Nutria Bodies

Piles of nutria carcasses line beaches in Mississippi after Hurricane Isaac flooded the invasive rodents' marsh habitats.

Dead Nutria

Tens of thousands of drowned nutria have washed up on beaches in Mississippi after Hurricane Isaac.

Nutria Washed Ashore

Clean-up crews are removing the rotting nutria carcasses with pitchforks and front-end loaders. The smell is reportedly terrible.

Dead Nutria

Mississippi officials estimate that there could be as many as 20,000 dead nutria (several tons' worth) washing ashore.

Nutria Family

Also called coypu, nutria (Myocastor coypus) were introduced to every continent except Antarctica and Australia from South America, according to the USGS. Though the semi-aquatic rodents are viewed as pests by many, as they destroy large swaths of marsh vegetation and crops, they are valued for their fur in some regions. It was partly this interest in their fur that led to their spread throughout the world.

Nutria

Weighing on average 12 to 15 pounds (though they can get as large as 20 pounds), nutria are like giant rats. They sport large front teeth and forepaws with four clawed toes and a non-functional toe; their hind feet are tipped with 5 clawed toes, four of which are webbed to help the rodents move through their watery homes.

Nutria Corpses

Nutria corpses dot the shoreline in this image from a Mississippi Department of Environmental Quality field worker.

Dead Nutria

Officials expect more nutria to wash ashore in the next several days.

Dead Nutria

Nutria are invasive species that live in marshlands along the Gulf Coast.

As Tropical Storm Isaac roars over Louisiana and elsewhere on the Gulf Coast, it threatens to disrupt a fragile environment that's still recovering from BP's Deepwater Horizon oil spill in the summer of 2010.  

By disturbing the sediments in which the spilled oil is buried, near the beach and deeper in the water, the hurricane could release large quantities of oil, several researchers warn.

"This is another disaster on top of the hurricane that we're going to have to deal with," Garret Graves, chairman of Louisiana's Coastal Protection and Restoration Authority, told the Huffington Post. "The threat is not insignificant."

So far there have been no reports of oil, but that isn't surprising considering most everybody is taking shelter or has evacuated the area, said Lt. Alyssa Johnson, operation officer at the National Response Center, a federal organization responsible for coordinating a response plan to environmental releases of oil or other hazardous materials. [Latest News on Isaac]

Storm surge

Isaac's storm surge, expected to reach heights of 6 to 12 feet (about 2 to 3.5 meters), could transport oil inland, where it could further affect marshlands and wildlife or come into contact with people, Graves told the Bloomberg news service. It also could flood areas containing contaminants such as pesticides, fertilizers and septic system bacteria and wash these back out into coastal waters or into groundwater, University of Florida researcher Andrew Zimmerman told OurAmazingPlanet in an email.

But it's unclear how much oil remains in Gulf sediments and along the shoreline — and how much might be stirred up.

"It could be a lot or a little," said University of Florida researcher Andrew Zimmerman.

An estimated 1 million gallons of MC 252 oil from the Deepwater Horizon spill has been distributed throughout the sediment underwater, on the beach and in marshes, according to Nanciann Regalado, speaking a spokesperson at the U.S. Department of the Interior.

"After danger to humans has passed and field teams can get into the field, samples of oil that has been exposed will be taken," Regalado told OurAmazingPlanet. If chemical analysis finds that the oil was from the Deepwater Horizon, BP may be required to clean up the oil, she added.

Exactly how far below the surface sediment and oil can be disturbed by a hurricane isn't clear, but meteorologist Jeff Masters said large hurricanes can create currents capable of mobilizing whatever oil is at the bottom. 

Nick Shay, a professor of meteorology and physical oceanography at the University of Miami, told the Huffington Post this was possible. Hurricanes can "bring whatever is near the bottom up higher in the water column, and currents can then push it towards the coast," he said.

Erosion

Isaac also could worsen erosion in the area by pounding the shore with waves. According to the National Hurricane Center, Isaac is likely to cause significant erosion of 89 percent of Mississippi's beaches.

 The Deepwater Horizon disaster began with a deadly blowout on April 20, 2010, and spilled an estimated 205 million gallons of crude into the Gulf. Among other damage, the oil killed marsh grasses that prevent erosion. For 18 months afterward, marsh erosion rates doubled to 10 feet (3 meters) per year, said University of Florida researcher Brian Silliman.

Most of the grass has grown back, but how it will weather this storm is unclear. Barrier islands and coastlines could be eroded, affecting nesting areas for many kinds of wildlife, including birds and turtles.

Biggest impact

The biggest environmental impact of Isaac will be erosion causing the loss of wetlands, Masters said. A 2011 study by the United States Geological Survey found that four hurricanes in the past seven years — Katrina, Rita, Gustav and Ike — together destroyed about 250 square miles (650 square kilometers) of Louisiana. "I expect Isaac will destroy 50-100 square miles of wetlands," or about 130 to 260 square kilometers, Masters told OurAmazingPlanet.

A spokesman for BP said the company isn't worried about Isaac. "Consistent with the past two hurricane seasons, we do not expect any significant impact of residual MC 252 oil following Hurricane Isaac," Ray Melick told the Huffington Post.

Although plants and animals are well-adapted to storms like this, Zimmerman said, they have a lowered ability to cope when they are already stressed from human activities.

Luckily, Regalado said, bird nesting season in the area is largely finished and most wintering birds haven't arrived. However, loggerhead sea turtle nesting season is in full swing, and many nests are at risk of flooding.

Reach Douglas Main at dmain@techmedianetwork.com. Follow him on Twitter @Douglas_Main. Follow OurAmazingPlanet on Twitter @OAPlanet. We're also on Facebook and Google+.

Hurricane Isaac is pummeling the Gulf Coast, lashing the area with punishing wind, rain and floods, and because the storm is moving slowly, beleaguered residents can't expect much relief anytime soon, forecasters say.

The storm is creeping northwestward at about 6 mph (9 kph), and is likely to maintain a similar pace for the next 24 to 48 hours, said Tim Schott, a meteorologist at National Weather Service headquarters in Silver Spring, Md.

"It is a slow mover," Schott told OurAmazingPlanet. "Although I don't think it will set any records," he added.

Hurricane Isaac made landfall on the evening of Aug. 28 near the mouth of the Mississippi River as a Category 1 storm packing winds of 80 mph (130 kph).

The hurricane is stuck in a kind of upper-atmospheric doldrums. It's beyond the pull of any large-scale wind patterns, such as the jet stream, so it's plodding along slowly. Once it moves farther inland, toward the middle of the country — jet-stream territory, Schott said — Hurricane Isaac will begin to pick up the pace.

"In general, that is the case," he said. "As [storms] move north, they tend to accelerate." Once they get within reach of the jet stream, they start to speed up.

Hurricanes also typically slow their forward motion a bit once they move over land, and Isaac was no exception. Out over the ocean, the storm was moving at a clip of 14 or 15 mph (22 or 24 kph), but since making landfall, the hurricane has cut its speed by more than half.

As Hurricane Isaac moves northward and picks up speed, it will also weaken. The storms lose steam once they move away from warm ocean waters, which serve as a fuel source.

Adding to the woes of those in its path, Hurricane Isaac is a big storm. (The sheer size of a storm doesn't influence its speed, but it does mean it tends to hammer a wide area.)

"So you take the slow movement and large size of the storm, and people will be impacted for many, many hours," Schott said.

He said the storm is a sobering reminder that a Category 1 hurricane, though the lowest on the Saffir-Simpson Hurricane Scale, can have devastating effects.

Reach Andrea Mustain at amustain@techmedianetwork.com, or follow her on Twitter @AndreaMustain. Follow OurAmazingPlanet on Twitter @OAPlanet. We're also on Facebook & Google+. 

A new satellite image of Hurricane Isaac reveals the storm swirling toward the Louisiana coast, obscuring much of the eastern Gulf of Mexico.

The image was captured at 1:35 p.m. CDT (1735 UTC) on Aug. 28 by the Suomi NPP satellite. The orbiter snapped the image between the hurricane's two landfalls last night. The storm first hit land in Plaquemines Parish, La., at 6:45 p.m. CDT (1145 UTC) and then moved back over water for several hours until 2:15 a.m. CDT (0715 UTC), when it made landfall again near Port Fourchon, La.

The Category 1 hurricane is weakening as it moves inland this morning (Aug. 29). As of 9 a.m. CDT (1400 UTC), the storm's maximum sustained winds were blowing around 75 miles per hour (121 kilometers per hour), according to the National Weather Service (NWS). Water overtopped a levee in Plaquemines Parish, causing major flooding.

The center of Hurricane Isaac is now about 40 miles (64 km) southwest of New Orleans, the NWS reported. The storm is expected to move over Louisiana today and tomorrow, bringing rain to southern Arkansas by Friday.

About the size of a small school bus, Suomi NPP orbits the Earth about 14 times each day, observing nearly the entire planet surface. Among its five instruments, the Visible Infrared Imaging Radiometer Suite (VIIRS) is responsible for the detailed, swirling image of Hurricane Isaac.

Follow Stephanie Pappas on Twitter @sipappas or LiveScience @livescience. We're also on Facebook & Google+. 

Several different satellites are keeping a keen eye on the Hurricane Isaac, which has made landfall along the Louisiana coast nearly seven years to the day after Hurricane Katrina began laying waste to New Orleans.

Imagery from NASA's TRMM and Terra satellites and the GOES-13 spacecraft, operated by the National Oceanic and Atmospheric Administration, showed Hurricane Isaac's outer bands lashing the Gulf Coast earlier today (Aug. 28) before the huge storm came ashore.

Isaac was upgraded from a tropical storm to a Category 1 hurricane today and currently has maximum sustained winds of 80 mph (130 kph). It is predicted to dum perhaps 20 inches (51 centimeters) of rain on some spots over the next few days.

The satellite shots show just how enormous Isaac is. As of this morning, tropical storm-force winds extended 205 miles (330 kilometers) out from Isaac's center, making the maelstrom 410 miles (660 km) wide, NASA officials said.

The Earth-observing spacecraft have been tracking Isaac's progress for a while, watching as it churned across the eastern Caribbean and tacked north toward Florida and the Gulf of Mexico.

The slow-moving maelstrom's trek toward the Gulf Coast is captured in GOES-13 footage from the last three days, which has been compiled into a minute-long video. Viewers can watch as Isaac's center passes 40 miles (64 km) south of Key West, Fla., on the afternoon of Aug. 26, before the storm turns toward the Mississippi Delta.

While experts are predicting heavy rainfall and flooding in Isaac's wake, the damage should not come close to what Hurricane Katrina wrought seven years ago. That storm registered as a Category 3 hurricane when it came ashore on Aug. 29, 2005, with sustained winds topping out around 127 mph (204 kph).

Some experts estimate Katrina caused $125 billion in damage, making it the costliest natural disaster in United States history. The storm killed more than 1,800 people, most of them in Louisiana. Many of these people died after New Orleans' levee system failed and huge swathes of the city were flooded.

This story was provided by SPACE.com, a sister site to OurAmazingPlanet. Follow SPACE.com senior writer Mike Wall on Twitter @michaeldwall or SPACE.com @Spacedotcom. We're also on Facebook and Google+.

Update 7:37 a.m. EDT Wed, Aug. 29: After stalling out over water near the coast after its first landfall, Isaac made its second landfall along the southeast coast of Louisiana just west of Port Fourchon around 2:15 a.m. CDT.

Hurricane Isaac has roared ashore just before 8 p.m. ET in Louisiana's Plaquemines parish.

The storm came ashore as a Category 1 hurricane along the coast of southeastern Louisiana as expected. It made official landfall over a small spit of land near the mouth of the Mississippi River, the Weather Channel has reported. The eye of the storm is back over water and Isaac will make a second landfall tonight.

Isaac's path was eerily similar to that of Hurricane Katrina, which hit seven years ago tomorrow (Aug. 29). Despite the similarities between the storms, there were also considerable differences, including Isaac's comparative weakness.

As it came ashore, Isaac had winds of 80 mph (130 kph). Isaac is expected to weaken as it moves further inland and is cut off from the warm Gulf waters that fuel its convection.

Isaac will continue to dump rain as it moves further inland – rainfalls between 7 and 14 inches (18 to 36 centimeters) are expected.

Isaac became a hurricane — the fourth of the 2012 Atlantic hurricane season — less than a day before it made landfall.

If, sometime in the past few days, you saw a photo alleging to show Hurricane Isaac barreling over ominously still waters as it approached the Gulf Coast, scrub the image from your memory: the photo is fake.

"It is a Photoshopped picture of a supercell thunderstorm that seems to pop up with a new foreground every time there is a hurricane threat anywhere," Bay News 9 meteorologist Josh Linker said.

"I've seen versions of that photo since at least 2005," added Brian McClure, also a meteorologist at the Tampa Bay-based news station.

The current incarnation of the picture claiming to show Isaac was posted to Twitter several days ago, retweeted thousands of times, and even used by some media outlets to accompany its coverage of the storm before the hoax came to light.

Similar fakery occurred last August during Hurricane Irene, when another photo of a supercell thunderstorm, superimposed on a picture of a Florida beach, got retweeted hundreds of thousands of times on Twitter. Likewise, in 2005, supercell storm pictures circulated as alleged shots of Hurricane Katrina making landfall.

Clearly, everyone likes the look of supercells. According to Chris Walcek, a meteorologist at the State University of New York, Albany, these impressive thunderclouds form in the Great Plains when a pocket of hot, vapor-filled air starts to rise in the presence of just the right amount of "wind shear," or change in wind speed with height. The huge air pocket starts to rotate, and the Coreolis force generated by the spin of the Earth enhances the air pocket's rotation.

"[T]he condensation pattern at cloud base forms a 'belt' or 'wall' appearance as air is lifted and sucked into the swirling storm," Walcek told Life's Little Mysteries back in May, when a spectacular supercell was photographed in Texas.

By comparison, tropical storms and hurricanes are much less tightly packed and thus appear less beautifully structured in photographs — at least those taken at ground level. It takes a satellite to capture the terrifying magnificence of a churning hurricane.

Follow Natalie Wolchover on Twitter @nattyover or Life's Little Mysteries @llmysteries. We're also on Facebook & Google+.

People living on the coast are often the first concern when a hurricane strikes. But it's actually the folks farther inland that typically see the most fatalities, due to intense rains causing flash floods and mudslides, as well as tornadoes spawned by tropical cyclones.

More than 60 percent of hurricane-related deaths occur inland and away from the ocean, according to a statement from the University Corporation for Atmospheric Research, based in Boulder, Colo. To help reduce the number of these inland deaths, researchers have created a map to show what areas in the United States are most vulnerable. They created it after examining census data, socio-economic factors, local geography and historical records of hurricane impacts.

Hurricane Floyd in 1999, for example, produced intense winds 1,300 miles (2,100 kilometers) inland. Hurricane Isaac looks likely to produce heavy rains as far north as central Indiana.

The map weighs such socio-economic factors as income level, age and local emergency preparedness.

Poor areas may not be able to deal well with an emergency, for example, if people don't have cars or the resources to quickly vacate their homes, said James Done, a UCAR researcher involved in making the map. Both the elderly and very young are also more vulnerable. These groups were among the most affected by Hurricane Katrina, as they were the least able to evacuate the city after the mandatory order came the day before the monster storm struck.

One of the most vulnerable states, according to the analysis, is Arkansas. That's primarily because the state isn't well-equipped to respond to disasters or to communicate to its citizens what they should do in case of an emergency, Done said. Isaac's projected path is likely to take it over Arkansas, where it could dump substantial amounts of rain.

Another strange result is that areas with more men may be more vulnerable; for unclear reasons, 71 percent of hurricane-related flooding victims are male, according to the release.

The map was made in nine weeks, said Done, primarily by Purdue University graduate student Dereka Carroll. It's an ongoing project and hasn't yet been published in a peer-reviewed journal.

Although the map isn't currently being used by emergency managers, Done said he thinks it could help guide decision-making in the future to save lives.

To see where you stand in terms of vulnerability to hurricanes, check out the map here.

Reach Douglas Main at dmain@techmedianetwork.com. Follow him on Twitter @Douglas_Main. Follow OurAmazingPlanet on Twitter @OAPlanet. We're also on Facebook and Google+.

Tropical Storm Isaac has now officially become Hurricane Isaac, the National Hurricane Center announced this afternoon (Aug. 28).

This strengthening had been expected for more than 24 hours, however — so why did it take so long?

Tropical Storm Isaac was still intensifying early yesterday (Aug. 27) when it encountered a system of dry air, said Tim Schott, a hurricane specialist with the National Oceanographic and Atmospheric Administration. The dry air was sucked into the cyclone and prevented the eye wall (the border surrounding the cyclone's center, or eye) from forming, a key step in a storm's intensification, he told OurAmazingPlanet.

It's also a large storm, with tropical storm force winds extending for nearly 200 miles (320 kilometers). Larger storms sometimes do not intensify as quickly as smaller, more compact cyclones, Schott said.

Furthermore, forecasters still do not understand all the physics that control how or why hurricanes intensify, Schott said.

But whether or not it passed the hurricane threshold doesn't really matter, he said — either way it would be a very large system that will have wide-ranging effects. "Everybody likes to put everything into neat little boxes, but it doesn't matter that it's intensified from 70 to 75 miles per hour. The difference is really not very consequential."

The cyclone finally achieved hurricane strength this afternoon and currently has winds of 75 mph (120 kph), just over the hurricane threshold, according to the National Hurricane Center.

It could intensify slightly in the next 12 to 18 hours, but not by much, according to the NHC. Isaac has limited time and room over ocean waters before it makes landfall, after which it will begin to weaken.

The dry air has weakened the storm's pattern of convection, the rising air that forms the thunderstorms that make up a tropical cyclone. The dry air is still within the system, and may prevent it from strengthening as much as it otherwise would have.

The storm is currently moving to the northwest at 10 mph (16 kph) and the center of the storm could make landfall as early as this evening. It's expected to produce a storm surge between 6 to 12 feet (1.8 to 3.7 meters) in Mississippi and southeastern Louisiana.

As of the latest update from the U.S. National Hurricane Center, Isaac's center was located about 165 miles (260 km) southeast of New Orleans.

A hurricane warning is currently in effect from east of Morgan City, La., to the Mississippi-Alabama border, an area that includes New Orleans. The storm is bearing down on New Orleans seven years to the day after Hurricane Katrina devastated the city.

Hurricane watches and tropical storm warnings and watches have been issued for other areas of the Gulf Coast. The NHC has warned that the impacts from Isaac's storm surge are likely to be significant and that the storm could bring large amounts of rain, as well as the possibility of tornadoes in some places.

Hurricane Isaac is the fourth hurricane of the 2012 Atlantic season.

Reach Douglas Main at dmain@techmedianetwork.com. Follow him on Twitter @Douglas_Main. Follow OurAmazingPlanet on Twitter @OAPlanet. We're also on Facebook and Google+.

As Hurricane Isaac bears down on the city of New Orleans, gaining strength as it churns across the warm, energizing Gulf of Mexico, it conjures memories of another storm that spiraled in its place almost exactly seven years ago: Hurricane Katrina.

With Katrina, we know how the story ended: in devastation, heartbreak and enormous loss of life and property. With Hurricane Isaac, the story has only begun. There are eerie similarities between the storms — their paths, their threat to New Orleans and the time of year — but there are plenty of important ways that Isaac differs from Katrina.

A side-by-side comparison of these hurricanes, and the Gulf Coast's readiness for each of them, can yield insight into how Isaac's story might play out.

Birth date and place

Isaac: Isaac churned to life over ocean waters east of Puerto Rico. The National Hurricane Center named the storm on Aug. 21, making it the ninth named storm of the 2012 Atlantic hurricane season. A storm is named only after it becomes a tropical storm — defined as an organized, rotating storm with maximum sustained winds of at least 39 mph (63 kph).

A tropical storm becomes a hurricane once its top winds hit at least 74 mph (119 kph). Isaac passed that mark midday today (Aug. 28), becoming the fourth hurricane of 2012.

Katrina: Katrina gained strength much more rapidly than Isaac. The storm 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 very next day.

Storm path

Isaac: Almost from the moment it formed, Isaac has chugged toward the U.S. Gulf Coast, aiming for New Orleans. It veered slightly left early on to sweep over Puerto Rico, the Dominican Republic, Haiti and Cuba, but then made a straight shot northwest across the Gulf of Mexico, drenching Florida en route. Isaac's path is projected to take it to a landfall along the southeast coast of Louisiana. It is then projected to move inland over Arkansas and Missouri and then possibly over the northern Midwest.

Katrina: Katrina took a more curvaceous path. The hurricane made landfall in southeast Florida on Aug. 25, then peeled westward through the Gulf of Mexico. It gained strength for a few days from the warm waters, then arced north to the coast.

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

Isaac: Isaac is bigger than most storms, measuring more than 400 miles (644 km) wide as of Aug. 27. (Typical hurricanes measure 300 miles, or 483 km, across.) Isaac's extra girth will mean more rainfall when it bears down on the coast, as well as a strong storm surge, or rise in the seawater level beneath the storm caused by its winds. The National Hurricane Center predicts up to 20 inches (50 centimeters) of rainfall in some places and a storm surge as high as 12 feet (3.5 meters).

Katrina: The 2005 storm was similarly sized. Katrina measured about 400 miles (644 km) wide when it made landfall in Louisiana.

Incidentally, 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

Isaac: Isaac has not grown in intensity as much or as rapidly as predicted. It stayed a tropical storm for a week, then finally reached the status of Category 1 hurricane today, when its maximum sustained winds picked up to 75 mph (121 kph).

Katrina: Katrina was much more intense. In the Gulf of Mexico, Katrina grew into a Category 5 hurricane — the strongest storm category there is. Its maximum sustained winds reached speeds of around 173 mph (278 kph), and then slowed before making landfall. When it hit Louisiana, the storm had been downgraded to a Category 3 hurricane and boasted maximum wind speeds around 127 mph (204 kph), still a major hurricane.

Impact?

Isaac: Isaac has already damaged 2,346 homes, destroyed 335, and caused 24 deaths in Haiti.It is too early to gauge the hurricane's impact on the U.S. Gulf Coast, but some predictions can be ventured.

New Orleans, for one, has probably never been better prepared for a hurricane. Since 2005, the Army Corps of Engineers has spent $14.45 billion overhauling the city's flood prevention system, including raising the height of the levees (sloped embankments), constructing heavily reinforced floodwalls along the canals, and installing a new system of pump stations, including one flood pump capable of sucking 150,000 gallons (more than 560,000 liters) of water per second out of the bowl-like city, should flooding occur.

The rest of the Gulf Coast region may fare less well. Forecasters predict extreme rainfall, and coastal Mississippi, Alabama and Louisiana may experience flooding and destruction of property from flash floods and storm surge. Areas farther inland are also susceptible to flash floods from Isaac's rains, which could total more than 20 inches in some places. However, memories of Katrina have made officials extra cautious, and many areas have been evacuated to prevent loss of life.

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

Isaac: New Orleans Mayor Mitch Landrieu did not issue an evacuation order, but instead called for people outside the city's multibillion-dollar levee system to leave. According to CNN, mandatory evacuations have been ordered for St. Charles Parish and parts of Jefferson and Plaquemines parishes, all in Louisiana.

In Mississippi, mandatory evacuations have been ordered in parts of Hancock and Jackson counties, and port authorities ordered the port cleared of cargo vessels. Finally, in Alabama, Gov. Robert Bentley ordered an evacuation of parts of Baldwin and Mobile counties, while residents in other low-lying or flood-prone areas have been urged to leave voluntarily. The Alabama evacuation orders have since been lifted, according to the Weather Channel, as the threat of Isaac has trended westward.

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. Seven years later, the debate continues about who should bear the brunt of blame for this evacuation failure.

This story was provided by Life's Little Mysteries, a sister site to LiveScience.  Follow Life's Little Mysteries on Twitter @llmysteries. We're also on Facebook & Google+.

While Gulf Coast residents have been warily watching the progress of Tropical Storm Isaac, NASA satellites have been tracking the storm's path and development from above. The latest satellite data show that Isaac is consolidating, a mark of a strengthening storm.

The Atmospheric Infrared Sounder (AIRS) instrument onboard NASA's Aqua satellite acts like an "infrared eye" for storm watchers providing temperature data on Isaac's clouds and the ocean waters around the storm. Cloud temperatures can indicate whether a storm is strengthening or weakening, and knowing the temperature of the surrounding oceans helps forecasters know whether the storm is moving into an environment that will fuel it farther.

AIRS has been keeping an eye on Isaac's path since last week as it moved through the eastern and central Caribbean Sea, across eastern Cuba and into the Gulf of Mexico.

AIRS data taken yesterday (Aug. 26) showed that the area of strong convection (rising air that forms the thunderstorms that make up a tropical cyclone) in the storm had increased. On Aug. 27, Isaac's center of circulation appeared more rounded on AIRS imagery, according to a NASA statement, indicating the circulation center was becoming more organized — a harbinger of a stronger storm.

The Aqua satellite also captured a visible light image of Isaac as the storm passed over Florida and Cuba. Observations from the GOES-13 satellite provide a "movie" showing Isaac's recent movements.

Tropical Storm Isaac currently has maximum sustained winds of 65 mph (100 kph), about 9 mph (14.5 kph) short of the hurricane threshold. But the storm is expected to strengthen into a hurricane over the next 24 hours, though wind shear has been limiting the storm's development so far today. (Wind shear occurs when winds at different levels in the atmosphere are moving in different directions, which can hamper a storm's development.) The low causing this shear is expected to move away though, which will clear Isaac's path to becoming the fourth hurricane of the 2012 Atlantic hurricane season.

As of the latest update from the U.S. National Hurricane Center, Isaac's center was located about 250 miles (400 kilometers) south of Apalachicola, Fla., and about 310 miles (500 km) southeast of the mouth of the Mississippi River. It is moving in a west-northwestward direction.

A hurricane warning is currently in effect from east of Morgan City, La., to Destin, Fla., an area that includes New Orleans. The storm is bearing down on New Orleans seven years to the day after Hurricane Katrina devastated the city.

Hurricane watches and tropical storm warnings and watches have been issued for other areas of the Gulf Coast. The NHC has warned that the impacts from Isaac's storm surge are likely to be significant and that the storm could bring large amounts of rain, as well as the possibility of tornadoes in some places.

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

UPDATED AUG. 28, 8:50 PM ET: Tropical Storm Isaac became a hurricane today (Tuesday afternoon) and made landfall in the evening in southeastern Louisiana around the mouth of the Mississippi River, near New Orleans. The days-long path of Isaac brought it from the distant reaches of the Atlantic Ocean, through the Caribbean and into the Gulf of Mexico.

Click on the map at left to see the forecast path for Isaac released near the time of landfall. The final location of landfall was well inside the cone of probability that had been predicted since yesterday. Isaac will weaken to a tropical storm (“S” on the map) and then a tropical depression (“D”).

Editor’s Note: This will be the last update to this page. For more on the storm, including Hurricane Isaac images and reports of the how the storm played out, see our Hurricane Isaac News & Features page.

Good forecast

The exact path of a hurricane cannot be predicted, but this forecast went well. Meteorologists with the National Hurricane Center (NHC) use several models to project the track within a cone of possibility.  Each of a half-dozen NHC computer models projects a different likely path, and the cone encompasses the overall best guess.

Forecasters had predicted that storm surges could reach 6 to 12 feet along the storm’s path, with the right side of the storm (as viewed from above) seeing the highest surges. Additional predictions for Isaac’s path as it moves inland, along with watches, warnings and other information, are available at the NHC.

See also a video of Isaac’s path as it formed in the Atlantic, and another video of Isaac’s track in recent days as it churned through the Caribbean and into the Gulf — the whole journey is very similar to that of Hurricane Katrina, which hit New Orleans 7 years ago tomorrow (Wednesday). Also check out this short satellite-based video of Isaac’s storm clouds circling counterclockwise, as all hurricanes do.