Watch Out for Waterspouts

31 August 2009 By David Cannon, Weather Routing Inc.

Mariners know (or at least they should know) that waterspouts are not just fascinating phenomena but also dangers to be avoided at all costs. But what exactly is a waterspout? Is it simply a tornado over the water, or is it something more?

Like tornadoes, waterspouts are intense vortices that appear as funnel-shaped clouds. Unlike tornadoes, which typically descend from their parent cloud mass, however, waterspouts tend to develop on the sea’s surface and move skyward, drawing water up along with them. While they are usually weaker than their land-based counterparts (tornadoes), stronger waterspouts can form from smaller-scale (or mesoscale) cyclones. Most waterspouts form in an even smaller scale (microscale) environment that is typically no more than one to two kilometers in total area.

Waterspouts are most commonly found in tropical climates, though in rare instances they can form in northern, more temperate climates. They frequently are found in the lee of land masses (off the Florida coast and across the Florida Keys, for example). Generally speaking, waterspouts will most likely form late in the afternoon or early in the evening, following the period of maximum temperature lapse rate from the ocean surface skyward.

Waterspouts typically go through a five-stage life cycle.

  1. First, you will see a dark spot form over the water;
  2. Following that is the formation of light and dark bands “spiraling out” from the dark spot;
  3. Next, a dense, swirling ring of sea spray forms around the dark spot;
  4. Then the waterspout becomes visible from the sea surface to the cloud mass overhead, and reaches its maximum intensity (its “mature” phase);
  5. Finally, the waterspout begins its decay phase, leading to its eventual dissipation.

Typically, the entire life cycle of a waterspout is no more than 15 to 20 minutes in duration.

Don’t make the mistake of driving over to get a better look at a waterspout you spot in the distance. While waterspouts tend to be smaller and weaker than tornadoes, make no mistake about it, they are potentially lethal. They may be brief phenomena, but waterspouts have been known to bring life-threatening winds as high as hurricane-force.

As recently as June, 26, 2009, a waterspout moved up the St. Johns River into downtown Jacksonville, Florida, where it was seen by hundreds of people on their way home in rush-hour traffic. In addition to creating a boating hazard on the river, when the waterspout touched ashore, it caused major flooding, brought down power lines and knocked out power to thousands of homes.

You can stay abreast of waterspouts forming in a particular area through online weather websites. Various government agencies, such as the U.S. National Weather Service, provide warnings and advisories on waterspouts as they form or are spotted by weather observers in the general area. Private weather companies and weather consulting firms also keep mariners informed of the potential for waterspouts in their cruising area by checking local radar trends, as squall areas move through a particular region.

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