Reported June 2005

Hurricanes can actually encourage the formation of tornadoes.

BACKGROUND: Scientists have discovered that hurricanes can actually encourage the formation of tornadoes. When meteorologists studied hurricane-related damage, they found some damage that didn't fit the pattern, and discovered it was actually damage resulting from hurricane-related tornadoes.

HOW TORNADOES FORM: Air is a gas and water is a liquid, but in the realm of science, both fall into the category of fluids. When a fluid's flow is disturbed somehow, it causes turbulence. For instance, branches sticking into and under the water can disrupt the flow of a stream, forming tiny eddies or whirlpools. The same thing happens when you move your hand quickly through water. Technically, these are known as vortices. The water moves in a circular motion around a central point, and this causes a depression or cavity to form in the center, which draws flowing objects towards that center. Think of water spinning down the bathroom drain.

These sorts of swirling vortices can also form in air. As a thunderstorm develops, if the wind speeds up and changes direction, this can cause a horizontal spinning effect in the lower atmosphere. As air rises, pulled upwards by the developing thunderstorm, it tilts the horizontal rotation into a vertical rotation. A tornado is simply a violently rotating column of air that extends from a thunderstorm in the atmosphere to the ground. The pressure inside can be 10-percent lower than the surrounding air, and this causes that air to rush towards the low-pressure center from all directions. As it streams inward, the air spirals upward around the core until it merges with the airflow of the thunderstorm that gave rise to the tornado.

TORNADO SAFETY TIPS:

Move to a pre-designated shelter, such as a basement

Stay away from windows

Get out of automobiles; don't try to outrun a tornado

Abandon your mobile home; they offer little protection from tornadoes.

An underpass is not safe: debris can fly underneath it and be deadly. Instead, head for a ditch.

The American Meteorological Society contributed to the information contained in the TV version of this report.

If you would like more information, please contact:

American Meteorological Society
45 Beacon Street
Boston, MA 02108-3693
(617) 227-2425

http://www.ametsoc.org