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4 . 1 . 3 Tornadoes <br /> 4. 1 . 3. 1 Hazard Identification <br /> A tornado is a violent windstorm characterized by a twisting , funnel shaped cloud <br /> extending to the ground . It is generated by a thunderstorm or hurricane when cool air <br /> overrides a layer of warm air, forcing the warm air to rise rapidly . The most common type of <br /> tornado , the relatively weak and short-lived type , occurs in the warm season , with June being <br /> the peak month . The strongest, most deadly tornadoes occur in the cool season , from <br /> December through April ( FDCA, 2004b ) . Occasional windstorms accompanied by tornadoes , <br /> such as the winter storm of 1993 , also are widespread and destructive . <br /> When a tornado threatens , only a short amount of time is available for <br /> life-or-death decisions . The NWS issues two types of alerts : <br /> Tornado Watch — means that conditions are favorable for tornadoes to <br /> develop . <br /> • Tornado Warning — means that a tornado has actually been sic hted . <br /> Tornadoes are classified using the Fujita- Pearson scale (Table 4 . 16 ) . <br /> Table 4 . 16 . Fujita- Pearson Scale . <br /> F = Intensity P = Path Length W = Mean Width <br /> FO = Light Damage PO = less than 1 mile WO = less than 0 . 01 mile <br /> F1 = Moderate Damage P1 = 1 . 0 to 3 . 1 miles W1 = 0 . 01 to 0 . 03 miles <br /> F2 = Considerable Damage P2 = 3 . 2 to 9 . 9 miles W2 = 0 . 04 to C , 09 miles <br /> F3 = Severe Damage P3 = 10 . 0 to 31 . 0 miles W3 = 0 . 10 to C . 31 miles <br /> F4 = Devastating Damage P4 = 32 . 0 to 99 . 0 miles W4 = 0 . 32 to C , 99 miles <br /> F5 = Catastrophic Damage P5 = 100 miles or greater W5 = 1 . 00 miles or wider <br /> Historic Events. Florida ranks third in the United States in the number of tornado <br /> strikes , and the first in the number of tornadoes per square mile . The odds of a tornado <br /> striking any specific point in southeastern Florida are 0 . 04 , or once per 250 years . <br /> The damage from a tornado is a result of the high wind velocity and wind - blown <br /> debris . Florida ' s average is 75 tornadoes annually since 1950 , causing an average of <br /> 3 fatalities and 60 injuries each year ( FDCA, 2004b ) . According to FDCA on- line hazard <br /> maps , there have been three light damage , one moderate damage , and two significant <br /> damage tornadoes in Indian River County between 1961 and 1990 . Table 4. 17 illustrates the <br /> associated wind speeds with each of the tornado damage categories used in the FDCA map . <br /> `hr�r <br /> 4-29 <br />