Basics of Hurricane

What is Hurricane?
Hurricane Safety
Hurricane Names
Saffir-Simpson Hurricane Scale

The ingredients for a hurricane include a pre-existing weather disturbance, warm tropical oceans, moisture, and relatively light winds aloft. If the right conditions persist long enough, they can combine to produce the violent winds, incredible waves, torrential rains, and floods we associate with this phenomenon.

Each year, an average of ten tropical storms develop over the Atlantic Basin (the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico.) Many of these remain over the ocean and never impact the U.S. coastline. On average, six of these storms become hurricanes each year. In an average 3-year period, roughly five hurricanes strike the US coastline, killing approximately 50 to 100 people anywhere from Texas to Maine. Of these, two are typically "major" or "intense" hurricanes.

The official hurricane season for the Atlantic Basin is from 1 June to 30 November. The peak of the season is from mid-August to late October, however, deadly hurricanes can occur anytime in the hurricane season.

What is a Hurricane?

A hurricane is a type of tropical cyclone, which is a generic term for a low pressure system that generally forms in the tropics. The cyclone is accompanied by thunderstorms and, in the Northern Hemisphere, a counterclockwise circulation of winds near the earth's surface. Tropical cyclones are classified as follows:

An organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds* of 38 mph (33 kt**) or less.

An organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds of 39-73 mph (34-63 kt).

An intense tropical weather system of strong thunderstorms with a well-defined surface circulation and maximum sustained winds of 74 mph (64 kt) or higher.

Hurricanes are categorized according to the strength of their winds using the Saffir-Simpson Hurricane Scale. A Category 1 storm has the lowest wind speeds, while a Category 5 hurricane has the strongest. These are relative terms, because lower category storms can sometimes inflict greater damage than higher category storms, depending on where they strike and the particular hazards they bring. In fact, tropical storms can also produce significant damage and loss of life, mainly due to flooding.

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Hurricane Safety

During a hurricane or serious tropical storm it is important to know what to do to keep yourself and your family safe. The National Hurricane Center has resources to help you be prepared.

Know if you live in an evacuation area. Know your home's vulnerability to storm surge, flooding and wind. Have a written plan based on this knowledge.

At the beginning of hurricane season (June 1st), check the supplies for your disaster supply kit, replace batteries and use food stocks on a rotating basis.

During hurricane season, monitor the tropics.

Monitor NOAA Weather Radio. It is an excellent / official source for real-time weather information and warnings

If a storm threatens, heed the advice from local authorities. Evacuate if ordered.

Execute your family plan

A HURRICANE WATCH issued for your part of the coast indicates the possibility that you could experience hurricane conditions within 36 hours. This watch should trigger your family's disaster plan, and protective measures should be initiated, especially those actions that require extra time such as securing a boat, leaving a barrier island, etc.

A HURRICANE WARNING issued for your part of the coast indicates that sustained winds of at least 74 mph are expected within 24 hours or less. Once this warning has been issued, your family should be in the process of completing protective actions and deciding the safest location to be during the storm.

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Hurricane Names

When the the winds from these storms reach 39 mph (34 kts), the cyclones are given names. Years ago, an international committee developed names for Atlantic cyclones (The History of Naming Hurricanes). In 1979 a six year rotating list of Atlantic storm names was adopted - alternating between male and female hurricane names. Storm names are used to facilitate geographic referencing, for warning services, for legal issues, and to reduce confusion when two or more tropical cyclones occur at the same time. Through a vote of the World Meteorological Organization Region IV Subcommittee, Atlantic cyclone names are retired usually when hurricanes result in substantial damage or death or for other special circumstances. The names assigned for the period between 2004 and 2009 are shown below.

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Saffir-Simpson Hurricane Scale

The Saffir-Simpson Hurricane Scale is a 1-5 rating based on the hurricane's present intensity. This is used to give an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall. Wind speed is the determining factor in the scale.

Tropical Storm
Winds 39-73 mph (34-63 kt)

Category 1 Hurricane
Winds 74-95 mph (64-82 kt)
No real damage to buildings. Damage to unanchored mobile homes.
Some damage to poorly constructed signs. Also, some coastal flooding and minor pier damage.
Examples: Irene 1999 and Allison 1995

Category 2 Hurricane
Winds 96-110 mph (83-95 kt)
Some damage to building roofs, doors and windows. Considerable damage to mobile homes. Flooding damages piers and small craft in unprotected moorings may break their moorings. Some trees blown down.
Examples: Bonnie 1998, Georges(FL & LA) 1998 and Gloria 1985

Category 3 Hurricane
Winds 111-130 mph (96-113 kt)
Some structural damage to small residences and utility buildings. Large trees blown down. Mobile homes and poorly built signs destroyed.
Flooding near the coast destroys smaller structures with larger structures damaged by floating debris. Terrain may be flooded well inland.
Examples: Keith 2000, Fran 1996, Opal 1995, Alicia 1983 and Betsy 1965

Category 4 Hurricane
Winds 131-155 mph (114-135 kt)
More extensive curtainwall failures with some complete roof structure failure on small residences. Major erosion of beach areas. Terrain may be flooded well inland.
Examples: Hugo 1989 and Donna 1960

Category 5 Hurricane
Winds 156 mph and up (135+ kt)
Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. Flooding causes major damage to lower floors of all structures near the shoreline. Massive evacuation of residential areas may be required.
Examples: Andrew(FL) 1992, Camille 1969 and Labor Day 1935.

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