Hurricane Awareness: Winds and Tornadoes

July 18, 2012

Both hurricanes and tropical storms produce dangerous winds that can produce life-threatening conditions to those who are caught in them. Hurricane-force winds can easily destroy poorly constructed buildings and mobile homes. Debris such as signs, roofing material, and small items left outside can become flying missiles in hurricanes. Extensive damage caused by falling trees can lead to lengthy power and phone outages.

Tropical circulations are classified based on the following wind speed criteria:
Wind Speed	Name
less than 39 mph	Tropical Depression
39 to 73 mph	Tropical Storm
74 mph or greater	Hurricane

Hurricanes are further divided into 5 categories based on the destructive power of their winds. The scale used in hurricane classification is called the Saffir-Simpson scale. Below is a list of the Saffir-Simpson scale, the typical damage that occurs with storms of each category, and examples of each category of storm (at landfall).

Saffir-Simpson Hurricane Scale
Category	Definition/Effects
1	Winds: 74-95 mph (64-82 kt) No real damage to well-constructed buildings. Damage primarily to poorly constructed buildings and unanchored mobile homes, shrubbery, and trees. Also, some coastal flooding and minor pier damage is possible. Examples: Irene 1999 and Allison 1995.
2	Winds: 96-110 mph (83-95 kt) Some damage to building roofs, doors, and windows. Considerable damage to vegetation, mobile homes, etc. Flooding damages piers and small craft in unprotected moorings may break their moorings. Examples: Bonnie 1998, Georges (FL & LA) 1998 and Gloria 1985.
3	Winds: 111-129 mph (96-112 kt) 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 may be flooded well inland. Examples: Katrina 2005, Fran 1996, Opal 1995, Alicia 1983 and Betsy 1965
4	Winds: 130-156 mph (113-136 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
5	Winds: 157+ mph (137+ 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(Florida) 1992, Camille 1969 and Labor Day-Florida Keys 1935

Hurricanes can also produce tornadoes that add to the storm's destructive power. Tornadoes are most likely to occur to the right side of the hurricane track. However, they can also form in the rain bands, well away from the center of the hurricane. Studies have shown that more than half of land-falling hurricanes produce at least one tornado.

In general though, tornadoes associated with hurricanes are less intense than those that occur in the Great Plains. Nonetheless, the effects of tornadoes, added to the larger area of hurricane-force winds, can produce substantial damage. Fortunately, hurricane-spawned tornadoes are infrequent in Northern New England.

Fact for the Day: It makes a difference which side of the hurricane you are on.

Question of the Day: How often do we get hurricanes of each category in Maine? Find out the answer

The National Weather Service has declared the week of July 16th through the 20th to be Hurricane Awareness Week in New England. (This information was prepared by the National Weather Service, Gray, Maine.

For additional information about hurricanes and hurricane safety, visit the National Hurricane Center's web site

Also visit National Weather Service Caribou and Gray

MAINE EMERGENCY MANAGEMENT AGENCY

Hurricane Awareness: Winds and Tornadoes

July 18, 2012

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