Hurricane Center - National Hurricane Information » Hurricane Information

What are Hurricanes?

Hurricane Center — Mon, 22 Aug 2011 19:24:24 +0000

Hurricanes are violent tropical storms with sustained winds of at least 74 mph. They form over warm ocean waters – usually starting as storms in the Caribbean or off the west coast of Africa. As they move westward, they are fueled by the warm waters of the tropics. Warm, moist air moves toward the center of the storm and spirals upward. This releases torrential rains. As updrafts suck up more water vapor, it triggers a cycle of strengthening that can be stopped only when contact is made with land or cooler water.

Hurricane Warnings

Hurricane Center — Mon, 22 Aug 2011 19:21:32 +0000

Tropical Storm Watch – issued when tropical storm conditions may threaten a specific coastal area within 36 hours, and when the storm is not predicted to intensify to hurricane strength.
Tropical Storm Warning – winds in the range of 39 to 73 mph can be expected to affect specific areas of a coastline within the next 24 hours.
Hurricane Watch – a hurricane or hurricane conditions may threaten a specific coastal area within 36 hours.
Hurricane Warning – a warning that sustained winds of 74 mph or higher associated with a hurricane are expected in a specified coastal area in 24 hours or less.

Hurricane Terms

Hurricane Center — Mon, 22 Aug 2011 19:20:58 +0000

Tropical Depression – an organized system of clouds and thunderstorms with a defined circulation and maximum sustained winds of 38 mph (33 knots) or less.
Tropical Storm – an organized system of strong thunderstorms with a defined circulation and maximum sustained winds of 39 to 73 mph (34-63 knots).
Hurricane - a warm-core tropical cyclone with maximum sustained winds of 74 mph (64 knots) or greater.
Eye - center a a hurricane with light winds and partly cloudy to clear skies. The eye is usually around 20 miles in diameter, but can range between 5 and 60 miles.
Eye Wall – location within a hurricane where the most damaging winds and intense rainfall are found.
Severe Thunderstorm – a thunderstorm with winds 58 mph or faster or hailstones three-quarters of an inch or larger in diameter.
Tornadoes - violent rotating columns of air that touch the ground; they are spawned by large severe thunderstorms. They can have winds estimated from 100 to 300 mph.
Tornado Watch - tornadoes and severe thunderstorms are possible.
Tornado Warning – tornadoes are detected in your area. Take shelter!

Hurricane Scale

Hurricane Center — Mon, 22 Aug 2011 19:19:49 +0000

Category I – 74-95 mph winds with 4-5 ft. storm surge and minimal damage
Category II – 96-110 mph winds with 6-8 ft. storm surge and moderate damage
Category III – 111-130 mph winds with 9-12 ft. storm surge and major damage
Category IV – 131-155 mph winds with 13-18 ft. storm surge and severe damage
Category V – 155+ mph winds with 18+ ft. storm surge and catastropic damage

What to do when warnings are issued

Hurricane Center — Mon, 22 Aug 2011 19:17:46 +0000

What to do when a Hurricane Watch is issued:
• Monitor radio and TV broadcasts for information regarding the storm’s progress.
• Fuel-up the family or rental car.
• Refill prescriptions for your family and pets, ensuring at least a two-week supply.
• Get cash, since ATMs and banks may run out of money before the storm or not be operational following the storm.
• Review your plans. Find out if you will be forced to evacuate where you are staying if the storm threatens your area. Locate evacuation routes which will take you inland to save shelter.
What to do when a Hurricane Warning is issued:
• Monitor radio and TV broadcasts for storm advisories and evacuation announcements.
• Gather belongings in case of evacuation order.
What to do if an evacuation order is issued:
• Leave immediately.
• Take any survival supplies you may have such as bottled water.
• Take medicines and/or special needs equipment.
• Pet, alcoholic beverages, and weapons are NOT allowed in shelters.
• Stay calm and take your time. Traffic will be heavy and move slowly, but there is sufficient time to reach safety.

Top 10 Most Vulnerable Areas to Hurricanes

Hurricane Center — Mon, 16 May 2011 21:06:45 +0000

According to Dr. Stephen P. Leatherman, Director of the International Hurricane Research Center, the top 10 most vulnerable areas to hurricanes are:

New Orleans, Louisiana
Lake Okeechobee, Florida
Florida Keys
Coastal Mississippi
Miami/Ft. Lauderdale, Florida
Galveston/Houston, Texas
Cape Hatteras, North Carolina
Eastern Long Island, New York
Wilmington, North Carolina
Tampa/St. Petersburg, Florida

While New Orleans would at first seem not to be a surprise, many might think that spots in Florida actually see more hurricane activity. And this, in fact, may be true. But an important point to remember here is that this is a list of the “most vulnerable” spots. Therefore, New Orleans, with its “below sea level” status and its levee system, makes it especially susceptible to flooding and damage when a hurricane actually does hit. And, of course, the world was witness to just what can happen to a city like New Orleans when Hurricane Katrina struck.

In keeping with this theme, Lake Okeechobee, Florida is the only other major area that is protected by levees. And so this is why they get the number two spot. There are approximately 40,000 people living at the base of Hoover Dike in the Lake Okeechobee area – which, according to reports, is leaking.

There were twelve criteria used to determine a location’s vulnerability to a hurricane. Hurricane frequency and intensity, as well as potential levee or dike failure, were the main determinants. Some of the other factors included the potential for freshwater flooding, island breaching history, costal erosion history, the amount of actual residents potentially at risk, the quality and distance of evacuation routes, and the ability of local and state governments and organizations to respond to the damage a hurricane inflicts.

Locations in Florida, as is probably expected, took three out of the top five spots, and then added a fourth at number ten – the Tampa/St. Petersburg area. With coasts on both the Atlantic Ocean and the Mexican Gulf, they are in a unique position of possibly getting hit from different directions.

While a place like Long Island may come as a surprise to many, the area has been actually impacted in the not-so-distant past by Hurricane Donna (1960), Hurricane Gloria (1985), and Hurricane Bob (1991).

What is the Difference Between a Hurricane and a Typhoon?

Hurricane Center — Mon, 16 May 2011 20:54:08 +0000

According to the Atlantic Oceanographic and Meteorological Laboratory, a “hurricane” and a “typhoon” are simply different names for a “tropical cyclone.” As a general rule, these cyclones are given the name “hurricane” in the Western hemisphere (the North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline, or the South Pacific Ocean east of 160E), and the term “typhoon” is applied in the Eastern hemisphere (the Northwest Pacific Ocean west of the dateline).

That said, there are even further distinctions throughout the world. The term “severe tropical cyclone” is given in the Southwest Pacific Ocean west of 160E or Southeast Indian Ocean east of 90E. The term “severe cyclonic storm” is given in the North Indian Ocean. And the term “tropical cyclone” is given in the Southwest Indian Ocean.

When the maximum sustained surface winds of a tropical cyclone is less than 39 miles per hour (34 kt, 17 m/s), it is referred to as a “tropical depression.” In the area between this 39 mph (34 kt, 17 m/s) mark and 74 mph (64 kt, 33 m/s), it is known as a “tropical storm.” And then, of course, as it reaches the 74 mph mark (64 kt, 33 m/s), it becomes classified as a hurricane, typhoon, or one of the other names mentioned above.