Whipping winds, torrential downpours, power outages and floods — hurricane season in the Atlantic brings a host of dramatic and dangerous weather with it.
But when exactly does the Atlantic hurricane season start and how long does it last? And what can people do to prepare in the face of the most dangerous storms on Earth? From hurricane naming conventions to staying safe in a storm, we'll detail all you need to know about the upcoming hurricane season.
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How they form
Hurricanes are the most violent storms on Earth, according to NASA. At heart, hurricanes are fueled by just two ingredients: heat and water. Hurricanes are seeded over the warm waters above the equator, where the air above the ocean's surface takes in heat and moisture. As the hot air rises, it leaves a lower pressure region below it. This process repeats as air from higher pressure areas moves into the lower pressure area, heats up, and rises, in turn, producing swirls in the air, according to NASA. Once this hot air gets high enough into the atmosphere, it cools off and condenses into clouds. Now, the growing, swirling vortex of air and clouds grows and grows and can become a thunderstorm.
So, the first condition needed for hurricanes is warmer waters in the Atlantic Ocean, which cause a number of other conditions favorable to hurricanes.
"When the waters are warmer, it tends to mean you have lower pressures. It means a more unstable atmosphere, which is conducive to hurricanes intensifying," said Phil Klotzbach, an atmospheric scientist at Colorado State University. "These thunderstorms, which are the building blocks of hurricanes, are better able to organize and get going."
Another key factor: wind shear, or the change in wind direction with height into the atmosphere, Klotzbach said.
"When you have a warm tropical Atlantic, you have reduced levels of wind shear," Klotzbach told Live Science. "When you have a lot of wind shear it basically tears apart the hurricane."
(Storms that form on different sides of the equator have different spin orientations, thanks to Earth's slight tilt on its axis, according to NASA.)
The individual ingredients for hurricanes, however, don't pop up at random; they are guided by larger weather systems.
"There are two dominant climate patterns that really control the wind and pressure patterns across the Atlantic," said Gerry Bell, the lead seasonal hurricane forecaster for NOAA's Climate Prediction Center in Washington, D.C.
The first is the El Niño/La Niña cycle. During an El Niño, in which ocean water around the northwestern coast of South America becomes warner than usual, Atlantic hurricanes are suppressed, while La Niña creates more favorable conditions for hurricanes, Bell said.
The second climate pattern is the Atlantic Multidecadal Oscillation (AMO), which is, as the name implies, a trend that lasts anywhere from 25 to 40 years and is associated with warmer waters in the Atlantic and stronger African monsoons, Bell said.
"When this pattern is in its warm phase, or a warmer tropical Atlantic Ocean, we tend to see stronger hurricane patterns for decades at a time," Bell told Live Science.
A warm-phase AMO conducive to hurricanes prevailed between 1950 and 1970 and since 1995, Bell said.
2017 hurricane outlook
Officially, the Atlantic hurricane season starts on June 1 and will run until Nov. 30. In the Eastern Pacific Ocean, hurricane season begins May 15 and ends Nov. 30, according to the National Weather Service. However, most of these storms hit during peak hurricane season between August and October, on both coasts, according to the National Weather Service's Climate Prediction Center.
The Climate Prediction Center releases its hurricane season forecast in late May every year. To make the predictions, scientists analyze a host of factors, from wind speed to sea surface temperatures. Because the El Niño/La Niña cycle typically materializes in summer or early fall, forecasts done too early have limited meaning, Bell said. [A History of Destruction: 8 Great Hurricanes]
The Climate Prediction Center classifies hurricane seasons as above-normal (between 12 and 28 tropical storms and between seven and 15 hurricanes); near-normal (Between 10 and 15 tropical storms and between four and nine hurricanes) and below-normal (Between four and nine tropical storms and two to four hurricanes).
The Climate Prediction Center released its 2017 hurricane outlook on May 25. This year is likely to be an above-normal hurricane season for the Atlantic. The region has a 70 percent chance of experiencing between 11 and 17 storms with sustained winds of 39 mph (62 km/h) or higher. Between five and nine of these storms may become hurricanes, or storms with sustained winds of 74 mph (119 km/h) or higher. And anywhere from two to four of these storms could become major-category 3, 4 or 5 hurricanes, which means they would have sustained winds of 111 mph (178 km/h) or higher.
However, because the predictions for El Niño are still uncertain early in the season, the forecast has considerable uncertainty. The CPC currently predicts a 45 percent chance of an above-normal hurrican season, a 35 percent chance of a normal or near-normal hurricane season, and a 20 percent chance of a below-normal season. As El Niño's fate becomes more certain later in the season, and peak hurricane intensity arrives in the Atlantic, the picture will become clearer, according to NOAA.
"We update the seasonal outlooks in early August to coincide with this onset of the peak season," Bell said.
Tropical storm categories
Once a storm has wind speeds of 38 mph (58 km/h), it is officially a tropical storm. At 74 mph (119 km/h), the storm has reached hurricane levels.
At that point, scientists use a 1 to 5 scale known as the Saffir-Simpson Hurricane Wind Scale to classify hurricane strength, with category 1 being the least severe hurricanes and category 5 being the strongest. Some scientists have also proposed adding a category 6 to account for storms that are well beyond the highest sustained wind speed for a category 5 hurricane.
Sustained wind speed (mph)
Minimal, with some roof leakage, gutter damage, snapped tree branches and toppled trees with shallow roots
Moderate, with major roof and siding damage; uprooted trees could block roads; power loss possible for days to weeks
Devastating damage, with gable and decking damage, many more uprooted trees and extended power outages
Catastrophic damage; roofs and exterior walls will be destroyed; trees will snap; power outages for weeks to months. Large area uninhabitable for weeks or months
157 or higher
High fraction of framed houses will be destroyed; power outages for weeks to months; and huge swaths uninhabitable for same period
Source: NOAA's National Hurricane Center
Some scientists have argued against using just wind speed as a metric to determine a storm's severity and potential damage, arguing that other metrics such as storm surge height or rainfall could provide better insight into a storm's ferocity. However, the National Hurricane Center (NHC) has argued that metrics like storm surges can be hard to predict because local differences in the shape of the terrain of the ocean floor leading up to the coastline can determine the height of storm surges.
Hurricanes, tropical storms and typhoons refer to the same type of storm, but the nomenclature reveals where they form. Tropical cyclone refers to any storm that formed 300 miles (482 km) south of the equator, whereas hurricanes are storms formed in the Northeast Pacificand Atlantic, typhoons are tropical storms that form in the Northwest Pacific and cyclone is the term used for storms in the South Pacific and Indian Ocean, according to NOAA's ocean service.
How hurricanes are named
Hurricanes initially were named in honor of the feast day for a Catholic saint. For instance, Hurricane San Felipe occurred on Sept. 13, 1876, or the feast day of Saint Phillip, according to the National Hurricane Center. Hurricanes that struck on the same day would be distinguished by a suffix placed on the later one, Live Science previously reported. For example, a storm that struck on Sept. 13, 1928, was dubbed Hurricane San Felipe II, to distinguish it from the 1876 storm.
However, by the 1950s, the naming convention changed and in the U.S., hurricanes were given female names based on the international alphabet, according to the NHC. The practice of calling storms by female names only was abandoned in 1978.
Despite the seemingly open-ended possibilities, meteorologists do not have free reign in deciding names. The World Meteorological Organization (WMO) has a long list of alphabetical storm names that repeats on a six-year cycle. The organization aims for clear and simple names. Names are in English, Spanish, Dutch and French, to account for the many languages spoken by people potentially affected by hurricanes.
"Experience shows that the use of short, distinctive given names in written as well as spoken communications is quicker and less subject to error than the older, more cumbersome, latitude-longitude identification methods. These advantages are especially important in exchanging detailed storm information between hundreds of widely scattered stations, coastal bases and ships at sea," the organization says on its website.
If a storm was so devastating that using the name again would be insensitive, the group meets and agrees to strike the name from the list.
For instance, people don't have to worry about facing the wrath of a Hurricane Katrina, Ike, Hattie or Opal again, because those names have been retired, according to the NHC.
For the 2017 hurricane season, the following hurricane names could come into play in the North Atlantic, Caribbean and Gulf of Mexico, according to the WMO:
How to prepare
Staying safe during the hurricane season starts with a simple step: Have a plan. People can plan for hurricanes using a simple guide at Ready.gov. Plans need to be worked out for all family members. And for those animal lovers out there, Fido and Mr. Whiskers also need an escape plan.
This plan includes figuring out how to determe whether it's safe to hunker down at home during a storm or whether you are in an evacuation zone. If so, there is likely a specific route you should take in the event of an evacuation, as many roads may be closed, Live Science previously reported.
If you are in an evacuation zone, you also need to figure out accommodations during the storm — this could be anything from staying with family and friends to renting a motel to staying in a shelter.
Family members often have trouble reaching each other during hurricanes, so determining a preset meeting place and protocol can be helpful. Sometimes, local cellphone lines are overloaded during a storm, so consider texting. Another alternative is to have a central out-of-state contact who can relay messages between separated family members.
During a storm, pets should be leashed or placed in a carrier, and their emergency supplies should include a list of their vaccinations as well as a photo in case they get lost, according to the Humane Society for the United States. Also important is finding someone who can care for them, in the event that a hotel or shelter does not accept pets. During an emergency, they should also be wearing a collar with the information of an out-of-state contact in case they get separated from you, according to the HSUS.
Storm-proof your home
Anyone who lives in a hurricane-prone area would do well to protect their property in advance of a flood. Because hurricanes often cause their damage when trees fall on property, homeowners can reduce the risk of damage by trimming trees or removing damaged trees and limbs, according to Ready.gov.
Another easy step is to make sure rain gutters are fixed in place and free of debris. Reinforcing the roof, doors and windows, including a garage door, is also important, according to Ready.gov.
Power generators can also be an important tool if the power is cut off for long periods of time. A power generator needs to be kept outside, as they produce dangerous levels of carbon monoxide.
People who are very serious about prevention may even consider building a "safe room" — a fortified room designed to withstand the punishing winds of a tornado or hurricane, according to the Federal Emergency Management Agency pamphlet "Taking Shelter from the Storm: Building a Safe Room for Your Home or Small Business," (FEMA, 2014).
People living in hurricane country also need to have a stash of emergency supplies, ideally placed in multiple locations throughout a dwelling. According to Ready.gov, a basic disaster kit should include:
- A gallon of water per person per day for at least three days
- A three-day supply of non-perishable food
- A battery-powered or hand-crank radio
- A flashlight with extra batteries
- A first aid kit
- A whistle to get help
- Dust mask
- Moist towelettes, garbage cans and plastic ties for sanitation
- A wrench or pliers for turning off busted pipes
- A can opener for food
- And cellphone chargers
Originally published on Live Science.