Waterspout

Encyclopedia : W : WA : WAT : Waterspout

A waterspout near Florida.

A waterspout is an intense columnar vortex (usually appearing as a funnel-shaped cloud) that occurs over a body of water and is connected to a cumuliform cloud. In the common form, it is a nonsupercell tornado over water [link].

Types of waterspouts

Waterspouts, not associated with a rotating updraft of a supercell thunderstorm, are generally called "nontornadic waterspouts," or "fair-weather waterspouts,"http://www.galeschools.com/environment/glossary.htm#f while those associated with mesocyclones are called "tornadic waterspouts". Tornadic waterspouts are generally more intense than nonsupercell waterspouts, and really just resemble a tornado on water.

Fair weather waterspouts occur in coastal waters and are associated with usually weak, developing convective towers. They usually are F0, comprised of winds of less than 30 m/s. These are arguably the most common waterspouts in tropical climates, with upwards of 400 per year observed in the Florida Keys.National Weather Service Key West summary of waterspout types: http://www.srh.noaa.gov/eyw/HTML/spoutweb.htm They generally develop in warm weather with light surface winds, and form from the bottom-up.Ibid. Fair-weather waterspouts are similar to landspouts.

A pair of waterspouts off the Bahamas

Though the majority occur in the tropics, they can seasonally appear in temperate areas throughout the world, and are common across the western coast of Europe as well as the British Isles and several areas of the Mediterranean and Baltic Sea. They are not restricted to saltwater; many have been reported on lakes and rivers including all five Great Lakes. (4) They are more frequent within 100 kilometers (62 mi) from the coast than out in the open sea. Waterspouts are common along the southeast U.S. coast, especially off southern Florida and the Keys and can happen over seas, bays, and lakes worldwide. Approximately 160 waterspouts are currently reported per year across Europe, with the Netherlands reporting the most at 60, followed by Spain and Italy at 25, and the United Kingdom at 15.

Nautical threat

Waterspouts have long been serious marine hazards. Lucretius wrote about whirling columns that descended from the sky into the ocean and put sailors "into great peril"; history is filled with examples of ships being destroyed or damaged by them.

Stronger waterspouts are usually quite dangerous, posing threats to ships, planes, and swimmers. It is recommended to keep a considerable distance from either of these phenomena, and to always be on alert through weather reports. The U.S. National Weather Service will often issue special marine warnings when waterspouts are likely or have been sighted over coastal waters, or tornado warnings when waterspouts can move onshore.

References