III - TORNADOES

DEFRAYING THE ECONOMIC COSTS OF DISASTERS

TORNADOES

A tornado is a violently rotating column of air that extends from a thunderstorm and comes into contact with the ground, according to the National Oceanic and Atmospheric Administration (NOAA). In an average year about 1,000 tornadoes are reported nationwide, according to NOAA. Tornado intensity is measured by the Fujita (F) scale. The scale rates tornadoes on a scale of 0 through 5, based on the amount and type of wind damage. It incorporates 28 different “damage indicators” based on damage to a wide variety of structures ranging from trees to shopping malls.

THE FUJITA SCALE FOR TORNADOES

		Original F scale (1)	Enhanced F scale (2)
Category	Damage	Wind speed (mph)	3-second gust (mph)
F-0	Light	40-72	65-85
F-1	Moderate	73-112	86-110
F-2	Considerable	113-157	111-135
F-3	Severe	158-207	136-165
F-4	Devastating	208-260	166-200
F-5	Incredible	261-318	Over 200
(1) Original scale: wind speeds represent fastest estimated speeds over ¼ mile. (2) Enhanced scale: wind speeds represent maximum 3-second gusts. Source: U.S. Department of Commerce, National Oceanic and Atmospheric Administration.

Although tornadoes can occur at any time of the year, the weather conditions that cause tornadoes are common in the southern states in March through May. Peak months in the northern states are during the summer.

NUMBER OF TORNADOES AND RELATED DEATHS PER MONTH, 2007 (1)

(1) Data not yet final.

Source: U.S. Department of Commerce, Storm Prediction Center, National Weather Service.

TORNADOES AND RELATED DEATHS IN THE UNITED STATES, 1987-2007 (1)

Year	Tornadoes	Deaths	Year	Tornadoes	Deaths	Year	Tornadoes	Deaths
1987	656	59	1994	1,082	69	2001	1,216	40
1988	702	32	1995	1,234	30	2002	941	55
1989	856	50	1996	1,173	25	2003	1,376	54
1990	1,133	53	1997	1,148	67	2004	1,819	36
1991	1,132	39	1998	1,424	130	2005	1,264	38
1992	1,297	39	1999	1,345	94	2006	1,106	67
1993	1,173	33	2000	1,071	40	2007	1,093	81
(1) Excludes Puerto Rico. Does not include tornadoes crossing state lines. Counts these tornadoes as one event. Source: U.S. Department of Commerce, Storm Prediction Center, National Weather Service.