Tornadoes are one of nature's most violent storms. In an average year, about 1,000 tornadoes are reported across the United States, resulting in 80 deaths and over 1,500 injuries. A tornado is a violently rotating column of air extending from a thunderstorm to the ground. The most violent tornadoes are capable of tremendous destruction with wind speeds of 250 mph or more. Damage paths can be in excess of one mile wide and 50 miles long. 

Tornado'es come in all shapes and sizes and can occur anywhere in the U.S. at any time of the year. In the southern states, peak tornado season is March through May, while peak months in the northern states are during the summer.

The Tampa-area historical tornado activity is above Florida state average, and is 114% greater than the overall U.S. average.

On 4/4/1966, a category 4 (max. wind speeds 207-260 mph) tornado 23.3 miles away from the Tampa city center killed 11 people and injured 530 people and caused between $5,000,000 and $50,000,000 in damages. On 4/15/1958, a category 4 tornado 23.4 miles away from the city center injured 7 people and caused between $5000 and $50,000 in damages.

For more information:
Florida Tornado information
NOAA