Hurricane Facts

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Defining a Hurricane

A Hurricane is a type of tropical cyclone – the general term for all circulating weather systems (counterclockwise in the Northern Hemisphere) over tropical waters. Tropical cyclones are classified as follows:

1. Tropical Depression -- An organized system of clouds and thunderstorms with a defined circulation and maximum sustained winds of 38 mph (33 knots) or less.

2. Tropical Storm -- An organized system of strong thunderstorms with a defined circulation and maximum sustained winds of 39 to 73 mph (34-63 knots).

3. Hurricane -- An intense tropical weather system with a well-defined circulation and maximum sustained winds of 74 mph (64 knots) or higher. In the western Pacific, hurricanes are called “typhoons,” and similar storms in the Indian Ocean are called “cyclones.”

Hurricanes are products of the tropical ocean and atmosphere. Powered by heat from the sea, they are steered by the easterly trade winds and the temperate westerlies as well as by their own ferocious energy. Around their core, winds grow with great velocity, generating violent seas. Moving ashore, they sweep the ocean inward while spawning tornadoes and producing torrential rains and floods.

Each year on average, ten tropical storms (of which six become hurricanes) develop over the Atlantic Ocean, Caribbean Sea, or Gulf of Mexico. Many of these remain over the ocean. However, about five hurricanes strike the United States coastline every three years. Of these five, two will be major hurricanes (category 3 or greater on the Saffir-Simpson Hurricane Scale).

Source: U.S. DEPARTMENT OF COMMERCE , NOAA, National Weather Service

Terms to Know

By international agreement, tropical cyclone is the general term for all cyclone circulations originating over tropical waters, classified by form and intensity as follows:  

Source: U.S. DEPARTMENT OF COMMERCE , NOAA, National Weather Service

 

 Hurricane Scale

         All Hurricanes are dangerous, but some are more so than others. The way storm surge, wind and other factors combine determines a 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. This can be used to give an estimate of the potential property damage and flooding expected along the coast with a hurricane.

Saffir-Simpson Hurricane Scale

Category

Definition

Effects

One

Winds 74-95 mph

No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Also, some coastal road flooding and minor pier damage

Two

Winds 96-110 mph

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.

Three

Winds 111-130 mph

Some structural damage to small residences and utility buildings with a minor amount of curtainwall 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 ASL may be flooded inland 8 miles or more.

Four

Winds 131-155 mph

More extensive curtainwall failures with some complete roof structure failure on small residences. Major erosion of beach. Major damage to lower floors of structures near the shore. Terrain continuously lower than 10 feet above sea level (ASL) may be flooded requiring massive evacuation of residential areas inland as far as 6 miles.

Five

Winds greater than 155 mph

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 ASL and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5 to 10 miles of the shoreline may be required.

Source: U.S. DEPARTMENT OF COMMERCE , NOAA, National Weather Service

 

 Be Prepared  

          In preparing for the 2002 Hurricane Season, make plans for action: 

 Hurricane Watch

          In preparing for the hurricane season, the first step is understanding the warnings that are issued by the National Weather Service: 

            A hurricane WATCH means that hurricane conditions MAY threaten an area within 24-36 hours. When a hurricane WATCH is issued, everyone in that area should listen for further advisories and be prepared to act promptly. 

            When a hurricane WATCH is issued, people in the affected area should: 

 

Hurricane Warning

           In preparing for the hurricane season, the first step is understanding the warnings that are issued by the National Weather Service: 

A hurricane WARNING is issued when hurricane conditions are expected in a specified coastal area in 24 hours or less. Hurricane conditions include winds of 74 miles an hour (64 knots) and/or dangerously high tides and waves.  

Actions for protection of life and property should begin immediately when the warning is issued, including:  

 Family Emergency Supplies

Have these items in your residence – and ready to go if you are forced to evacuate: 


Family Response Plan  

 

 Weathering the Storm 

If you are traveling, find safe shelter immediately.  

If you are at home or at work: 

 If winds become strong:           

 

 Evacuation 

 

Inland Flooding 

            When you hear “hurricane,” think inland flooding: 

 After the Storm