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The Basics
A tropical cyclone is a warm-core, low pressure system without any "front" attached, that develops over the tropical or subtropical waters, and has an organized circulation. Almost all tropical cyclones in the Atlantic basin (which includes the Gulf of Mexico and Caribbean Sea) form between June 1st and November 30th, known as hurricane season. On rare occasions, a tropical disturbance can form a little earlier or later than this. Tropical cyclones are classified in one of three categories:
| Tropical Depression |
Tropical Storm |
Hurricane |
| An organized system of clouds and thunderstorms with a defined circulation, and maximum sustained winds of 38 mph (33 knots) or less. |
An organized system of strong thunderstorms with a defined circulation and maximum sustained winds of 39 mph to 73 mph (34-63 knots). |
An intense tropical weather system with a well-defined circulation, producing maximum sustained winds of 74 mph (64 knots) or greater. |
Hurricanes are further classified by their wind speed, using the Saffir-Simpson Hurricane Scale. The stronger the wind, the higher the category given, and the more damage the hurricane can cause. A major hurricane is defined as a category 3 or higher hurricane. The following table describes the 5 categories of hurricanes and the damages as a result of the strong wind.
| Cat. |
Speed |
Damage |
| 1 |
| 74-95 |
mph |
| 64-82 |
kts |
| 119-153 |
km/hr |
|
No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Some damage to poorly constructed signs. |
| 2 |
| 96-110 |
mph |
| 83-95 |
kts |
| 154-177 |
km/hr |
|
Some roofing material, door, and window damage of buildings. Considerable damage to shrubbery and trees with some trees blown down. Considerable damage to mobile homes, poorly constructed signs, and piers. |
| 3 |
| 111-130 |
mph |
| 96-113 |
kts |
| 178-209 |
km/hr |
|
Some structural damage to small residences and utility buildings with a minor amount of curtainwall failures. Damage to shrubbery and trees with foliage blown off trees and large tress blown down. Mobile homes and poorly constructed signs are destroyed. |
| 4 |
| 131-155 |
mph |
| 114-135 |
kts |
| 210-249 |
km/hr |
|
More extensive curtainwall failures with some complete roof structure failures on small residences. Shrubs, trees, and all signs are blown down. Complete destruction of mobile homes. Extensive damage to doors and windows. |
| 5 |
| Greater than |
| 155 |
mph |
| 135 |
kts |
| 249 |
km/hr |
|
Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. All shrubs, trees, and signs blown down. Complete destruction of mobile homes. Severe and extensive window and door damage. |
The word hurricane comes from the Carib Indians of the West Indies, who called this storm a huracan. Supposedly, the ancient Tainos tribe of Central America called their god of evil "Huracan". Spanish colonists modified the word to hurricane.
Tropical Cyclone Formation
Tropical cyclones form in the warm waters of tropical and sub-tropical oceans, seas, or Gulf of Mexico with some areas are more prone to development at certain times of season. Click on image to enlarge.
June
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July
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August
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September
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October
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November
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Most hurricanes evolve from tropical disturbances. A tropical disturbance is a discrete system of organized convection (showers or thunderstorms), that originate in the tropics or subtropics, does not migrate along a frontal boundary, and maintains its identity for 24 hours or more. The seedlings of hurricanes can come from:
- Easterly Waves: Also called tropical waves, this is an inverted trough moving generally westward in the tropical easterlies. A trough is defined as a region of relative low pressure. The majority of hurricanes form from easterly waves.
- West African Disturbance Line (WADL): This is a line of convection (similar to a squall line) which forms over West Africa and moves into the Atlantic Ocean. WADL's usually move faster than tropical waves.
- TUTT: A TUTT (Tropical Upper Tropospheric Trough) is a trough, or cold core low in the upper atmosphere, which produces convection. On occasion, one of these develops into a warm-core tropical cyclone.
- Old Frontal Boundary: Remnants of a polar front can become lines of convection and occasionally generate a tropical cyclone. This will occur early or late in the hurricane season in the Gulf of Mexico or Caribbean Sea.
Once a disturbance forms and sustained convection develops, it can become more organized under certain conditions. If the disturbance moves or stays over warm water (at least 80°F), and upper level winds remain weak, the disturbance can become more organized.
When a tropical depression forms, it is identified by a number identical to the number of depressions which have formed during the hurricane season. When a tropical depression intensifies to a tropical storm (wind 39-73 mph), it is given a name, and this name is kept if and when the storm intensifies into a hurricane.
Tropical Cyclone Names
The first tropical storm is given a name starting with "A", the next storm "B" and so on through the alphabet. The names alternate between male and female names. Moreover, the names reflect the three main languages of the area: English, Spanish and French. The same names are repeated every five years. On occasion, an extremely powerful and/or destructive hurricane will have its name retired.
Below is the list of the Atlantic Tropical Storm Names.
| 2004 |
2005 |
2006 |
2007 |
2008 |
2009 |
Alex
Bonnie
Charley
Danielle
Earl
Frances
Gaston
Hermine
Ivan
Jeanne
Karl
Lisa
Matthew
Nicole
Otto
Paula
Richard
Shary
Tomas
Virginie
Walter |
Arlene
Bret
Cindy
Dennis
Emily
Franklin
Gert
Harvey
Irene
Jose
Katrina
Lee
Maria
Nate
Ophelia
Philippe
Rita
Stan
Tammy
Vince
Wilma |
Alberto
Beryl
Chris
Debby
Ernesto
Florence
Gordon
Helene
Isaac
Joyce
Kirk
Leslie
Michael
Nadine
Oscar
Patty
Rafael
Sandy
Tony
Valerie
William |
Allison
Barry
Chantal
Dean
Erin
Felix
Gabrielle
Humberto
Iris
Jerry
Karen
Lorenzo
Michelle
Noel
Olga
Pablo
Rebekah
Sebastien
Tanya
Van
Wendy |
Arthur
Bertha
Cristobal
Dolly
Edouard
Fay
Gustav
Hanna
Isidore
Josephine
Kyle
Lili
Marco
Nana
Omar
Paloma
Rene
Sally
Teddy
Vicky
Wilfred |
Ana
Bill
Claudette
Danny
Erika
Fred
Grace
Henri
Ida
Joaquin
Kate
Larry
Mindy
Nicholas
Odette
Peter
Rose
Sam
Teresa
Victor
Wanda |
How to know if a tropical cyclone threatens your area.
Listen to your NOAA Weather Radio and check the Tropical Weather Update. Four times a day during the hurricane season, the National Weather Service's Tropical Prediction Center (TPC) issues a product called the Tropical Weather Outlook. This product discusses the location of tropical disturbances and cyclones, along with a forecast movement and intensification, weakening or dissipation. If a tropical cyclone threatens your area, your local National Weather Service Office will broadcast the vital information on the NOAA Weather Radio.
Next: Tropical Cyclone Hazards - Storm Surge
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Page last modified: July 27, 2004 |
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