|Spaulding, Nancy E. and Samuel N. Namowitz. Heath Earth Science.Lexington, MA: Health, 1994: 559.||"The strongest winds in a tornado are between 360 and 500 kilometers an hour."||100–140 m/s|
|World Book Encyclopedia. New York: World Book, 1998: 333-5.||"Tornado winds swirl at speeds that way exceed 300 miles per hour."||130 m/s|
|Allaby, Michael. Dangerous Weather: Tornadoes. New York: Facts on File. 1997: 97-101.||"Some generate winds at only 60 mph or even less, others of 300 mph or more…."||27–130 m/s|
|Robinson, Andrew. Earth Shock: Hurricanes, Volcanoes, Earthquakes, Tornadoes and Other Forces of Nature. London: Thames & Hudson. 1993: 136.||"Tornadoes combine terrifyingly powerful wind speeds -- 300–350 mph, maybe even 550 mph…."||130–160 m/s
|Introduction to Tornadoes. Severe Weather Institute Research Lab. Warner Bros. Movies.||"Experts once thought tornado winds exceeded 500 mph. Research in recent years, however, has shown that winds rarely exceed 250 mph and most tornadoes have winds of less than 112 mph."||50–110 m/s|
The word tornado came from the Spanish word "tronada" which means a thunderstorm. A tornado, also known as a twister, is a violent spiral-shaped storm with a rapidly rotating column of air rising upward forming a vortex. The vortex has relatively low pressure at the center and is shaped like a funnel. Tornadoes that occur over oceans are called waterspouts, they are usually weaker than tornadoes.
The condition for a severe thunderstorm and for a tornado are basically same. Most violent tornadoes are formed from powerful thunderstorms known as supercells. Some sign of a coming tornado are a light rain, then heavier rain and rain mixed with hail. Tornadoes usually occur during the spring and early summer.
Tornadoes usually lasts only a few minutes, but they are very intense. Their wind speeds range from 18 to 140 m/s. The damage path of a tornado is usually less than 500 meters wide and it travels at less than 16 m/s. Each year, the United States ranks number one in tornado incidence with Australia coming in second. Very often, the most devastating ones occur in Bangladesh.
The damage from a tornado is determined by the speed of its winds. Tetsuya Theodore Fujita, a weather scientist, developed a scale known as the Fujita Tornado Intensity Scale to determine the damage based on wind speed (see table below).
|F-0||18-32||Light -- tree branches broken, damage to chimneys and large signs.|
|F-1||33-50||Moderate -- trees snapped, surface of roofs peeled off, windows broken.|
|F-2||51-70||Considerable -- large trees uprooted, roofs torn off frame houses, mobile homes demolished.|
|F-3||71-92||Severe -- roof and some walls torn off well-constructed houses, cars overturned.|
|F-4||93-116||Devastating -- well-constructed houses leveled, cars and large objects thrown.|
|F-5||117-142||Incredible -- strong frame houses lifted off foundation and destroyed, cars-sized objects thrown more than 90 meters.|
Shamim Rizvi -- 1999