Hurricane Basics - WECT TV6-WECT.com:News, weather & sports Wilmington, NC

Hurricane Basics

A tropical cyclone is a low pressure system that has thunderstorm activity and rotates counterclockwise; a hurricane is the most severe form of this type of meteorological phenomenon. The destructive force of a hurricane extends over a wide area, requiring that precautions be taken far from where the eye is predicted to come ashore. Hurricane-force winds can extend outward to about 25 miles from the storm center of a small hurricane and more than 150 miles for a larger one. The range over which tropical storm-force winds occur is even greater, ranging as far out as almost 300 miles from the eye of a large hurricane. A hurricane's speed and path depend on complex ocean and atmospheric interactions, including the presence or absence of other weather patterns. This complexity makes it very difficult to predict the speed and direction of a hurricane.
Saffir-Simpson Hurricane Scale
All hurricanes are dangerous, but some are more so than others. The way storm surge, wind, and other factors combine determine the hurricane's destructive power. To make comparisons easier, and to make the predicted hazards of approaching hurricanes clearer to emergency forces, National Oceanic and Atmospheric Administration's hurricane forecasters use a disaster potential scale which assigns storms to five categories. Category 1 is a minimal hurricane; category 5 is the worst case.

The category of the storm does not necessarily relate directly to the damage it will inflict. Lower category storms (and even tropical storms) can cause substantial damage depending on what other weather features they interact with, where they strike, and how slow they move.
 
  WINDS STORM SURGE EFFECTS
1 74mph
to
95mph		 4ft
to
5ft		 No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Also, some coastal road flooding and minor pier damage.
2 96mph
to
110mph		 6ft
to
8ft		 Some roofing material, door and window damage to buildings. Considerable damage to vegetation, mobile homes, and piers. Coastal and low-lying escape routes flood 2-4 hours before arrival of center. Small craft in unprotected anchorages break moorings.
3 111mph
to
130mph		 9ft
to
12ft		 Some structural damage to small residences and utility buildings with a minor amount of curtain wall failures. Mobile homes are destroyed. Flooding near the coast destroys smaller structures with larger structures damaged by floating debris. Terrain continuously lower than 5 feet above sea level may be flooded inland 8 miles or more.
4 131mph
to
155mph		 13ft
to
18ft		 More extensive curtain wall failures with some complete roof structure failure on small residences. Major erosion of beach areas. Major damage to lower floors of structures near the shore. Terrain continuously lower than 10 feet above sea level may be flooded requiring massive evacuation of residential areas inland as far as 6 miles.
5 over
155mph		 19ft
to
25ft		 Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. Major damage to lower floors of all structures located less than 15 feet above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5 to 10 miles may be required.
Hurricane Names
Hurricanes began being named so that the storms could easily be referenced without having to use latitude and longitude. This made communication quicker and less prone to error for forecasters, storm trackers, and the public alike. Initially the phonetic alphabet was used to name storms (Able, Baker, Charlie), but in 1953 the nation's weather services began using female names instead. In 1979 male names were added to the lists of storms for the Atlantic and Gulf of Mexico, and this is the naming convention weather services still use today.
2009 2010 2011 2012
Ana
Bill
Claudette
Danny
Erika
Fred
Grace
Henri
Ida
Joaquin
Kate
Larry
Mindy
Nicholas
Odette
Peter
Rose
Sam
Teresa
Victor
Wanda
Alex
Bonnie
Colin
Danielle
Earl
Fiona
Gaston
Hermine
Igor
Julia
Karl
Lisa
Matthew
Nicole
Otto
Paula
Richard

Shary
Tomas
Virginie
Walter
Arlene
Bret
Cindy
Don
Emily
Franklin
Gert
Harvey
Irene
Jose
Katia
Lee
Maria
Nate
Ophelia
Philippe
Rina
Sean
Tammy
Vince
Whitney
 Alberto
Beryl
Chris
Debby
Ernesto
Florence
Gordon
Helene
Isaac
Joyce
Kirk
Leslie
Michael
Nadine
Oscar
Patty
Rafael
Sandy
Tony
Valerie
William
Tropical Classifications
By international agreement, Tropical Cyclone is the general term for all cyclone circulations originating over tropical waters. They are classified by form and intensity as follows:
 
Tropical Wave
A trough of low pressure in the trade-wind easterlies.
 
Tropical Disturbance
A moving area of thunderstorms in the Tropics that maintains its identity for 24 hours or more. A common phenomenon in the tropics.
 
Tropical Depression
A tropical cyclone in which the maximum sustained surface wind is 38 mph (33 knots) or less.
 
Tropical Storm
A tropical cyclone in which the maximum sustained surface wind ranges from 39-73 mph (34-63 knots) inclusive.
 
Hurricane
A tropical cyclone in which maximum sustained surface wind is 74 mph (64 knots) or greater.
 
Small Craft Cautionary Statements
When a tropical cyclone threatens a coastal area, small craft operators are advised to remain in port or not to venture into the open sea.
Hurricane Terminology
 
Tropical Storm Watch
Is issued for a coastal area when there is the threat of tropical storm conditions within 36 hours.
 
Tropical Storm Warning
A warning for tropical storm conditions including sustained winds within the range of 39 to 73 mph (34 to 63 knots) which are expected in a specified coastal area within 24 hours or less.
 
Hurricane Watch
An announcement that hurricane conditions pose a possible threat to a specified coastal area within 36 hours.
 
Hurricane Warning
A warning that sustained winds of 74 mph (64 knots) or higher are expected in a specified coastal area within 24 hours or less.
 
Storm Surge
An abnormal rise of the sea along a shore as the result, primarily, of the winds of a storm.
 
Flash Flood Watch
Means that flash flood conditions are possible within the designated watch area - be alert.
 
Flash Flood Warning
Means a flash flood has been reported or is imminent - take immediate action.
 

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