes would have had an impact on the islands long before humans began studying them.

Flying in after the storm

Just days following the storm, Jackson, along with marine biologist Kasey Cantwell and climatologist Roni Avissar, boarded a helicopter in Miami to inspect the geological impact of Hurricane Irene from the Exumas to the outer bands of the storm on Andros, Joulters Cays and Cat Cay. The objective was to take images of the affected areas to better understand the storm's impact on different types of terrain. The helicopter crew used three camera setups — one digital single-lens reflex (SLR) camera mounted on a gyroscope set up to automatically take two pictures every two seconds, two digital SLRs with a wide angle and telephoto lens to concentrate on specific details, and a high-definition camera for video.

"This was the first time I have flown in a helicopter for research in the Bahamas and it was amazing," Jackson said. "The helicopter has a lot of windows and while we were taking photos, the back door was removed to accommodate the camera mount system. We had breathtaking views of the beautiful Bahamian islands and shallow water environments."

They captured more than 23,000 aerial photographs of the islands, coastlines and shallow water environments in just nine hours, documenting the immediate changes from the storm, mostly from an altitude of 1,000 feet (305 meters). The helicopter ride "allowed us to assess the damage to a large area in a matter of hours — ground-based surveys of the Exuma Cays alone would have taken a minimum of a couple weeks to complete," Jackson said.

At about the same time, marine geologist Gregor Eberli at the University of Miami and a group of Brazilian scientists onboard the research vessel Coral Reef II recorded the effects of the storm from Bimini to Nassau. In addition to taking pictures of the hurricane's effects, they collected samples of sediment and seawater in Irene's wake.

"It was essential to do a survey as quickly as possible to understand changes caused by the storm and create a benchmark so we can also observe how long it will take the coastal system to return to normal," Eberli said. "We know from working in the Bahamas that the daily tidal fluctuations will eventually minimize the effects of the storm."

All in all, "while there have been previous geologic studies that have studied the effects of hurricanes on the coastal environments, this was the first assessment conducted so quickly after a storm over such a large area," Jackson said.

Irene's effects

Along the center path of the storm in the Exumas, the hurricane caused significant beach erosion. The storm surge also damaged vegetation, and in a few shallow-water environments along the 105-mile–long (170 kilometers), 3-to-6-mile–wide (5 to 10 km) island chain, the waters were cloudy with sediment. [Nature to the Rescue: Barriers to Storm Surge]

"It was sad to see the damage to homes, buildings, boats and docks, and we hope that the Bahamas can recover quickly from Hurricane Irene," Jackson said.

Despite this damage, there were no major changes to the coastal landscape overall. For example, major channels remain unchanged and are still accessible by boat.

"Many geoscientists think that hurricanes cause major changes to submarine environments — this and some previous studies show that this is actually not the case," Jackson said.

Away from the storm's center but within the area of storm-force winds, the Andros coastline and offshore reefs experienced very minimal damage. There were a few broken corals but overall no major damage to the ecosystem, the researchers noted.

"These effects will recover within months to a couple years," Jackson said. "There will not be any long-term negative effects to the coastal landscape."

The large sub-tidal shoals of Joulters Cay and Cat Cay remained unchanged, while at Joulters Cay, the storm surge formed a new beach ridge 4 feet (1.2 m) higher than the normal beach level. The storm surge flooded Andros Island and deposited a millimeter-thick layer of fine white mud on the mangroves and tidal flats, while the waters on the leeward side of Andros were milk-white even six days after the storm.

Understanding the impact

Cantwell and the Coral Reef Imaging Laboratory at the University of Miami are now processing the 23,000 aerial photographs and creating giant mosaics from them. These images will then be integrated with mapping software and previous satellite and aerial photograph data "so that we can truly understand the geologic impact of a Category 3 tropical cyclone on the islands and coastal system," Eberli said.

Such a combination of aerial photography, satellite imagery and mapping software "can be applied to storms, tsunamis, rising sea level, and essentially any situation where large-scale coastal monitoring is needed," Jackson said. "This is a major step forward for coastal scientists — in the past, these types of studies were limited because you did not have the ability to rapidly assess a large area, and therefore results were based mostly on particular sites but not a regional area. This will be the future of coastal studies."

And the team isn't done investigating Irene's impact yet.

"We will continue to work in this area for many years to come," Jackson added. "We will be able to see exactly how long it takes for the system to fully recover moving forward."

This story was provided by OurAmazingPlanet, a sister site to LiveScience.

Monster snowstorms were the big news of winter. The spring brought a deadly, record-setting tornado season and epic flooding. Not to be outdone, summer saw plenty of extreme weather of its own: hurricanes, heat waves, drought and wildfires.

With La Niña's return, the fall could be wild as well. Before the start of autumn this Friday (Sept. 23), here's a look back at the harsh summer that was.

Hurricane

When Hurricane Irene made landfall on North Carolina's Outer Banks, it became the first hurricane to hit the United States in nearly three years.

An active hurricane season has slowed down in recent days, but more storms are forecast for the late season in fall. So far there have been 14 named storms (which include tropical storms as well as hurricanes),three hurricanes and two major hurricanes (Irene and Katia).

Predictions had called for this season to be a doozy, with 14 to 19 named storms, seven to 10 hurricanes, and three to five major hurricanes (Category 3 or higher).

Irene came dangerously close to dealing a serious blow to New York City. It devastated New Jersey, upstate New York and Vermont with severe flooding. The storm became 2011's 10th billion-dollar weather disaster.

The summer's hurricane season also had several uncommon happenings. The leftovers of Hurricane Katia blew through Britain Sept. 12, an unusual occurrence that brought the strongest winds the United Kingdom has seen in nearly 15 years.

Canada also had some hurricane action. Hurricane Maria hit Newfoundland Sept. 16. Canada is hit by hurricanes more often than you'd think. More than a dozen have affected the Avalon Peninsula, where the province's capital, St. John's, is located, and where Maria hit.

Oppressive heat

Texas had the warmest summer for any state going back to 1895, according to the National Climatic Data Center. The state's average temperature was 86.8 degrees Fahrenheit (30.4 degrees Celsius). Neighboring Oklahoma and Louisiana had the second- and fourth-warmest summers of any state, respectively.

Wichita Falls, Texas, had 100 days of 100-degree Fahrenheit heat (38 degrees Celsius), a new state record. Dallas set its own city record for most 100-degree days in a year with 70.

The hot, hot heat wasn't limited to Texas. A July heat wave affected some 200 million people in the United States.

No state in the union was safe from the blistering heat that month, according to the National Climatic Data Center. Preliminary data showed 2,712 high-temperature records were tied or broken in July, compared with 1,444 last year, according to the NCDC. At least one weather station in all 50 states set or tied a daily high temperature record at some point during July.

Newark set an all-time high at 108 F (42.2 C) on July 22, breaking the 10-year-old record of 105 F (40.6 C). That same day in Washington, D.C., Dulles International Airport recorded its highest July temperature of all time, at 105 F (40.6 C).

Drought

As if the heat wasn't bad enough, the Southwest received no rainfall to speak of. June to August was the driest summer on record in Texas, with only 2.44 inches of precipitation falling on average.

Texas' current drought is the most severe one-year drought on record, according to Texas State Climatologist John Nielsen-Gammon of Texas A&M University. Levels of extreme (81 percent) and exceptional (14 percent) drought in Texas affected 95 percent of the state's area, according to the Drought Monitor at the University of Nebraska-Lincoln.

The drought hasn't been confined to Texas. Nearly one-fifth of the contiguous United States is in the grip of extreme drought.

Wildfires

The hot and dry weather created dangerous fire conditions. Nearly 18,612 wildfires have burned 3.5 million acres of Texas so far this year, according to the Texas Forest Service. That's about the size of Connecticut.

Six of the state's 10 largest wildfires came during 2011. The damage was estimated at more than $5 billion.

Flooding

While the Southwest continued its arid streak, the Upper Midwest continued to see severe flooding.

Melting of an above-average snowpack across the northern Rocky Mountains, combined with above-average precipitation, caused the Missouri and Souris rivers to swell beyond their banks across the Upper Midwest.

An estimated 11,000 people were forced to evacuate Minot, N.D., due to the record high level of the Souris River. Numerous levees were breached along the Missouri River, flooding thousands of acres of farmland. The flooding, which is ongoing, has caused more than $2 billion in damages.

The Mississippi River flooding of the spring also spilled into summer.  Persistent rainfall (nearly triple the normal precipitation amounts in the Ohio Valley), combined with melting snowpack, caused historical flooding along the Mississippi and its tributaries. The region suffered $2 billion to $4 billion in losses. At least two people died.

Cold

The summer also saw a couple of odd cold records. The temperature in the "Nation's Icebox," International Falls, Minn., dipped to 19 F (minus 7 C) on Sept. 15, the town's first-ever temperature in the teens for the month of September, according to the National Weather Service. [Related: The Coldest Places on Earth]

s the summer in Canada neared its end, Edmonton, Alberta, finally saw its last pile of snow melt. The last holdout drift was a patch of snow at Edmonton's west end snowstorage facility, where plows dump snow scooped from city streets. The last snowflake finally melted late in the afternoon of Sept. 10.

• The World's Weirdest Weather
• The Most Extreme Environments on Earth
• Weirdo Weather: 7 Rare Weather Events

Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

When Hurricane Irene barreled up the U.S. Eastern coastline, the storm left behind a path of widespread damage — and a generous helping of mysterious, squishy gray blobs in shallow waters and beaches from Virginia to New York, according to news reports.

"They’re pretty disgusting looking," Cathy Hopkins of Hampton, Va., told local media outlet the Daily Press.

Hopkins spotted dozens of the nasty floating blobs — many of which give off a powerful stench — near the mouth of the Poquoson River, off the Chesapeake Bay.

So what are these strange invaders?

"They're potato sponges," said Emmett Duffy, a professor at the Virginia Institute of Marine Science, in a statement.

The institution has been inundated with queries about the blobs, which have been described as being of "various sizes," with the smallest "around the size of a baseball." Reports of their texture range from "kind of rubbery or leathery" to "kind of soft."

Unlike their tuber namesakes, potato sponges are animals. The simple invertebrates usually remain out of sight beneath the waves, anchored to the seafloor. The unobtrusive filter-feeders, which can grow to the size of a soccer ball, inhabit shallow coastal habitats around the world.

Stormy weather can churn up the ocean waters where potato sponges dwell, dislodging them from the seafloor and unleashing a flood of dying or dead sponges — hence the foul smells — onto an unsuspecting coastal population.

Although a plague of sponges doesn't always follow a big storm, it has happened in the past. Hundreds washed ashore in Virginia after Tropical Storm Hanna in 2008, the Daily Press reported.

El Niño may get a bad wrap for bringing wild weather, but hurricane season during an El Niño year isn't much to fear, according to a new study. Scientists found that tropical cyclones that form during an El Niño year are more likely to curve harmlessly away from land.

Scientists at the University of Miami discovered the "intriguing relationship" between hurricane tracks and climate variability by studying data on hurricane tracks from the Atlantic gathered between 1950 and 2010.

In the study, storms were classified into three different categories based on their projected paths: straight moving, re-curving landfall or re-curving ocean. Storms that develop farther south and/or west in the tropical Atlantic are more likely to become straight-moving storms that ultimately affect the Gulf Coast of the United States and the Western Caribbean. However, storms that form more north or east have a greater chance of curving northward and threatening the Eastern Seaboard or simply curving into the open ocean. [Infographic: Storm Season! How, When & Where Hurricanes Form]

The study found that El Niño seasons were associated with fewer storms overall, and that the storms that did form were less likely to make landfall due to changes in the atmospheric steering currents, which guide the overall movement of storms. El Niño is where waters over the eastern Pacific Ocean are warmer than normal.

The 2009 hurricane season was the least active in 12 years and the lack of activity was blamed on El Niño. That season saw nine tropical storms, three hurricanes and two major hurricanes. An average Atlantic season produces 11 named storms, six hurricanes and two major hurricanes. Of the 2009 storms, only Tropical Storm Claudette made landfall in the United States.

"In a typical El Niño season, we found that storms have a higher probability of curving back out into the ocean as opposed to threatening to make landfall along the East Coast of the U.S. due to a change in the circulation across the Atlantic," said study team member Angela Colbert. "This is important for not only weather forecasting, but insurance companies, who can use these findings when determining seasonal and yearly quote rates."

La Niña seasons, when the equatorial Pacific Ocean surface is cooler than normal, are associated with both greater numbers of storms as well as an increased likelihood that they will make landfall. Last year was an active year in the Atlantic basin, due to a moderate La Niña, with 19 named storms, 12 hurricanes and 5 major hurricanes. None of the hurricanes made landfall in the United States.

The 2011 Atlantic hurricane season is at its peak, and La Niña is predicted to re-emerge after dying down over the summer. The season was forecast to be active and has lived up to that prediction so far with 14 named storms, two hurricanes, both of which became major hurricanes, and one of which, Irene, made landfall along the East Coast.

• History of Destruction: 8 Great Hurricanes
• Hurricanes from Above: See Nature's Biggest Storms
• Weirdo Weather: 7 Rare Weather Events

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Hurricane Irene caused billions of dollars in damage and forced millions of people to evacuate, which could force the name "Irene" into retirement even though the storm was only a Category 1 when it made landfall and was downgraded to a tropical storm as it ravaged the Northeast.

Hurricane name retirement decisions are made by high-level committees, which take months to decide, so it's still too early to know if the name "Irene" will be retired.

In the Atlantic basin, tropical cyclone names (which include tropical storms and hurricanes)are retired, never to be used again, if the storm causes noteworthy destruction, according to the National Hurricane Center.

Retiring a storm name helps prevent confusion between a new storm with a historic, well-known one.

Irene's fierce winds and relentless rains are likely to make the storm the latest billion-dollar natural disaster of 2011.

"Although Irene never reached the highest category levels of intensity, it did cause enough havoc to at least merit consideration," said atmospheric scientist Eugene McCaul of NASA's Marshall Space Flight Center.

Jeff Weber, an atmospheric scientist at the University Corporation for Atmospheric Research in Boulder, Colo., agreed that retirement is a possibility.

"Usually it takes a 5 to retire, but societal and economic impacts are also factors, somaybe," Weber said, referring to Category 5 storms, the highest level of the Saffir-Simpson scale of Hurricane Strength

Recently retired hurricane names include Charley ­­(2004), Dennis (2005), Dean (2007), Fabian (2003), Frances (2004), Felix (2007), Gustav (2008), Iris (2001), Isidore (2002), Isabel (2003), Ivan (2004), Ike (2008), Igor (2010), Juan (2003), Jeanne (2004), Katrina (2005), Lili (2002), Michelle (2001), Noel (2007), Paloma (2008), Rita (2005), Stan (2005), Tomas (2010) and Wilma (2005).

• History of Destruction: 8 Great Hurricanes
• Infographic: Storm Season! How, When & Where Hurricanes Form
• Storm Targets: Where the Hurricanes Hit

Email OurAmazingPlanet staff writer Brett Israel at bisrael@techmedianetwork.com. Follow him on Twitter @btisrael.

New York City largely dodged a bullet as Hurricane Irene did relatively little damage to the city. The same can't be said for areas further inland, such as Vermont and upstate New York, which are battling historic flooding.

In New York City, where transit was shut down citywide and coastal residents were evacuated for the first time ever, the storm surge pushed water onto low-lying areas and trees were felled — far from a worst-case scenario.

Just before the storm hit the city, it weakened and accelerated northeast. Irene was a tropical storm by the time it made landfall with the relatively calmer parts of the storm passing over the city. But New York City wasn't the only place in Irene's path. Towns all around the Big Apple show what might have been.

Rains and flooding

From North Carolina to Vermont, Irene killed at least 27 people, forced 2.4 million people to evacuate and caused billions of dollars in damage, according to news reports. The big problem was not hurricane strength winds, but heavy rains and massive flooding.

"Irene did about what was expected from the forecasts," said atmospheric scientist Eugene McCaul, of NASA's Marshall Space Flight Center in Huntsville, Ala. "The rainfall was probably the biggest threat, partly because most ofthe East and New England have had a very wet August even before Irene's onslaught."

Flooding in Lodi, N.J., was caused by Irene dumping torrential rains on already saturated soils. According to the New Jersey State Climatologist, some places in the state received half their yearly rainfall in August alone, reported Climate Central.

Flooding is still ongoing in upstate New York; some rivers have not having yet crested, and tens of thousands are without power, reported WNYC.

"What happened in the mid-Hudson and the Catskills was the higher bands of rain hit New York," said Gov. Andrew Cuomo in a press conference today (Aug. 29). Irene's massive size, hundreds of miles wide, and slow velocity, inundated the state for nearly a full day.

Major damage

Irene dumped six to 10 inches (15 to 25 centimeters) of rain across New England. Nearly every major Vermont highway was damaged from Irene's heavy rains, reported Vermont Public Radio. The flooding is the worst for that state in 73 years, according to the Weather Channel. Four to six of the state's famous covered bridges were destroyed, according to Vermont's Emergency Management Department. [In Photos: Hurricane Irene's Fury]

One contributor to Vermont's extreme floods is also one of the state's iconic attractions: mountains. Higher rates of rain fall there, which is then channeled into valleys, agitates rivers that aren't ready for the gush of water, said Jeff Weber, an atmospheric scientist at the University Corporation of Atmospheric Research, in Boulder, Colo.

"Mountainous terrain always exacerbates flooding for both those reasons," Weber told OurAmazingPlanet.

New York City, at least, can breathe a sigh of relief. The outcome of the storm could have been very different.

• History of Destruction: 8 Great Hurricanes
• Infographic: Storm Season! How, When & Where Hurricanes Form
• Storm Targets: Where the Hurricanes Hit

Irene may be nothing more than a remnant low-pressure system over Arctic waters, but hurricane season is far from over. Tropical Depression 12 has formed in the eastern Atlantic and is poised to become Hurricane Katia, with a track taking it toward the Caribbean.

Communities along the Eastern Seaboard are cleaning up from Irene's fierce winds and relentless rains , which caused major flooding in many areas. Meanwhile, out over the Atlantic Ocean, the atmosphere is continuing to churn up more storms.

The remnants of Tropical Storm Jose, which formed over the weekend, are dissipating south of Nova Scotia, and now Tropical Depression 12 has formed off the west coast of Africa.

This new tropical system is about 405 miles (650 kilometers) south-southwest of the southernmost Cape Verde Islands and has winds of 35 mph (55 kph), according to the most recent advisory from the National Hurricane Center.

The budding storm is expected to blossom into a tropical storm, possibly as early as tonight, and eventually into a hurricane. When it becomes a tropical storm, it will be given the name Katia, the name that replaced Katrina after it was retired for the massive devastation it wrought on New Orleans and the Gulf Coast. [See satellite images of Katrina's aftermath .]

Currently, Tropical Depression 12 is not a threat to any land, and isn't expected to pose one for at least the next five days. Over this period, though, the system is projected to possibly strengthen into a Category 2 hurricane.

Whether or not the future Katia has an impact on the Caribbean will depend on other patterns in the atmosphere, as these can alter the path of a hurricane some storms continue straight on, while others curve back out to sea.

If and when Katia does become a hurricane, it will be the second of the 2011 Atlantic season (Irene was the first), which has been projected to be a doozy. The National Oceanic and Atmospheric Administration updated its forecast on Aug. 4, predicting 14 to 19 named storms (which include tropical storms and hurricanes), seven to 10 hurricanes and three to five major hurricanes. An average Atlantic hurricane season will see 11 named storms, six hurricanes and two major hurricanes. August through October are the peak months of the Atlantic hurricane season.

• History of Destruction: 8 Great Hurricanes
• Infographic: Storm Season! How, When & Where Hurricanes Form
• Storm Targets: Where the Hurricanes Hit

As Hurricane Irene was bearing down on the East Coast late last week, many commentators warned of its destructive potential by invoking the memory of Hurricane Katrina.

Hurricane Katrina slammed into the Gulf Coast six years ago today (Aug. 29), flooding nearly all of New Orleans in the process. The storm remains a potent cultural touchstone, serving as a reminder of nature's power — and the importance of planning properly for worst-case scenarios.

Since Irene made landfall and was downgraded to a tropical storm over the weekend, we can begin to take its measure a little better. So how does Irene compare to Katrina?

Birth date and place

Irene: Meteorologists gave Irene its name Aug. 20. At that point, it was a tropical storm about 190 miles (306 kilometers) east of the Caribbean island of Dominica. In the early hours of Aug. 22, Irene graduated, becoming the first hurricane of the 2011 Atlantic season.

Katrina: Katrina was named Aug. 24, 2005, when it was a tropical storm about 65 miles (105 km) east-southeast of Nassau in the Bahamas. Katrina became the fifth hurricane of the 2005 Atlantic season when it was upgraded the next day.

Storm path

Irene: Irene made landfall in Puerto Rico in the early morning of Aug. 22, then continued to move northwest. As it neared the U.S. East Coast, Irene banked heavily north, churning toward another landfall in North Carolina.

The storm came aground at that state's Cape Lookout around 7:30 a.m. EDT Saturday (Aug. 28). Irene then kept moving northward in near-shore waters, hitting New York City around 9 a.m. EDT Sunday (Aug. 28) and New England a few hours later.

Katrina: Katrina took a completely different route. The hurricane made landfall in southeast Florida on Aug. 25, then popped out into the Gulf of Mexico to the west. It churned westward through the Gulf for a while, gaining strength from the warm waters, then arced northward.

Katrina made its Gulf landfall on the morning of Aug. 29 near Buras, La., about 50 miles (80 km) southeast of New Orleans. The storm kept weakening as it moved north, finally dying out around the Great Lakes region Aug. 31. [In Photos: Gulf Coast Damage from Hurricane Katrina]

Size

Irene: Irene's mammoth size made many forecasters nervous, as the storm had the potential to pummel huge swaths of the Eastern Seaboard with heavy rain, flooding and strong winds. At its largest, Irene measured about 600 miles (966 km) across, nearly as big as Texas.

Katrina: The 2005 storm was also enormous, though apparently not quite as big as Irene. Katrina was about 400 miles (644 km) wide when it made landfall in Louisiana.

For what it's worth, the biggest hurricane ever recorded was Typhoon Tip. (Hurricanes in the western Pacific Ocean are called typhoons.) The 1979 storm, which made landfall in southern Japan, was nearly 1,400 miles (2,253 km) wide at one point. That's almost half the size of the continental United States. [Hurricanes from Above: See Nature's Biggest Storms]

Intensity

Irene: Irene was a big, bad storm, but it could have been worse. The hurricane maxed out at Category 3, meaning its highest sustained wind speeds never topped 130 mph (209 kph). And Irene was not that powerful when it hit populated areas.

Irene was still just a tropical storm, for example, when it passed over Puerto Rico. It was a Category 1 hurricane when it hit North Carolina, with maximum sustained wind speeds around 85 mph (137 kph). By the time it hit the Northeast, Irene had weakened to a tropical storm again, with top winds of about 60 mph (97 kph).

Katrina: While Hurricane Irene covered more area, Katrina was more intense. In the Gulf of Mexico, Katrina grew into a Category 5 hurricane — the strongest storm there is. Katrina's maximum sustained winds reached speeds of around 173 mph (278 kph).

But Katrina weakened as well before making landfall. When it hit Louisiana, the storm had been downgraded to a Category 3 hurricane and boasted max wind speeds around 127 mph (204 kph).

Death and destruction

Irene: While it's far too early to fully gauge Irene's impact, it's already clear the storm is far from another Katrina.

Irene's storm surge likely maxed out around 4 to 8 feet (1.2 to 2.4 meters) along the East Coast, and it drenched huge swaths of land with heavy rain. As a result, many areas have suffered serious flooding, meaning Irene's economic toll will be considerable. Some experts say it is likely to be the 10th of the billion-dollar weather disasters of 2011.

However, the destruction is nowhere near that of Katrina's. As of Sunday morning, news reports pegged Irene's cumulative death toll at 10 or so — not even close to the human toll Katrina exacted.

Katrina: Katrina was an epic disaster. The hurricane flattened and flooded much of coastal Alabama, Mississippi and Louisiana, generating storm surges of nearly 28 feet (8.5 meters) in some places.

Some experts estimate Katrina caused $125 billion in damage, making it the costliest natural disaster in U.S. history. And the storm killed more than 1,800 people, the vast majority of them in Louisiana. Many of these people died after New Orleans' levee system failed and most of the city was flooded.

Getting out of the way

Irene: In general, most East Coast communities took Irene very seriously and started taking measures early. New York Mayor Michael Bloomberg, for example, issued a mandatory evacuation order for low-lying areas of the city at 2 p.m. EDT Friday (Aug. 26), nearly 48 hours before the hurricane hit the Big Apple.

Other population centers along the coast were similarly cautious, and millions of people were told with plenty of time to spare to get out of Irene's path.

Katrina: New Orleans Mayor Ray Nagin issued a voluntary evacuation order on the evening of Aug. 27, 2005. As the storm bore down on his city, the mayor upped that to a mandatory order around 11 a.m. the next day — about 18 hours before the storm hit.

The vast majority of New Orleans residents got out of harm's way. But some who were less mobile — seniors, disabled people and those without cars, for example — were left behind, and many of them died. Six years later, who should bear the brunt of blame for this evacuation failure is still being debated.

This SPACE.com story was provided by OurAmazingPlanet, a sister site to LiveScience. You can follow Mike Wall, senior writer for SPACE.com, on Twitter: @michaeldwall.

NEW YORK — Hurricane Irene battered the East Coast this weekend, blasting buildings and trees that hadn't felt such strong winds in decades, and flooding subways, tunnels and entire coastal neighborhoods.

Thankfully, Irene diminished in strength before making landfall on the Mid-Atlantic Coast and New England; though she is estimated to have caused $7 billion in damages, things could have been a lot worse. And atmospheric scientists say they will be.

They warn that hurricanes will get more destructive in the future. And as oceans warm, more and more of the strongest storms will creep north.

Warm seas

About 90 tropical cyclones form worldwide each year; that pace hasn't changed recently. Rather than causing more hurricanes and typhoons to develop, the 0.5-degree Celsius rise in tropical sea surface temperatures that has occurred over the past 30 years seems to have another effect. As Colorado State atmospheric scientist James Elsner ominously put it: "The strongest storms are getting stronger."

Hurricanes are like heat engines, Elsner explained. When the ocean puts more heat in, more energy comes out in the form of faster winds that blow for longer. As detailed in a 2008 paper in Nature (and in later studies analyzing subsequent hurricane seasons), he and his colleagues have noticed a steady upward trend in the maximum wind speed of the strongest hurricanes. For the top fifth most intense hurricanes, wind speeds have increased by 4.5 miles per hour per degree-Celsius rise in the ocean temperature. For storms in the top 10th of the intensity ranking, wind speeds have increased by 14.5 mph per degree Celsius.

That's a jump of almost an entire category on the Saffir-Simpson Hurricane Scale that rates hurricane intensity. [Are Category 6 Hurricanes Coming Soon?]

Only the strongest tropical storms seem to be affected by rising ocean temperatures; Elsner says this is because they alone experience a "thermodynamic perfect environment" — open waters with no wind shear coming from land. "Most storms are struggling as they pass near the coast. Only strong storms in this favorable thermodynamic environment are able to intensify with the warm ocean," he told Life's Little Mysteries.

Theoretical models for how ocean temperatures should affect hurricane intensity square with Elsner's real-world data. Kerry Emanuel, a professor of meteorology at MIT and an expert on hurricane intensification, has developed a model called the "maximum potential intensity theory," which predicts that the strongest storms will get stronger as seas warm.

The effect seems especially apparent in the North Atlantic, where cooler waters used to knock the wind out of hurricanes as they moved north, but no longer do.

Emanuel first presented his model in a 2005 article in Nature. "The correlations between Atlantic hurricane power and sea surface temperature have actually improved [since then]," he wrote in an email. This strengthens the predictions laid out in his theory. He regularly updates maps displaying the maximum cyclone intensity throughout the world's oceans.

Controversy

Not everyone is convinced that the growing intensity of hurricanes results from global warming.

Tony Barnston, the lead forecaster at the International Research Institute for Climate and Society, said there are more factors than just ocean temperature involved in making storms stronger.

"So far, the ocean temperatures have not increased by a sufficient amount to make an obviously higher observed hurricane activity level," he told us. A climate cycle called the Atlantic Multi-decadal Oscillation may explain the seeming surge in hurricane activity over the past 15 to 20 years, he said. Ultimately, more study — or time — is needed before the impact of higher ocean temperatures will become apparent.

David Easterling, chief of the Global Climate Applications Division at the National Oceanic and Atmospheric Administration, thinks that both man-made climate change and natural climate cycles are playing roles.

"Certainly, ocean temperatures in the tropical regions have an impact. But the effect of climate change might be superimposed onto the Atlantic Multi-decadal Oscillations. Hurricanes are very complicated storms that are impacted by a lot of different things," he said. [Tornadoes, Floods, Hurricanes: Is All the Wild Weather Connected?]

Either way, the scientists we contacted all agree: Global warming will make hurricanes more destructive.

Surf's up

"Sea level rise is generally accepted," Barnston wrote in an email. The physical explanation is straightforward: Warmer air is melting the glaciers, so there's more water. Observations have shown that the ocean is rising by 0.12 inches per year, and rising at a faster rate all the time.

One model by Vivien Gornitz of NASA's Goddard Institute for Space Studies and colleagues predicts that the sea level around New York City could jump 15 to 19 inches by 2050 and by more than 3 feet by 2080. When it comes to hurricane impacts, Barnston said the consequence of a higher sea level is also straightforward.

"With a higher 'normal' sea level, the sea level during a hurricane would cause more severe flooding, since the normal sea level would already be higher than it was in the past," Barnston wrote. Hurricanes can cause enormous storm surges, pushing 30-foot-tall walls of water in front of them.

"If the tides are higher on the coasts, then your mitigation efforts, such as seawalls, will not be designed for the storms of tomorrow," Elsner said.

Coping mechanisms

The researchers also agreed that Atlantic and Gulf Coast cities need to improve their hurricane plans, regardless of the fact that storms may get worse.

Barnston thinks coastal cities should discourage development along low-lying areas. "The worst need is not to build new homes or businesses at very low elevations anymore, such as anything below 6 feet elevation above current sea level," he wrote.

Hurricanes have always been extremely dangerous, and people have always tended to underprepare for them, Easterling said. "Hurricanes are not something you want to mess around with. Standards and that sort of thing need to be updated, and need to be looked at regularly, especially in developments and infrastructure along the coast. People need to review their hurricane plans, and cities need to have evacuation routes set up."

He, too, believes people need to stop building in low-lying coastal areas. "But of course, there are always people willing to take that risk."

After all, a house by the sea is the most peaceful place in the world — most of the time.

This story was provided by Life's Little Mysteries, a sister site to LiveScience.

Satellites caught this view of Irene just 28 minutes before it made landfall in New York City as a strong tropical storm.

The GOES-13 took this image of Hurricane Irene at 8:32 a.m. EDT today (Aug. 28). The image showed Irene's huge cloud cover blanketing New England, New York and over Toronto, Canada. Shadows in Irene's clouds indicate the bands of thunderstorms that surround Irene.

Flooding occurred in coastal and riverside areas of the city, and downed trees were reported in many spots around the city. Overall, though, Irene was not the worst case scenario it could have been for New York City.

The storm did still cause considerable damage all along the Eastern Seaboard and will surely become the 10th billion-dollar weather disaster for the United States in 2011.

The center of the storm was about 10 miles (20 kilometers) west of Danbury, Conn., and is causing flooding and other problems across New England. Irene's winds are down to 60 mph (95 kph).

A tropical storm warning is still in effect from Chincoteague, Va., up to Eastport, Maine.

Irene is forecast to weaken and become a post-tropical cyclone (one that was a tropical cyclone but that no longer has tropical characteristics) tonight.

This story was provided by OurAmazingPlanet, a sister site to LiveScience.

Don't let Hurricane Irene's waning strength fool you. The massive storm is still a major threat and could pound cities with severe weather for days, experts say.

The storm, at one point as large as one-third of the East Coast and as strong as a Category 3, has been a large storm for several days, and is creeping north at 13 mph (20 kph), now as a Category 1.

"Its slow movement up this coast makes this a problem as tropical-storm-force winds would have an impact for a full day at most places along the Mid-Atlantic coastline," a spokesperson with the National Hurricane Center told OurAmazingPlanet. [Hurricanes from Above: Nature's Biggest Storms]

The size of the storm matters with hurricanes because the bigger the storm, the longer it takes to move through an area. That slow march up the coast gives a storm like Irene more time to do serious damage with intense winds, torrential rains and storm surges.

Irene made landfall in Cape Lookout, N.C., today at about 7:30 a.m. EDT as a Category 1 storm, with maximum sustained winds of about 80 mph (129 kph). The storm has been lashing the Eastern Seaboard and at least two deaths were directly caused by the hurricane, according to news reports.

While Irene currently batters coastal North Carolina, rain from the storm's outer bands is currently falling in New York City well ahead of the predicted landfall near there. That weather won't go away anytime soon.

Forecasts show Irene hitting central Long Island, N.Y., sometime Sunday (Aug. 28), leaving New York City with the "clean side" of the hurricane — which is less powerful than the "dirty side" on a storm's right side as seen as above — and without the major storm surge.

Category 1 strength hurricanes have winds of at least 74 mph (119 kph). If the storm hits Long Island, tropical-storm-force winds, or worse, could pound New York City. Windows could shatter, buildings could sway and debris could rocket down the streets.

Hurricane-force winds are currently felt as far away as 90 miles (145 kilometers) from the eye. The strongest winds and the highest storm surge are on a hurricane's "dirty side," because winds in a hurricane rotate counterclockwise; so the strength of the storm on the "dirty side" is the hurricane's wind speed plus its forward velocity. The strength on the "clean side," or the left side, is the wind speed minus the velocity.

Because Irene was once a major hurricane, it has already developed a massive swell of water in the ocean that it will carry north and could spill onto low-lying areas. Storm surge, an abnormal rise in water, occurs when strong winds push water forward, ahead of a moving storm. Huge waves form on top of the surge, cresting and pounding the coast. This could be a problem for Long Island if those north-blowing winds, and the surge they push in front of them, hit it head-on.

In preparation for multiple days of severe weather and its aftermath, city-wide transit has been shut down across New York City. Residents in low-lying coastal areas are being told to evacuate. Thousands of flights have been canceled across the region.

• 6 Tips for Evacuating from Hurricane Irene
• Infographic: Storm Season! How, When & Where Hurricanes Form
• In Photos: Hurricane Irene

Email OurAmazingPlanet staff writer Brett Israel at bisrael@techmedianetwork.com. Follow him on Twitter @btisrael.

The extensive hurricane watches and warnings issued for Hurricane Irene were the most extensive in a decade, stretching from South Carolina to Maine. But Irene is not the first storm to spawn such extensive warnings. During Hurricane Floyd in 1999, "watches and warnings were issued for that hurricane from South Florida to Massachusetts," said Dennis Feltgen, public affairs officer for the National Hurricane Center.

Though Irene won't top that breadth of warnings, it may tie with Gloria.

"Hurricane Gloria in 1985 also had extensive warnings from the Carolinas to Maine," Feltgen told LiveScience. "Too close to call between Gloria and Irene — we'd have to do some serious research, which we can't do right now for obvious reasons — but Floyd is number 1."

Both Floyd and Gloria did wreak some havoc, with Gloria reaching Category 4 intensity on the Saffir-Simpson Hurricane Scale as it moved to the east of the Bahamas, before moving northward over the Outer Banks of North Carolina and making a second landfall on western Long Island. The storm resulted in eight deaths and $400 million in damage. [Are Category 6 Hurricanes Coming Soon?]

Floyd neared Category 5 status as it pounded the Bahamas in 1999, before threatening Florida and striking the coast of North Carolina. Ultimately, Floyd dumped as much as 2 feet (0.6 meters) of rain in some places along the east coast, resulting in 56 fatalities and $6 billion in property losses, according to the National Oceanic and Atmospheric Administration (NOAA).

A hurricane watch means sustained winds of 74 mph (119 kph) or higher (considered hurricane conditions) are possible in an area within the following 48 hours, according to NOAA. A hurricane warning means hurricane conditions are expected within that specified area, and these are issued 36 hours in advance of the anticipated onset of such winds.

Follow Live Science for the latest in science news and discoveries on Twitter @livescience and on Facebook.

Irene is predicted to be the latest in 2011's string of billion-dollar weather disasters. But for New York City, Irene is not shaping up to be the worst-case scenario it could be.

Forecasts show Irene hitting central Long Island, N.Y., sometime Sunday (Aug. 28), leaving New York City with the "clean side" of the hurricane and without the major storm surge. The city will mostly see "blustery rains and strong winds," said Eugene McCaul, an atmospheric scientist at NASA's Marshall Space Flight Center in Huntsville, Ala.

The U.S. National Oceanic and Atmospheric Administration (NOAA) has forecast around 8 inches (20 centimeters) of rain for New York City from Irene. [Infographic: Storm Targets: Where the Hurricanes Hit]

The strongest winds and the highest storm surge are on a hurricane's right side — the "dirty side" — as viewed from above. That's because winds in a hurricane rotate counterclockwise, so the strength of the storm on the "dirty side" is the hurricane's wind speed plus its forward velocity. The strength on the "clean side", or the left side, is the wind speed minus the velocity.

The worst-case scenario for New York City would be a major hurricane (Category 3 or higher on the Saffir-Simpson scale of hurricane strength) that remains out to sea and then whose eye plunges ashore just west of the Hudson Bay, bringing the full fury of wind, surge and punishing waves of the storm's dirty side into Manhattan and the surrounding metro area. If that were to happen, a storm surge of up to 30 feet (9 meters) would flood low-lying areas, according to the New York City Office of Emergency Management.

Irene, however, has weakened to a Category 1 storm with winds of 85 mph (140 kph) and has taken a different track, with its eye so far looking to hit slightly to the east of the city.

"We could still be unlucky here in the city and get a worse track, but it's just hard to happen," said Adam Sobel, an atmospheric scientist at the Lamont-Doherty Earth Observatory.

The city, especially the borough of Manhattan, sits in a crook, somewhat shielded by Long Island and areas to the south.

"The good thing is that it's kind of hard for a hurricane to get in at that angle," Sobel told OurAmazingPlanet.

A hurricane needs warm water for fuel. Since Irene has been hugging the coast, making landfall over the North Carolina coast, the storm has been robbed of fuel and is not as strong as it would have been were it out to sea. [Hurricanes from Above: Nature's Biggest Storms]

Irene is also not racing north at 50-plus mph (80 kph), as did a 1938 storm that devastated Long Island. Irene is lumbering along at 15 mph (24 kph), dumping tropical storm conditions on the East Coast.

This is not to say Irene won't be devastating. Nursing homes and hospitals in vulnerable coastal areas of the city have been evacuated. City-wide transit service will shut down Saturday at noon as a safety precaution, as will five area airports.

But when all is said and done, meteorologists will look back at the damage in New York City and likely say, "It could have been worse."

Email OurAmazingPlanet staff writer Brett Israel at bisrael@techmedianetwork.com. Follow him on Twitter @btisrael.

An instrument aboard a NASA satellite has allowed forecasters to take a peek beneath Hurricane Irene's roiling clouds to see how much rain the storm is making.

NASA's Tropical Rainfall Measuring Mission (TRMM) satellite radar produces three-dimensional images of storms' precipitation, and on Friday afternoon (Aug. 27) the radar showed that the southern half of Hurricane Irene's eyewall was gone.

Some strong precipitation did still exist in the remaining eyewall to the north of the eye.

The weakening of the inner-core precipitation structure as Irene approached North Carolina was similar to the pre-landfall weakening of the inner-core of Hurricane Isabel in 2003, the most recent hurricane to make landfall in North Carolina's Outer Banks.

TRMM showed that the highest towering thunderstorms were about 7.5 miles (12 kilometers) high.

Just before 8 a.m. EDT, on Saturday, August 27, Hurricane Irene made landfall near Cape Lookout, North Carolina.

The storm is a Category 1 hurricane packing maximum sustained winds of 85 mph (140 kmh) centered over eastern North Carolina, and moving north at 13 mph (20 kph), according to the most recent update from the National Hurricane Center. The storm is forecast to continue up the east coast.

Irene's hurricane-force winds extend 90 miles (145 km) from the center or 180 miles (290 km) in diameter. Tropical-storm force winds extend out 260 miles (418 km) from the center, making Irene about 520 miles (837 km) in diameter.

While Hurricane Irene is forecast to pass along the East Coast all the way to New England and then into Canada, the Friday afternoon overflight may be the last well-centered TRMM radar overflight because the orbit of the TRMM satellite stays within 35 degrees of latitude from the Equator.

• In Photos: Hurricane Irene's Fury
• 7 Surprises Hurricane Irene May Have in Store
• Infographic: Storm Season! How, When & Where Hurricanes Form

Satellites caught this image of Hurricane Irene making its way up the East Coast at 9:38 ET this morning (Aug. 27).

Irene has already made landfall near Cape Lookout, N.C., at 7:30 a.m. ET and is pummeling the coastal areas of that state. The storm is now a Category 1 hurricane on the Saffir-Simpson scale of hurricane strength with winds of 85 mph (140 kph). [Storm Targets: Where the Hurricanes Hi t]

Despite this weakening, Irene still poses a major threat because of its considerable size. Hurricane-force winds extend up to 90 miles (150 kilometers) from the center of the storm, and tropical storm-force winds extend 260 miles (415 km).

The first fringes of the storm's outer rain bands are beginning to be felt up to Jersey Shore and Long Island.

Hurricane conditions are expected to arrive in the mid-Atlantic states by this afternoon. Tropical storm conditions are expected to reach southern New England tonight.

Rains are expected to total between 6 to 10 inches (15 to 25 centimeters), with isolated areas seeing up to 15 inches (38 cm). These large amounts of rain increase the risk of flooding, especially in areas where the ground is already saturated from previous summer rainstorms.

Storm surge -- the mass of water the hurricane's ferocious winds push ahead of the storm -- is also a major concern along the coast.

Irene is the first hurricane and first major hurricane for what has been forecast to be an active season. The National Oceanic and Atmospheric Administration (NOAA) updated its forecast on Aug. 4, predicting 14 to 19 named storms (which include tropical storms and hurricanes), seven to 10 hurricanes and three to five major hurricanes. An average Atlantic hurricane season will see 11 named storms, six hurricanes and two major hurricanes. August through October are the peak months of the Atlantic hurricane season.

• 7 Surprises Hurricane Irene May Have in Store
• Infographic: Storm Season! How, When & Where Hurricanes Form
• In Photos: Hurricane Irene's Fury

When Hurricane Irene comes a-knocking, these buildings will start a-rocking.

Powerful winds have caused New York City's skyscrapers to sway back and forth for more than 100 years, leading to seasickness in their inhabitants and interest from engineers looking to mitigate the problem.

A little sway actually makes the building stronger, as structures with a bit of give can withstand higher stress than brittle forms. Despite how the rocking feels to the poor residents forced to endure a shaking floor, no modern skyscraper has been brought low by wind alone, said Christian Meyer, a professor of civil engineering at Columbia University. Modern innovations such as shock absorbers and balancers protect buildings from wind, while simultaneously lessening the drastic pitch and roll experienced at the top floor of the world's highest buildings.

"It's a fundamental structural engineering problem. On one side of the equation, you have the load effect. That can be a hurricane, an earthquake, a missile, anything. On the other side, you have the strength of the building, which you the engineer can control, and it must always be larger than or equal to the loading," Meyer told InnovationNewsDaily. "If you have a force that moves, that impact sets the structure into vibration. The main component is static pressure, but as soon as the pressure changes, motion begins. No matter how strong you make a building, they vibrate at some load."

As the building gets taller, the swaying gets worse, since wind speed and other loads increase with altitude. This can make the top floors of the world's biggest building unbearable. To prevent these top floors from shaking, engineers can deploy a number of different technologies.

One piece of equipment, called a tuned mass dampener, is essentially a 400-ton concrete pendulum that swings independently of the building. When the structure sways to one side, the dampening weight pulls the building back up straight. This technology is often used to make buildings earthquake, as well as hurricane, resistant.

Other buildings, such as the old World Trade Center Towers, featured individual shock absorbers for each floor. Each floor moved independently of the other ones, effectively turning the entire structure into a giant spring that can dissipate the energy that would cause the top levels to swing wildly, Meyer said.

Then there's Trump Tower in New York City's Columbus Circle, the building that used to make people sicker than a roller coaster.

"If a building vibrates too much, you get 'sick building syndrome.' That's a common problem," Meyer said. "There was this building at Columbus Circle, that’s now the Trump Tower, the building vibrated excessively during any major wind storm, and you saw hundreds of people coming out all green and yellow like they were seasick. Now Trump, smart guy that he is, realized he could get the building for very little money, but would have to do a major improvement. He put a shield wall in the center of the building, strong enough to stop the vibrations, but where no one could see it. He cured the building."

This story was provided by InnovationNewsDaily, sister site to LiveScience. Follow InnovationNewsDaily on Twitter @News_Innovation, or on Facebook.

Imagine this scenario: A hurricane has made landfall in a nearby town. You look outside but all you see outside is rain. No lightning. No thunder. No sign of the apocalypse. Then all of a sudden there's a big, fat tornado on the horizon.

People usually have days to prepare for a hurricane, but hurricane-spawned tornadoes (yes, hurricanes can and do spawn tornadoes) can catch people off guard. Hurricane Irene might not be a repeat of Hurricane Beulah, a 1967 storm that spawned more than 100 tornadoes across Texas, but the threat is real with any hurricane that makes landfall.

Tornadoes from Hurricane Irene are just one of the surprising things that people should look out for as the storm threatens landfall along the East Coast. [Infographic: Storm Targets: Where the Hurricanes Hit]

Tornado trouble

Hurricanes are basically a big, swirling mass of thunderstorms. Thunderstorms can spawn tornadoes, and hurricanes are no exception.But for a hurricane to spawn a tornado, the center of the storm needs to come a few hundred miles inland. When a hurricane makes landfall, friction causes winds at different heights in the storm to change directions, creating the wind shear needed to produce tornadoes.

Wide, wedge tornadoes are possible, but the twisters are usually weaker than their Great Plains counterparts, said Eugene McCaul, an atmospheric scientist at NASA's Marshall Space Flight Center in Huntsville, Ala.

"You don't tend to see these tall majestic tornadoes in land-falling hurricanes," McCaul told OurAmazingPlanet. "They tend to be these low, raggedy things."

Irene looks like it will brush the Carolinas, so a big hurricane-spawned tornado outbreak isn't likely there. If Irene makes landfall in Long Island, areas east of the storm could see some twisters, while New York City would likely see only heavy rains and winds. Irene could continue north, but hurricane-spawned tornadoes are rare in New England, McCaul said.

"I would not expect a huge tornado outbreak with this one," McCaul said.

Storm surge

Irene's strength has dropped to a Category 2 storm, and should not strengthen back to a major hurricane, according to the National Hurricane Center (NHC) (major hurricanes are Category 3 or higher on the Saffir-Simpson scale of hurricane strength). But Irene should still pack a punch, since it has already developed a massive swell of water that it will carry north.

Irene's swell could spill onto low lying areas. Storm surge, an abnormal rise in water, occurs when strong winds push water forward, ahead of a moving storm. Huge waves form on top of the surge, cresting and pounding the coast.

This could be a problem for Long Island, if those north-blowing winds, and the surge they push in front of them, hit it head-on.

A major hurricane (Category 3 or higher on the Saffir-Simpson scale of hurricane strength) could push more than 30 feet (9 meters) of storm surge into low-lying parts of New York City. That's a worst-case scenario; current computer models forecast a small chance of a storm surge of 2 feet (0.6 meters) in the region.

Whopper waves

Storm surge is like a rising tide that doesn't recede. Riding atop the storm surge are massive waves. The U.S. Navy has predicted wave heights of around 30 feet (9 m) for the New York region. The waves will repeatedly crash onto the coast.

Heavy rain

The U.S. National Oceanic and Atmospheric Administration (NOAA) has forecast around 8 inches (20 centimeters)  of rain for New York City. Other parts of the region could see up to 15 inches (38 cm).

Flooding

This past spring was sopping wet, so the ground is already saturated. The storm surge and heavy rain could bring widespread flooding across New York and New Jersey. In New York City, subway stations and sewer flooding could be a problem as the heavy rain overwhelms the underground tunnels.

Transit trouble

In an attempt to reduce the threat of subway flooding, New York Gov. Andrew Cuomo said that the entire New York City transit system will shut down tomorrow (Aug. 27) at noon.Elevated tracks would also be in danger from high winds.

An MTA spokesman told the New York Times that they cannot guarantee the safety of passengers on trains if winds are above 39 mph (63 kph) for a sustained period. Cuomo added that area bridges will also be closed if wind speeds exceed 60 mph.

Flooding could also be a problem at New York City's coastal airports. As a precaution, JetBlue has already cancelled 880 flights ahead of Irene.

Whipping winds

Category 1 strength hurricanes have winds of at least 74 mph (119 kph). Hurricane force winds are currently felt up to 90 miles (145 kilometers) from the eye. If the storm hits Long Island, tropical storm force winds, or worse, could pound New York City. Windows could shatter, buildings could sway and debris could rocket down the streets.

The New York City Office of Emergency Management advises high-rise dwellers to be prepared to move to the 10th floor or lower if necessary.

Email OurAmazingPlanet staff writer Brett Israel at bisrael@techmedianetwork.com. Follow him on Twitter @btisrael.

If Hurricane Irene's headed your way, you might be raiding the supermarket isles, hoping to stock up on food for the weekend. But don't think you need to fill the pantry with chips and salsa. There are plenty of ways to eat healthy, even if you're relying on prepackaged food.

"People go to the store and they're stocking up on junk food and party food," said Katherine Tallmadge, a registered dietitian and author of "Diet Simple" (LifeLine Press, 2011). "The truth is, it's really easy to eat nutritiously."

To meet your nutritional needs, you want to make sure your meals provide a combination of protein, fats and carbohydrates, said Heather Mangieri, a nutrition consultant and spokesperson for the American Dietetic Association.

"We want to make sure that we still have that combination…and that we're not just eating the same foods over and over again," Mangieri said. Mangieri recommends stocking up on the following foods:

• Vacuum-sealed packages of fish (tuna) or chicken: These are good sources of protein. You can also buy canned chicken and fish, but the vacuum packets don't require a can opener or draining, Mangieri said.
• Dried cereals: These foods are often fortified with vitamin and minerals, and can be eaten dry.
• Canned vegetables: These provide the nutrients of vegetables, but are higher in sodium than fresh vegetables. Rinsing with water (bottled water, if necessary) will reduce the sodium level somewhat.
• Shelf stable milk (such as powdered/canned milk): Milk is a good source of essential vitamins and minerals, including vitamin D, calcium and potassium.
• Fresh fruit and vegetables: While they don't have the shelf life of a Twinkie, fruits such as bananas and apples, and vegetables like tomatoes, can last for a few days. Try to buy fruit that is not completely ripe.
• Canned fruits: While not as good as fresh fruit, they are a good source of vitamin C.
• Nuts and seeds: these are a good source of protein, fiber and healthy fats.

Tallmadge recommends bean salad, which can be made from canned beans, and adding vegetables such as onions and celery.

"The options are just really limitless, I think," Tallmadge said. "Nobody is going to die of starvation being without a steak for a couple of days."

Pass it on: There are many ways to eat nutritiously during a disaster without a working stove or refrigerator.

This story was provided by MyHealthNewsDaily, a sister site to LiveScience. Follow MyHealthNewsDaily staff writer Rachael Rettner on Twitter @RachaelRettner. Like us on Facebook.

Hurricane Irene's looming threat on the weather forecast may compel you to stock up on bottled water and put up the shutters, but cities and businesses must also worry about dealing with flooded streets, emergency evacuations and power outages. Luckily, some have begun turning to an IBM supercomputer model that can help them decide on a practical response regarding anything from rainstorms to blizzards.

The "Deep Thunder" simulation not only delivers precise weather forecasts up to three days ahead of time for client cities or businesses, but also predicts possible storm damage on city or business infrastructure such as the power grid. Such information can help cities decide how many snow plows to put on the streets, or aid utility companies in sending out repair crews to fix downed power lines.

"We have to think about the business impact question," said Lloyd Treinish, chief scientist for IBM's Deep Thunder. "If all we can do is the weather, we haven't solved the problem yet even if there's value in the improved weather prediction."

Deep Thunder has already begun simulating the possible impact of Hurricane Irene for clients in New York City, as well as IBM's own labs located around New York State. It can provide anywhere from 24- to 84-hour forecasts depending on what the client needs and how much data is available.

"In general, the first 24 hours will be more accurate (e.g., for thunderstorms)," Treinish said. "But we have seen circumstances where we don't see a lot of difference in accuracy even three days ahead."

IBM previously did weather predictions for Florida during Hurricane Wilma in 2005. The National Weather Service forecasts had showed heavy rainfall and strong winds in Miami, but Deep Thunder more accurately predicted where rainfall would take place and showed how most of the hurricane threat would come from gusty winds.

Building better predictions

That's not to say IBM is trying to steal the thunder of the National Weather Service — the latter uses much of IBM's hardware and software technology. But whereas the National Weather Service must provide broad weather forecasts for the entire United States, IBM works with commercial clients to create more precise forecasts tailored to their needs.

"The National Weather Service has a very challenging mission of dealing with an entire country," Treinis told InnovationNewsDaily. "But what matters at the smaller scale of a utility company or city is very much dependent on local geographic constraints such as coastlines, rivers and topography."

Deep Thunder can draw data from weather stations operated by partner private networks — such as WeatherBug — or from weather sensors operated by a client city or business. It also uses public information from sources such as NASA and the National Oceanic and Atmospheric Administration that runs the National Weather Service.

Next, IBM's models consider the physics of how local geography and conditions affect even a monster storm such as Hurricane Irene. The urban geography and "urban heat island" effect of Manhattan can make for different weather conditions than what might take place near a much smaller city such as Providence, R.I.

The business impact

Modeling the physics of weather is just the first part of Deep Thunder's equation. The second part comes from simulating the exact layout of sewers, storage tunnels, buildings and power lines that could suffer storm damage from heavy rainfall, lightning strikes or flooding.

If all that's in place, Deep Thunder can figure out what seasonal and local weather conditions may lead to, say, the power going out. The culprit may be wind and fallen trees in one area, or the accumulation of snow and ice on power lines in another area. Historical weather data can also help predict the weather's impact on a business or city.

"You may have a common set of weather data in that you have both historical forecasts and historical measurements of wind, rain, temperature, humidity, but not all of it may be correlated to damage and impact," Treinis explained.

One North American utility company has worked with IBM to create a weather and outage prediction service to pinpoint such damaging effects of storms that can affect its 90,000 poles, wires and transformers. Deep Thunder can help position repair crews near the likeliest spots for storm damage, and even predict the number of workers who may be needed up to 72 hours before a storm.

Personalized weather forecasting

Deep Thunder won't directly help individuals plan whether they should cancel or go ahead with weekend driving, shopping or other plans ahead of Hurricane Irene — IBM is focused on bigger business clients. But the capability is there, and Deep Thunder is serving cities where people live and work.

"The individual's question about whether he or she should paint the house today or plan a barbecue is the same kind of problem a utility company might face, but it's obviously just a different scale of economic and societal impact," Treinis said.

Some IBM employees have actually used Deep Thunder's information to help decide whether to hold a barbecue or go sailing in the past, Treinis said. They may do that again as Deep Thunder tracks Hurricane Irene sweeping up the U.S. East Coast.

This story was provided by InnovationNewsDaily, a sister site to Live Science. You can follow InnovationNewsDaily senior writer Jeremy Hsu on Twitter @ScienceHsu. Follow InnovationNewsDaily on Twitter @News_Innovation, or on Facebook.

Astronauts on the International Space Station (ISS) got another eyeful of Hurricane Irene's increasing might today (Aug. 25) as their space capsule streaked over the monstrous Category 3 storm, which is barreling toward U.S. shores.

Ahead of the flyover, ISS video cameras revealed placid views of wispy white clouds scattered over the blue of the ocean. Then a huge mass of white appeared on the horizon: Hurricane Irene, a powerful debut storm for the 2011 Atlantic hurricane season.

Even from 220 miles (350 kilometers) above the Earth, the storm's power was on full view.

"This is a big storm," said astronaut Mike Fossum during a live video feed from the ISS this afternoon. As the ISS moved closer, a dense swirl of thick clouds filled the frame. [See the video of Irene here]

"This storm is doing a good job of filling up the Caribbean here," Fossum said, and pointed out what he called the "classic pinwheel structure" of the storm.

It took the ISS roughly six minutes to traverse the breadth of Hurricane Irene, which has organized itself into a colossal storm with a diameter one-third the length of the entire U.S. eastern seaboard.

"We're used to traveling a long way in a short amount of time," Fossum said, "and if this storm is stretching from Cuba to the Carolinas, this storm is one big, scary storm."

Fossum noted that even over North Carolina's outer banks, a region not projected to feel the effects of the storm until Saturday morning, "there's thin stuff that's actually spiraling way out here."

Hurricane Irene is packing winds of 115 mph (170 kph) with higher gusts, and could potentially strengthen in the coming day, according to the latest report from the National Hurricane Center.

The ISS crew has been watching Hurricane Irene's development for several days now.

Although the ISS circles the Earth every 90 minutes — 16 times a day — because it travels at a slight tilt in relation to the equator, the panorama on view below changes with each pass.

During a video interview earlier today with SPACE.com, a sister site to OurAmazingPlanet, Fossum noted that yesterday (Aug. 24) the storm appeared to undergo a pronounced change, and its structure became very uniform.

According to NASA's Mission Control, Hurricane Irene has a wind field 300 miles (480 km) wide, and shows no signs of weakening.

"Our prayers and our hopes are with the people who are hunkering down," Fossum said. "Good luck."

This story was provided by OurAmazingPlanet, sister site to LiveScience. Follow Andrea Mustain on Twitter @AndreaMustain.

The incoming fury of Hurricane Irene has prompted mandatory evacuations along the Outer Banks of North Carolina. These narrow strips of sand are barrier islands, shaped by thousands of years of waves and tides. Low-lying barrier islands are particularly vulnerable to pounding by storms. Left to their own devices, however, these sandy outposts are surprisingly resilient, geologists say.

"They have ways of protecting themselves," said George Voulgaris, a professor of marine and geological sciences at the University of South Carolina. "Yes, a hurricane will make lots of changes, but the barrier island will recover over time."

Humans can disrupt this process by building on barrier islands, disrupting the natural movement of sand, Voulgaris told LiveScience. [Photos: Beautiful & Ever-Changing Barrier Islands]

Building a barrier

No one is entirely sure how the barrier islands that line the East and Gulf coasts formed. One theory, says Brian Romans, a sedimentary geologist at Virginia Tech, is that the islands accumulate over time from sandbars. Waves break over a submerged sandbar, dropping sand and sediment with each crash, until an island gradually rises out of the ocean.

Another theory is that the islands form from spits of sand originally attached to the mainland. Waves carry sediment parallel to the shore to create these spits, and the connection between spit and shore is later broken by a storm.

"Either way, if the islands persist long enough and vegetation starts to grow on them, that stabilizes them even more," Romans told LiveScience.

According to Voulgaris, the sandbar theory is more likely along the East Coast, because there would have to be a headland protruding off the coast to provide a place for a spit to start growing. You don't see such headlands along the eastern coast, Voulgaris said.

10,000 years of change

The barrier islands along the East Coast are likely no older than 7,000 to 10,000 years, Voulgaris said. Earlier than that, he said, sea levels were rising rapidly as the last ice age ended and glaciers melted. Relatively stable sea levels in the last 7,000 to 10,000 years would have enabled the islands to form.

The islands' size and shape depend on the vagaries of the tides and waves. In South Carolina and Georgia, barrier islands tend to be wide and broken up by tidal inlets, in contrast to North Carolina's long and narrow Outer Banks. The reason, Voulgaris said, is that as you move south, the difference between high and low tide is greater. The larger volume of water moving past the southern islands toward the mainland opens more channels in the barrier islands, separating them. The tides also pile more sand on the back of barrier islands, widening them farther south. [Read: 7 Ways the Earth Changes in the Blink of an Eye]

Up north, the difference between high and low tide is smaller and the waves are stronger. The waves tend to move sand parallel to shore, smearing long, narrow strips of sand along the coast.

Regenerating islands

Storms can inundate barrier islands, so they aren't such a safe place to be when a hurricane is approaching. Some storms even wipe barrier islands off the map. This disappearing act isn't necessarily permanent, however.

"In the Gulf Coast, some of the barrier islands off the Mississippi River get washed out during big storms but then will come back the next season or a couple seasons later," Romans said. "Just the very tops of them get chopped off, essentially."

The islands are able to "grow" back because the sand doesn't move far, often just offshore, Voulgaris said.

"When the hurricane passes, milder waves come to rebuild, using the same sand that has been shifted to different locations," Voulgaris said.

The problem comes when humans build beach homes and fishing piers on these dynamic environments, Voulgaris said. Humans are unwilling to wait for nature to rebuild what's been lost, and man-made structures may disrupt the redistribution of sand, meaning that when milder waves do come, they have nothing to rebuild with. For instance, the Chandeleur Islands in the Gulf of Mexico have not recovered the  surface area they lost in Hurricane Katrina in 2005, LiveScience reported last year, because dams and other diversions along the Mississippi River are keeping island-building sediment out of the Gulf.

For the most part, though, it's not nature that suffers the most when a monster like Hurricane Irene is screaming toward shore.

"Hurricanes are very impressive. It's a lot of power. But the destruction is more in human-made structures," Voulgaris said. "Nature usually recovers."

You can follow LiveScience senior writer Stephanie Pappas on Twitter @sipappas. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.

Hurricane Irene

After the hitting Bahamas, Hurricane Irene is making its way toward the U.S. Northeast, forecasters predict. Here are the latest images of the hurricane. Above, Hurricane Irene on Aug. 24.

Irene Snapped from the International Space Station

A panoramic view of Hurricane Irene, photographed by the crew of the International Space Station on Aug. 22 from a point over the coastal waters of Venezuela. At the time, the newly-formed hurricane had 80 mph winds and was just north of the Mona Passage between Hispaniola and Puerto Rico, preparing to trek west-northwestward toward the southern Bahamas.

Steadily Strengthening

Above is another photo of the growing hurricane taken from the International Space Station on Aug. 23. This view looks toward the southwest at part of Hurricane Irene as it brews near the northern Bahamas, including Great Abaco Island on the photo's lower right and Andros Island under a thunderstorm on the center right. Irene was probably centered over Acklins Island when the photo was snapped, according to meteorologists.

Bahamas Bull's-Eye

Hurricane Irene hit the southeast Bahamas on Wednesday (Aug. 24), passing directly over Crooked Island. In the above satellite image, the hurricane's eye is somewhat obscured by the island.

The Rainbow Before the Storm

This breathtaking shot, taken the morning of Aug. 24 in Boynton Beach, Fla., shows a rainstorm's looming clouds over a rainbow, with a faint double rainbow overhead. While Hurricane Irene was hitting the Bahamas at the time, the storm was gathering strength, with gusty winds and rain affecting Florida's beaches.

Heavy Rainfall

This 3-D view of Hurricane Irene was captured on August 24 by a NASA satellite. The red areas indicate rainfall of about 2 inches or more per hour, while the yellow and green areas show moderate rainfall of between .78 to 1.57 inches per hour.

Looming Storm Clouds

Dania Beach, a city in Broward County, Fla., also saw fearsome thunderstorm clouds approaching on the morning of Aug. 25.

Whipping Winds

This satellite image shows Hurricane Irene directly over the southern Bahamas on Aug. 24. The category 3 hurricane's winds increased to speeds of 120 mph (195 kmh) as it passed over the area.

Projected Path

This National Weather Service graphic, based on National Hurricane Center data, predicts Hurricane Irene's path from Aug. 25 to Aug. 30 along the U.S. East Coast. With surface wind speeds equal or exceeding 58 mph (93 kph), state and National Weather Service officials have begun urging New Jersey and North Carolina residents to prepare for Hurricane Irene now. Even New York City Mayor Michael Bloomberg is taking the hurricane's threat seriously, advising New Yorkers to stay alert, as the storm could come near New York City on Aug. 28.

Likely Landfall?

Another graphic depicting the hurricane's projected path. If Irene makes landfall in the U.S., it will become the first hurricane to do so since destructive and costly Hurricane Ike pummeled the Texas coast in 2008.

Harvest Rush

In preparation for Irene's arrival, workers on Faith Baptist Church Road in Edgecombe County, N.C., are harvesting ripe tobacco as quickly as possible in a preventative effort to limit the amount of damage the storm's whipping winds may unleash upon this summer's crop.

Monster Irene and Smaller Tropical Depression

This satellite image captured Hurricane Irene moving through the Bahamas on the morning of Aug. 25. To the east was the newly formed Tropical Depression 10, which is on the far right of the image. Irene is much larger than the tropical depression 10, as the hurricane is estimated to be about 1/3 the size of the entire U.S. East coast.

No Eye?

At the time this NASA satellite image was taken on Aug. 25 at 8:15 a.m. ET (1215 UTC), Hurricane Irene was still packing a punch with 115 mph winds. Although the eye has disappeared from this NOAA GOES-East satellite imagery, the storm is not weakening and appears to be going through an eyewall replacement cycle. The National Hurricane Center is still predicting Irene to reach category 4 status within the next day. Hurricane and tropical storm watches are in effect for much of the Carolina coastline.

Irene from Space

This photo of Hurricane Irene was photographed from onboard the International Space station at 19:14:09 GMT (3:14 p.m. ET) on Aug. 24, 2011. The image, captured with a 38-mm lens, reveals the eye at center frame.

Ominous Clouds

Vilano Beach, Fla., also got a taste of Hurricane Irene's still far-off fury on the morning of Aug. 26.

Irene Close-Up

Another photo taken from onboard the space station on Aug. 24 reveals the eye of Hurricane Irene.

Storm Progression

The above NOAA image shows the position of Hurricane Irene and Tropical Storm 10 on the morning of Aug. 26, with Irene about 375 miles south-southwest of Cape Hatteras, N.C., according to the National Hurricane Center.

Threatening Thunderhead

Above is another shot of Dania Beach in Broward County, Fla., as threatening storm clouds raced overhead before the rain began to fall during the early morning hours of Aug. 25.

Getting Closer

This image was taken by NOAA's GOES-EAST satellite on Aug. 26 as Hurricane Irene moved between the Bahamas toward the U.S. East Coast.

Aquamarine Sky

This amazing photo of approaching storm clouds was taken on Aug. 25, while workers and officials in Washington, D.C., scrambled to prepare for Hurricane Irene to make landfall on Saturday in North Carolina. The area has received a tropical storm warning, leading to train service cancelations and Mayor Vincent Gray urging residents to study emergency evacuation routes from Washington.

Flying By

This photo captured the west edge of Hurrican Irene as it passed by northern Florida. It was taken the morning of Aug. 26, about 20 miles west of Jacksonville, Fla.

Looking Up

Cameras onboard the International Space Station captured this view from 230 miles above the Earth of Hurricane Irene as it churned over the Bahamas at 3:10 p.m. EDT on Aug. 24, 2011. (This is a still from a video.)

Sunrise Before the Storm

This shot was taken on the New Hampshire Seacoast in Rye. Though Hurricane Irene has yet to reach there, it painted a beautiful sky on the morning of Aug. 27, 2011. [Image Gallery: Sunrise and Sunsets]

Virginia Prepares

irginia National Guard Soldiers from the West Point-based 237th Engineer Company prepare for possible duty in response to Hurricane Irene in Onancock August 26 by staging vehicles, equipment and fuel. The Virginia National Guard has been authorized to bring up to 300 personnel on state active duty for possible missions including high water transport and light debris removal.

Amelia Meets Irene

Photo taken on Aug. 26, 2011, as Hurricane Irene passes Amelia Island, one of the southernmost Sea Islands, a chain of barrier islands along the U.S. east coast. [See more photos of barrier islands]

Vulnerable Island

Amelia Island under the fury of Hurricane Irene on Aug. 26, 2011. Like other barrier islands, Amelia has been shaped by years and years of waves and tides. Though these narrow stretches of sand are vulnerable to pounding by storms, geologists say they are surprisingly resilient. [Read: How Barrier Islands Survive Storms]

Rough Surf on Amelia

Hurricane Irene makes herself known, with dark storm clouds and rough surf on Amelia Island, Fla.

Amelia Island

Hurricane Irene pass over Amelia Island, Fla., on Aug. 26, 2011.

Irene's Surf

A surfer and birds at sunrise at Kill Devil Hills, N.C. on Aug. 26, 2011, under the dark skies cast by Hurricane Irene.

Outer Banks & Irene

Sunrise at Kill Devil Hills, on the Outer Banks, N.C., on Aug. 26, 2011.

TV Crew Watches Irene

A TV crew sets up on the beach in Kill Devil Hills, on the Outer Banks, N.C., on Aug. 26, 2011.

Astronauts on the International Space Station (ISS) got an eyeful of Hurricane Irene's increasing might today (Aug. 25) as their space capsule streaked over the monstrous Category 3 storm, which is barreling toward U.S. shores.

Ahead of the flyover, ISS video cameras revealed placid views of wispy white clouds scattered over the blue of the ocean. Then a huge mass of white appeared on the horizon: Hurricane Irene, a powerful debut storm for the 2011 Atlantic hurricane season.

Even from 220 miles (350 kilometers) above the Earth, the storm's muscle was on full display.

"This is a big storm," said astronaut Mike Fossum during a live video feed from the ISS this afternoon. As the ISS moved closer, a dense swirl of thick clouds filled the frame. [See the video of Irene here.]

"This storm is doing a good job of filling up the Caribbean here," Fossum said, and pointed out what he called the "classic pinwheel structure" of the storm.

It took the ISS roughly six minutes to traverse the breadth of Hurricane Irene, which has organized itself into a colossal storm with a diameter one-third the length of the entire U.S. eastern seaboard.

"We're used to traveling a long way in a short amount of time," Fossum said, "and if this storm is stretching from Cuba to the Carolinas, this storm is one big, scary storm."

Fossum noted that even over North Carolina's outer banks, a region not projected to feel the effects of the storm until Saturday morning, "there's thin stuff that's actually spiraling way out here."

Hurricane Irene is packing winds of 115 mph (170 kph) with higher gusts, and could potentially strengthen in the coming day, according to the latest report from the National Hurricane Center.

The ISS crew has been watching Hurricane Irene's development for several days now.

Although the ISS circles the Earth every 90 minutes — 16 times a day — because it travels at a slight tilt in relation to the equator, the panorama on view below changes with each pass.

During a video interview earlier today with SPACE.com, a sister site to OurAmazingPlanet, Fossum noted that yesterday (Aug. 24) the storm appeared to undergo a pronounced change, and its structure became very uniform.

According to the NASA ground crew, Hurricane Irene has a wind field 300 miles (480 km) wide, and shows no signs of weakening.

"Our prayers and our hopes are with the people who are hunkering down," Fossum said. "Good luck."

• Video: See Irene from the International Space Station
• Infographic: Storm Season! How, When & Where Hurricanes Form
• In Photos: Hurricane Irene

Andrea Mustain is a staff writer for OurAmazingPlanet, a sister site to LiveScience. Reach her at amustain@techmedianetwork.com. Follow her on Twitter @AndreaMustain.

This weekend, Hurricane Irene could bring massive storm surge, fierce winds, torrential rains and flash floods to New York City and other portions of the Mid-Atlantic and Northeast. The scary weather could grind transportation to a halt and force coastal evacuations. 

New York's dense, developed coastline makes the city among the most vulnerable to hurricane-related damage, according to the New York City Office of Emergency Management (OEM).

"Due to regional geography, hurricanes in New York City — though infrequent — can do more damage than hurricanes of similar strength in the southern United States," the OEM said in a statement.

Dirty side, clean side

The storm is expected to hit the New York City region by Sunday, though exactly what path it may take remains uncertain. The latest forecasts from the National Hurricane Center put the most likely path as hitting slightly to the west of the city, though it's possible the storm's course could change before then.

Forecasters say it's too early to tell if Irene will be a repeat of the infamous Long Island Express hurricane of 1938, the benchmark by which all New York City hurricane fears are compared. Forecasters will have a better idea once Irene passes North Carolina.

As the storm moves north, the Atlantic's cold water could weaken the storm because cold water is poor fuel for hurricanes.

Irene could still be a Category 1 storm when it reaches the New York region, however. The storm's "dirty side," the right side where the winds are strongest, and blow toward the north, could pack a punch on Long Island.

"It's actually kind of the worst-case scenario for the people of Long Island," said Jeff Weber, an atmospheric scientist at the University Corporation for Atmospheric Research (UCAR) in Boulder, Colo.

If the current forecast holds, New York City should be on the storm's left, or "clean side," which is where the winds are weaker. The likelihood of window-shattering winds is not very high right now, said Adam Sobel, an atmospheric scientist at the Lamont-Doherty Earth Observatory.

Too much rain

A Category 1 storm hitting Long Island would mean tropical storm conditions, or worse, for New York City. [Which US Cities Are Most Vulnerable to Hurricanes?]

"There could be an awful lot of rain, and possibly storm surge," Sobel said.

The U.S. National Oceanic and Atmospheric Administration (NOAA) has forecast 12 inches (30 centimeters) of rain for New York City over the next five days.

"I think we're going to have a serious flooding concern," Weber said, because the wet spring saturated the soil across the region, meaning they won't be able to absorb the influx from Irene. That water would instead build up on the ground, creating prime conditions for flash floods.

As if water from above wasn't bad enough, water could spill forth from the sea. Storm surge, an abnormal rise in water, occurs when strong winds push water forward, ahead of a moving storm. Huge waves form on top of the surge, cresting and pounding the coast.  Storm surge

This could be a problem for Long Island, if those north-blowing winds, and the surge they push in front of them, hit it head-on.

A major hurricane (Category 3 or higher on the Saffir-Simpson scale of hurricane strength) could push more than 30 feet (9 meters) of storm surge into low-lying parts of the city. That's a worst-case scenario; current computer models forecast a small chance of astorm surge of 2 feet (0.6 meters) in the region.

The U.S. Navy has predicted wave heights of around 30 feet (9 m) for the New York region.

"It's sort of a big storm and sort of moving slowly so the wind will be pushing on the water for a longer amount of time," Sobel told OurAmazingPlanet.

Irene's early strengthening could make the surge particularly bad, even after the hurricane weakens. Because Irene has already strengthened to a Category 3, its strong winds have developed a swell of water that it could carry northward.The swell may wane, but it will be higher than if Irene had stayed as a Category 1 throughout its course.

"When they ramp up to a 3 or 4, they kind of keep those swells with them as they move up the coast," Weber said.

This was the case with Hurricane Katrina, which got up to Category 5 strength before hitting the Gulf Coast as a Category 3. Its previous ferocious strength (along with its enormous size) meant it brought a whopping surge with it. Storm surge was about 24 to 28 feet (7 to 8.5 meters) along the Mississippi coast across a swath about 20 miles (32 kilometers) wide, and penetrated several miles inland, tearing up Interstate 10, according to the NHC.

The OEM has set up evacuation zones throughout the city to shelter people who live within 10 blocks of the coast. (Click here to find out if you live in a hurricane evacuation zone.)

People who live in high-rise buildings should be ready to move to the 10th floor or below if winds become strong enough, the OEM says.

Email OurAmazingPlanet staff writer Brett Israel at bisrael@techmedianetwork.com. Follow him on Twitter @btisrael.

Tourists and residents are fleeing the coastal islands of North Carolina as Hurricane Irene approaches the East Coast of the United States today (Aug. 25). But if history is any guide, some people in the path of the hurricane will refuse to leave their homes and businesses. Why would anyone put themselves on a collision course with a Category 3 storm?

Everyone has their own pros and cons to weigh when making their evacuate-or-not-to-evacuate decisions, said Josh Klapow, a psychologist at the University of Alabama, Birmingham, who specializes in disaster preparedness. One major factor, Klapow told Livescience, is how tough evacuation is likely to be.

"They don't go because, frankly, they don't believe that the impact of the event is going to be dangerous enough to warrant leaving the house," Klapow said.

Irene evacuations

In Dare County, N.C., which contains a long line of vulnerable barrier islands, about 150,000 visitors were ordered to evacuate today. A mandatory evacuation for all residents goes into effect at 8 a.m. local time tomorrow (Aug. 26). In New York, Mayor Michael Bloomberg told reporters that officials were preparing to order evacuations from low-lying areas of the city if conditions become dangerous.

Evacuating large urban areas can be difficult. In 2005, traffic out of Houston came to a standstill and drivers ran out of gas after officials urged residents to flee the path of Hurricane Rita. About 100 people are estimated to have died in the Rita evacuation in Texas from traffic accidents, heatstroke and other causes.

Bad evacuation experiences can make some people believe that weathering a storm is preferable to the trauma of heading out of town, Klapow said. In 2008, during Hurricane Ike's fury, as many as 140,000 residents ignored evacuation warnings in Texas, choosing to shelter in place. One contributing factor may have been the botched Rita evacuation. (Ike caused deaths and extensive damage across parts of the Caribbean and the coasts of Texas and Louisiana.)

"If your house didn't get destroyed, all of the information that's feeding into your experience is, 'Evacuation is horrific, my house didn't get destroyed, so why would I go?'" Klapow said.

Some people stay because they're very attached to their homes and possessions, Klapow said. Others who've survived earlier storms may conclude that they can handle anything that comes their way. That's not necessarily true, Klapow said.

"If you rode out three storms, then all you know is that you rode out three storms," he said.

How to prepare

Financial concerns, such as being unable to afford a motel or transportation, can keep some people from evacuating. If resources are an issue, residents should call their local emergency management services to find out where to go and how to get there, Klapow said. The Humane Society recommends making evacuation plans for pets, as well.

Anyone in an area where evacuation could become necessary should plan where they're going and how they'll get there, Klapow said. He also urged residents in potential storm-impact areas to gather together medications, basic first aid supplies, food and water.

"If you've got some water, a little bit of food, a basic first aid kit and your meds, then if you need to get out for a couple days, you're going to be okay," he said.

You can follow LiveScience senior writer Stephanie Pappas on Twitter @sipappas. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.

As the East Coast braces for potential high surf, rains and winds from Hurricane Irene, the Humane Society of the United States recommends that people build their pets into their evacuation plans.

"It is crucial that residents are prepared to take pets with them if asked to evacuate in the face of this potentially destructive storm," Laura Bevan, the Humane Society's Eastern regional director, said in a statement. "If it isn't safe for you, it isn't safe for your pets."

Irene, now a category 3 storm with winds of up to 115 miles per hour (185 kilometers per hour), is forecasted to travel up the East Coast of the U.S. through the weekend, potentially threatening coastal areas from the Carolinas to New England.

Even if there is no immediate evacuation order in your area, residents in potential hurricane impact zones are advised to take a few basic preparedness steps, including knowing where to go in the event of an evacuation, stocking up on food and water, and making sure important documents and medications are easy to access.

For people with pets, evacuation can be slightly more complicated. Many evacuation shelters don't accept pets, the Humane Society reported, so pet owners should check with their local animal shelter or emergency management service to find out if there will be pet-friendly shelters in the area. Hotels and motels sometimes lift "no pet" restrictions in emergencies, but residents should ask ahead.

In addition to an emergency plan, pet owners should have an emergency supply kit for their pets. According to the Humane Society, this kit should include:

-       At least three days of pet food and water in airtight, waterproof containers

-       Bowls for food and water

-       Current photos and physical descriptions of pets, in case they should become lost

-       Medications, vaccination records and any pet first-aid supplies

-       Comfort items such as a toy or blanket

-       Small garbage bags for waste

-       A leash, harness and sturdy carrier large enough to be used as a sleeping area for dogs

-       For cats, a litter box, litter and a sturdy carrier.

For more tips and advice on other pets, visit humanesociety.org/prepare.

You can follow LiveScience senior writer Stephanie Pappas on Twitter @sipappas. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.

Hurricane Irene, the first hurricane of the 2011 Atlantic season, has now organized itself into a major storm and is barreling northward toward the United States' eastern coastline.

Although the storm is now centered over the Bahamas, hurricane watches are in effect along the North Carolina coast.

The hurricane is on track to affect large swaths of the Eastern Seaboard, and as far north as New York City public officials are warning of possible evacuations. [Related: Which US Cities Are Most Vulnerable to Hurricanes?]

Warm water, weak wind shear

Several factors have contributed to the growing strength of the storm, now a Category 3 hurricane packing winds of 115 mph (185 kph), which could intensify in the coming days.

"First and foremost, it has to be over warm waters," said Scott Braun, a research meteorologist at NASA's Goddard Space Flight Center in Greenbelt, Md. "The key source of energy for the hurricane is the water vapor that's evaporated from the ocean surface."

Waters need to be around 79 degrees Fahrenheit (26 degrees Celsius) to fuel a hurricane, and Braun said ocean surface temperatures in the area where Irene formed and is now growing are around 84 F (29 C), "so it has sufficient energy."

In addition, hurricanes like peace and quiet to get organized, Braun said. The storms require low wind shear — meaning a low contrast between wind speeds at the surface of the ocean and higher up in the atmosphere. "And in this particular case the shear appears to have been quite weak," Braun said.

Weak wind shear appears to have played a major role when Hurricane Irene jumped from a Category 1 to a Category 3 storm yesterday (Aug. 24). [Hurricane Irene's Surge in Strength Caught on Video]

Hurricane Irene did weaken momentarily around Tuesday (Aug. 23), from a Category 2 to a Category 1 storm, but Braun said the change didn't represent a big shift in the storm's intensity.

"You can't read too much into that," Braun said. "Looking at the data, it went from 85-knot winds to 80-knot winds, so it was right at the threshold between the two categories." (85 knots is about 98 mph, or 157 kph.)

East Coast impacts

Irene has also been helped by the fact that it has been traveling over ocean water and small Caribbean islands, which are unlikely to hamper its strength.

When hurricanes move over land, they are deprived of their main energy source — warm ocean water. In addition, "you also have increased friction over land," Braun said, and topographical features such as mountains can disrupt the storm's circulation.

However, until the storm hits land — and it's not clear when and where this will happen —  conditions that stoke intensification are readily available.

Warm water temperatures of roughly 84 degrees (29 C) extend as far north as North Carolina's outer banks, Braun said, providing the storm with ample fuel as it tracks up the East Coast.

Hurricane-hunting aircraft have been flying into the storm since Saturday (Aug. 20).  The latest update from the planes indicates the storm has recently turned north-northwest as expected, and forecasters have shifted the projected track of the storm slightly westward, closer to the U.S. coastline.

"Significant impacts are likely along the United States East Coast regardless of the exact track it takes," according to the latest report from the National Hurricane Center.

"It's still moving over ocean temperatures that can more than support a Category 4 storm," Braun said, "and as long as the wind shear stays favorable, there's not really much to stop it from getting up to a 4."

Category 4 storms are those with wind speeds between 131 and 155 mph (210 and 249 kph).

Editor's Note: This story has been altered to reflect the following changes: Ocean waters begin to cool closer to North Carolina than Delaware/Maryland. In addition, hurricanes require water temperatures of just 79 degrees Fahrenheit (26 degrees C) for fuel, not 82 degrees.

Andrea Mustain is a staff writer for OurAmazingPlanet, a sister site to Live Science. Reach her at amustain@techmedianetwork.com. Follow her on Twitter @AndreaMustain.

Emergency officials in each state designate evacuation zones, and formulate plans for how residents in each zone should evacuate if it becomes necessary for them to do so. If you live near the East Coast, your home may be located in an evacuation zone. If it is, and especially if you live in a high-rise building or mobile home, you may be ordered to evacuate in the coming days if Hurricane Irene continues to gain steam along its current path. What should you do now to prepare?

1) Make a plan.

Find out whether you live in an evacuation zone at your state's emergency preparedness website. Here are the links for New York, South Carolina, North Carolina, Virginia, New Jersey, Maryland, Massachusetts.

The National Hurricane Center recommends evacuating to the nearest safe spot (even if that's within the same county, as long as it's outside the evacuation zone) so as to minimize travel time and traffic jams. If you plan to go to a hotel or motel, make reservations ahead of time. Wherever you plan to go, call your loved ones before you leave to let them know where you'll be, because strong winds, storm surges and floods from Hurricane Irene could disrupt cellphone service.

2) Gas up car.

NBC News' Kerry Sanders has covered every major hurricane in the past 30 years. Before Hurricane Irene arrives, he wrote in a recent story, "The number one item folks should get now is: a full tank of gasoline. It's not so much that the stations will run out of gas, but rather it's a good proactive move to avoid wasting time waiting in long lines later."

If you don't have a car, make plans with friends or neighbors who do. If no one you know has a car, see the next tip.

3) Pack car with food/water/precious items.

Keep Hurricane Katrina in mind. You can never be sure how events will progress in the days after a hurricane hits. It's best to be prepared for anything, and that means stocking up on water (1 gallon per person per day) and some nonperishable food, such as granola bars, canned food, peanut butter, jelly and a loaf of bread. Store these in a cooler in your car.

Must-have items — which you must take, whether you have a car or just a backpack — are medicine, essential child care items such as diapers, and insurance information.

If you have a car, you'll also want to take valuables with you. Take laptops, photo albums, passports and anything else you consider irreplaceable. If you don't have a car, travel more lightly. Your state may have a plan for transporting transit-dependent people to the nearest emergency shelter (where there will be water and restrooms). Find out from your state's emergency management website.

4) Take photos of the inside of your home.

Take photographs or video of each room in your home, and in particular, precious items. If your house is torn apart by wind, or swept away by the storm surge, this documentation will come in handy later on when you're filing a claim with your insurance company. Photographs are particularly useful for small items that you might otherwise forget in the big picture of trying to reassemble your life. [A History of Destruction: 8 Great Hurricanes]

5) Prepare your home.

Secure any loose items so that strong winds or floods don't carry them away. Move small knick-knacks from shelves into drawers, for example. Nail plywood over your windows. Don't just open them or tape them shut — neither will protect the inside of your house from water or broken glass. If you're directed by your state's emergency managers to stick it out in your house rather than evacuate (if they're only evacuating people in mobile homes and you live in a house with a foundation, for example), stay away from your windows — especially if you haven't boarded them up.

6) Be vigilant.

The National Hurricane Center constantly updates their website with the latest information about Hurricane Irene. Keep track of the storm's path. Officials at each state's office of emergency management decide whether to give the go-ahead for people to evacuate, and in which areas. Stay on top of what they're saying via their website, TV or the radio. If they order you to evacuate, do so immediately.

This article was provided by Life's Little Mysteries, a sister site to LiveScience. Follow us on Twitter @llmysteries, then join us on Facebook. Follow Natalie Wolchover on Twitter @nattyover.

The eye of Hurricane Irene, now a major storm with 115 mph (185 kph) winds, was spotted by infrared satellite sensors as the storm swirled over the Bahamas earlier today (Aug. 24).

After a brief dip in its power yesterday, Irene re-strengthened overnight and has now reached Category 3 status, making it the first major hurricane of the 2011 Atlantic season. Category 3 hurricanes on the Saffir-Simpson scale of hurricane strength have winds between 111 to 130 mph (178 to 209 kph).

The last hurricane hunter reconnaissance mission also measured a central pressure of 966 millibars a decrease from the previous flight, and further indication of the storms organization and intensification.

Irene's predicted path will take it up through the Bahamas, then up to the Outer Banks of North Carolina and along the coast of the Mid-Atlantic and Northeast states where it could finally make landfall. The storm would like weaken some in the cooler waters off the northern states, though it could still bring torrential rains and strong storm surge. [Related: Could New York City Handle a Hurricane?]

Rainfall in the Bahamas is expected to total between 6 to 12 inches (15 to 30.5 centimeters), with some isolated pockets of 15 inches (38 cm). Storm surge in the islands is expected to be as much as 7 to 11 feet (2 to 3.4 meters) above normal tide levels.

Irene is the first hurricane and first major hurricane for what has been forecast to be an active season . The National Oceanic and Atmospheric Administration (NOAA) updated its forecast on Aug. 4, predicting 14 to 19 named storms (which include tropical storms and hurricanes), seven to 10 hurricanes and three to five major hurricanes. An average Atlantic hurricane season will see 11 named storms, six hurricanes and two major hurricanes. August through October are the peak months of the Atlantic hurricane season.

• History of Destruction: 8 Great Hurricanes
• Video: Hurricane Irene Seen from Space Station
• Hurricanes from Above: See Nature's Biggest Storms

After a brief dip in its power, Hurricane Irene has re-strengthened and has now reached Category 3 status, making it the first major hurricane of the 2011 Atlantic season.

Irene is now barreling through the Bahamas with winds of 115 mph (185 kph) and could strengthen further. Category 3 hurricanes on the Saffir-Simpson scale of hurricane strength have winds between 111 to 130 mph (178 to 209 kph).

Irene's predicted path will take it up through the Bahamas, then up to the Outer Banks of North Carolina and along the coast of the Mid-Atlantic and Northeast states where it could finally make landfall. The storm would like weaken some in the cooler waters off the northern states, though it could still bring torrential rains and strong storm surge. [Related: Could New York City Handle a Hurricane?]

Rainfall in the Bahamas is expected to total between 6 to 12 inches (15 to 30.5 centimeters), with some isolated pockets of 15 inches (38 cm). Storm surge in the islands is expected to be as much as 7 to 11 feet (2 to 3.4 meters) above normal tide levels.

Irene is the first hurricane and first major hurricane for what has been forecast to be an active season. The National Oceanic and Atmospheric Administration (NOAA) updated its forecast on Aug. 4, predicting 14 to 19 named storms (which include tropical storms and hurricanes), seven to 10 hurricanes and three to five major hurricanes. An average Atlantic hurricane season will see 11 named storms, six hurricanes and two major hurricanes. August through October are the peak months of the Atlantic hurricane season.

• History of Destruction: 8 Great Hurricanes
• Video: Hurricane Irene Seen from Space Station
• In the Eye of the Storm: NASA's Hurricane Hunters

Hurricane watchers circle Aug. 20 on their calendars every year. This is the "magic" date when hurricane season seems to kick into high gear.

Like clockwork, Hurricane Irene — the Atlantic's first hurricane of 2011 — was born on Aug. 22, later strengthening to a Category 2 hurricane. Last year was another good example of an active storm season ramping up after Aug. 20. All of the 2010's major hurricanes (those of Category 3 or higher) formed after Aug. 20, starting with Danielle on Aug. 21.

Aug. 20 seems to be special because around this time, the air and ocean are in just the right state to foster and feed the monster storms. In climate-speak, this time of year is when vertical shear (a change in wind directions with height) in the atmosphere is low enough and sea surface temperatures are warm enough to create big storms.

"Now, storms can get going before Aug. 20, but this is typically about when they start," said Phil Klotzbach, a hurricane forecaster at Colorado State University in Fort Collins.

This year was typical in saving its biggest storm so far for after Aug. 20, but it was unprecedented in the number of tropical storms that fizzled before reaching hurricane strength. The 2011 hurricane season began with eight tropical storms that all failed to become hurricanes before Irene broke the streak. One reason for the flurry of tropical storms is that scientists are naming more tropical storms than in past years, Klotzbach said.

The last time a hurricane season saw so many tropical storms before seeing a hurricane was 2002. That year, Tropical Storm Gustav eventually broke the string by strengthening to a Category 4 hurricane. Gustav struck Louisiana on Sept. 8, killing 112 people.

The hurricane forecast from the U.S. National Oceanic and Atmospheric Administration (NOAA) calls for 14 to 19 named storms (which include tropical storms and hurricanes), seven to 10 hurricanes and three to five major hurricanes (Category 3 or higher).

Irene is currently a Category 2 storm, with winds of up to 100 mph (160 kph), and is the first serious threat to the U.S. coast in three years. If no hurricanes make landfall in 2011, this three-season lull will be the longest in recorded history.

• History of Destruction: 8 Great Hurricanes
• In the Eye of the Storm: NASA's Hurricane Hunters
• Natural Disasters: Top 10 U.S. Threats

Email OurAmazingPlanet staff writer Brett Israel at bisrael@techmedianetwork.com. Follow him on Twitter @btisrael.

As Hurricane Irene nears the United States, an American astronaut has snapped a stunning view of the powerful storm from space.

NASA astronaut Ron Garan photographed the Category 2 hurricane Monday (Aug. 22) while gazing down on Earth from the International Space Station, which he and five other spaceflyers currently call home.

"Hurricane #Irene #FromSpace as it passed though the Caribbean yesterday (8/22/11) @ 7:34pm GMT," Garan wrote in a Twitter post that accompanied the photo. "Plz Be Prepared." Garan posts updates about life on the space station 220 miles (354 kilometers) under the name @Astro_Ron. [See Ron Garan's photos of Hurricane Irene and Earth]

Hurricane Irene is the first hurricane to form during the 2011 Atlantic hurricane season, which began on June 1. It is currently a Category 2 type storm on the Saffir-Simpson scale of hurricane strength, with wind speeds of about 100 mph (160 kph).

Irene is poised to become a major hurricane today (Aug. 23) or tomorrow.

Several weather satellites in orbit have been tracking Hurricane Irene, beaming down amazing images of the powerful storm. Video cameras on the International Space Station have also caught views of the hurricane. [Video: Hurricane Irene Seen From Space Station]

There have been nine named storms this hurricane season (including Irene), but all the previous tempests remained tropical storms (defined as having winds between 39 and 73 mph, or 63 and 118 kph).

"The National Hurricane Center noted on Aug. 22 that Irene is expected to produce total rainfall accumulations of 5 to 10 inches across Puerto Rico, The Virgin Islands, the Dominican Republic, Haiti, the Southeastern Bahamas and The Turks and Caicos Islands," NASA officials wrote in a statement. "Isolated maximum amounts of rainfall may reach up to 20 inches."

Irene marks a record in the most named storms in the season before the appearance of a hurricane — in all other seasons on record, names did not go past "G" without the formation of a hurricane. Irene is also poised to be the first hurricane to make landfall in the United States since Ike in 2008. The lull since then is the longest since the three-year gap between Hurricane Irene in October 1999 and Hurricane Lili in October 2002. Recently updated forecasts for the 2011 hurricane season call for 16 named storms, nine hurricanes and five major hurricanes (those of Category 3 or higher). So far there have been nine named storms and one hurricane.

This story was provided by SPACE.com, sister site to LiveScience.com. Follow SPACE.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

Atmospheric researchers tend to agree that tropical cyclones of unusual ferocity are coming this century, but the strange fact is that there is no consensus to date on the five-point scale used to classify the power of these anticipated storms. In what may sound like a page from the script of the rock-band spoof Spinal Tap with its reference to a beyond-loud electric guitar amplifier volume 11, there is actually talk of adding a sixth level to the current Saffir-Simpson hurricane scale, on which category 5 intensity means sustained winds higher than 155 miles per hour (250 kilometers per hour) for at least one minute, with no speed cap.

The lack of an upper limit on the scale results in all of the most intense tropical cyclones getting lumped together, despite their wide range of power. Category 5 becomes less descriptive when it includes 2005's Emily, which reached peak wind speeds of 257.5 kph (160 mph) and six hours in category 5; the same year's Katrina which held peak wind velocity of 280 kph (175 mph) for 18 hours in the category; and 1980's Allen, churning with peak winds at 305 kph (190 mph) maintained for 72 hours in the highest category.

And now the ferocity forecast for the century adds to this classification problem. "The severe hurricanes might actually become worse. We may have to invent a category 6," says David Enfield, a senior scientist at the University of Miami and former physical oceanographer at the U.S. National Oceanic and Atmospheric Administration (NOAA). This new level wouldn't be an arbitrary relabeling. Global satellite data from the past 40 years indicate that the net destructive potential of hurricanes has increased, and the strongest hurricanes are becoming more common—especially in the Atlantic. This trend could be related to warmer seas or it could simply be history repeating itself. Data gathered earlier than the 1970s, although unreliable, show cycles of quiet decades followed by active ones. The quiet '60s, '70s and '80s ended in 1995, the year that brought Felix and Opal, among others, and resulted in $13 billion in damages and more than 100 deaths in the U.S.

The pros and cons of categories: Five or six?

The average difference between the current categories equals nearly 20 mph, so a category 6 label would likely be applied to hurricanes with sustained winds over (280 kph) 175 mph. The speed and destruction of  hypothetical "category 6" storms is speculative, despite the hurricanes with winds at that level.

After all, meteorologists and climate researchers may not even choose a category 5 storm from the record books if asked to identify the most powerful tropical cyclone in history, because the Saffir–Simpson scale fixates on maximum wind speed lasting for at least one minute and disregards the many other large-scale components that factor into a storm's level of devastation. The whole index should be thrown out the hurricane-proof window, some say.

"If I could do it, I would do away with categories," says Bill Read, director of NOAA's National Hurricane Center (NHC). "The whole indexing [of hurricanes] was done back in the '60s and '70s when we had no way to convey the variables of damage that the storm did. We didn't measure it that carefully; we didn't have the tools."

Even nowadays, instruments to measure actual wind speed are often destroyed during extreme storms, so estimates have to be extrapolated from satellite images and other data. Actual observations can also be suspect. It took 14 years for the World Meteorological Organization to acknowledge that an anemometer in Australia recorded a world record wind speed of 407 kph (253 mph) during Tropical Cyclone Olivia in 1996. Wind speed science has improved over the years. Since the 1990s direct wind measurements from hurricane-hunter aircraft have replaced central pressure measurements, which were often a proxy for wind speeds.

Variables used by meteorologists and climatologists to assess damage can go beyond wind speeds to include duration over land and the extent of deadly storm surges. Read sums it up this way: "Size matters: Katrina, Rita, Ike—all of them made landfall at a 2 or 3 level, but look at the damage they caused. Obviously a category did not accurately describe the impact."

A transition to "impact forecasting" began last year when NOAA's National Hurricane Center simplified the Saffir–Simpson hurricane scale and renamed it the Saffir–Simpson hurricane wind scale. This change involved stripping away the scale's former central pressure, flooding and storm surge estimates. These factors among others are now forecast separately. In 2009 the National Weather Service began using new probability models that provide storm surge estimates ranging from 0.6 to 7.6 meters (two to 25 feet).

What the future holds

History keeps us guessing about where and when the next big tropical cyclone will hit on the U.S. Atlantic or Gulf coasts. As for the most powerful hurricane ever, experts are divided. Some say 1998's Gilbert.; an official answer from a NOAA Web site lists three: 1969's Camille, 1980's Allen and 2005's Wilma (the World Meteorological Organization agrees with the latter).

William Gray, professor emeritus of atmospheric science at Colorado State University in Fort Collins and the "grandfather" of annual hurricane season forecasting, picked the category 4 Great Miami Hurricane of 1926. NHC Director Read went with an unnamed Caribbean hurricane from 1780.

The Atlantic hurricane season, which runs from June 1 to November 30 annually, is predicted to produce more and stronger storms than average this year, although active years have been the norm since 1995. That year the Atlantic entered a period of warm sea-surface temperatures of what is called the Atlantic Multi-Decadal Oscillation, and such cycles typically last two to three decades.

"If the future is like the past, we should have another 10 to 15 years of this active period," Gray says.

This oscillation means the Atlantic is expected to cool in the future, obscuring links among hurricane activity and global warming. Perhaps counterintuitively, recent computer modeling studies predict fewer tropical cyclones if the ocean heats up further as a result of global warming. But they also predict intensification of the ones that do form, albeit with limited confidence. Frequency drops by 6 to 34 percent this century, according to 2010 review article in Nature Geoscience, whereas intensity rises 2 to 11 percent. (Scientific American is part of Nature Publishing Group.)

Today, water is a bigger concern than the wind when it comes to property destruction and loss of life. Look for more emphasis on storm surges in future forecasts, because it is the main reason why evacuations become necessary. Many planners suggest following Read's prescription: "In the U.S. 'Run from the water, hide from the wind' is pretty good, simple advice."

As for the addition of a new category 6, Read insists it is not needed. "I'd be totally opposed to that, even if they did get stronger," he says. "I'll fight 'em tooth and nail under my regime. We'll keep what we have now, but I'm going to focus more on the impacts."

This article was first published at ScientificAmerican.com. © ScientificAmerican.com. All rights reserved.