Stay Signed In
Do you want to access your site more quickly on this computer? Check this box, and your username and password will be remembered for two weeks. Click logout to turn this off.
Stay Safe
Do not check this box if you are using a public computer. You don't want anyone seeing your personal info or messing with your site.
Most people associate twisters with tornadoes, but in fact tropical twisters come from hurricanes. Hurricanes are what scientists call "strong Tropical Cyclones". They are formed when large areas of the ocean become heated, and the air pressure over that area drops. This causes thunderstorms and strong surface winds. Cyclones develop over tropical or sub-tropical waters (for example, in the Atlantic off the coast of Africa, or in the Pacific). As they travel long distances gathering energy from the ocean, they are likely to be classified as strong Tropical Cyclones. When the winds of a tropical storm reach 74 mph, then the storm is classified as a hurricane.
A tropical cyclone is a meteorological term for a storm system characterized by a low pressure system center and thunderstorms that produces strong wind and flooding rain. A tropical cyclone feeds on the heat released when moist air rises and the water vapor it contains condenses. They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easters, European windstorms, and polar lows, leading to their classification as "warm core" storm systems.
Weak Tornadoes
69% of all tornadoes
Less than 5% of tornado deaths
Lifetime 1-10+ minutes
Winds less than 110 mph
Strong Tornadoes
29% of all tornadoes
Nearly 30% of all tornado deaths
May last 20 minutes or longer
Winds 110-205 mph
Violent Tornadoes
Only 2% of all tornadoes
70% of all tornado deaths
Lifetime can exceed 1 hour
Lifetime can exceed 1 hour
How is a tornadoe formed?
Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere.
<>
Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical.
<>
An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.
