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Waterspout: A Tornado's Close Cousin

UPDATED March 18, 2009

By WeatherBug Meteorologist, Angela Johnson

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If you have seen "The Wizard of Oz" or "Twister" then you are familiar with tornadoes. However, did you know that tornadoes have a close cousin, the waterspout?

A waterspout, like a tornado, is a rotating column of air that occurs over a body of water. There are two types of waterspouts: Non-tornadic and tornadic.

Non-tornadic waterspouts, also known as fair-weather waterspouts, develop on the surface of the water and then work their way up to the cloud.

Fair-weather spouts form in light - - or generally "fair" - - wind conditions and move slowly, if at all. They seldom make their way far inland and when they do they dissipate rapidly. If a fair-weather waterspout does move on land, it then becomes a tornado and the National Weather Service (NWS) will issue a tornado warning.

Fair weather waterspouts are common over South Florida`s coastal waters from late spring to early fall. They also occur in the Great Lakes during August, September, and October, when the water is at its warmest.

Fair weather waterspouts form in the Great Lakes area when cold air moves over the water which leads to a large temperature difference between the warm water and the cold air.

Tornadic waterspouts are also referred to as a tornado over water and develop downward. These form like a regular tornado; just over water. They can also be a tornado that moves from land to water. Just like land tornadoes, these waterspout are associated with severe thunderstorms and produce high winds and seas, large hail and dangerous lightning.

Both types of waterspouts can produce a sharp increase in wind speed and can cause damage to a boat. If the waterspout goes on land it can cause damage to structures and possibly cause injury or death, depending on its strength.

When a waterspout has been detected on radar or one has been spotted the NWS issues a Special Marine Warning.

Some waterspout safety from the NWS:

  • Listen for special marine warnings about waterspout sightings that are broadcasted on NOAA Weather Radio.
  • Watch the sky for certain types of clouds. In the summer, with light winds, look for a possible waterspout underneath a line of cumulus clouds with dark, flat bases. Anytime of year, a thunderstorm or line of thunderstorms can produce very intense waterspouts.
  • If a waterspout is sighted, immediately move away at a 90-degree or right angle from the apparent motion of the waterspout.
  • Never try to navigate through a waterspout. Although waterspouts are usually weaker than tornadoes, they can still damage your boat and endanger you.

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