Waterspouts are generally a weaker cousin to tornadoes. By definition, a waterspout is a tornado over water but there's a little more to it than that.
A waterspout can form from either an ordinary cumulus cloud or it can form from a thunderstorm. Also by definition, when a waterspout moves from water onto land, then it is called a tornado. While weak waterspouts that move onshore will result in a tornado warning, they typically don't last very long and do little serious damage. The most common type of waterspout along the central Gulf Coast comes from fair-weather cumulus clouds and is too low in the sky and too weak to be detected by radar.
Tornadoes form from severe thunderstorms that are driven by the wind shear, rotation and rising motion within the storm cell. Waterspouts that form this way really are tornadoes that just happen to be over water. Similarly, a tornado that crosses a lake really is still a tornado.
Waterspouts are found over lakes and oceans all around the world. In the fall they can form around the Great Lakes and in other colder climates where lakes are still warm. In 2003, there was a record outbreak of waterspouts on the Great Lakes.
Waterspouts don't need a powerful storm to create them. They seem to thrive on the warm, moist air above water, especially when there is little wind shear, and when air above the clouds is cooler than average, particularly in northern climates. Similar to a tornado, a waterspout that is starting or ending is simply called a funnel cloud if it is not contacting the water. Like other weather phenomena, waterspout reports should be expected to rise simply due to the increasing number of people on the coasts and the increasing number of smart phone cameras that can capture them.
This video from NOAA gives a good description of what we know about waterspouts.
Here are some waterspout safety tips from the Jacksonville office of the National Weather Service.
-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 the year, a thunderstorm or line of thunderstorms, can produce very intense waterspouts.
-If a waterspout is sighted, immediately head at a 90 degree angle form the apparent motion of the waterspout. Never try to navigate through a waterspout. Although waterspouts are usually weaker than tornadoes, they can still produce significant damage to you and your boat.
NASA is just one agency that is trying to better understand waterspouts.
Typical Gulf Coast waterspouts on quiet weather days seem to linked to the land breeze that moves offshore at night and then returns inland in the days as a sea breeze. In the Florida Keys, waterspouts have produced winds estimated at over 100mph. There's a wide range of weak to strong waterspouts and there's a still a long way to go in understanding how and when they form. The difficulty also is that there is not always a clear line between the structure of a strong waterspout and a weak tornado. There's actually an organization dedicated to logging waterspout reports to help scientists better-understand them. It's called the International Centre for Waterspout Research. Check out their photo gallery to see the wide variety of shapes of waterspouts.
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