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Encyclopedic Entry

waterspout

waterspout

A waterspout is a column of rotating, cloud-filled wind. A waterspout descends from a cumulus cloud to an ocean or a lake.

Grades

4 - 12+

Subjects

Earth Science, Meteorology, Geography, Physical Geography

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A waterspout is a column of cloud-filled wind rotating over a body of water. 
 
Despite its name, a waterspout is not filled with water from the ocean or lake. A waterspout descends from a cumulus cloud. It does not "spout" from the water. The water inside a waterspout is formed by condensation in the cloud. 
 
There are two major types of waterspouts: tornadic waterspouts and fair-weather waterspouts.
 
Tornadic waterspouts get their start as true tornadoes. Influenced by winds associated with severe thunderstorms, air rises and rotates on a vertical axis. Tornadic waterspouts are the most powerful and destructive type of waterspout. 
 
Fair-weather waterspouts, however, are much more common. Fair-weather waterspouts are rarely dangerous. The clouds from which they descend are not fast-moving, so fair-weather waterspouts are often static. Fair-weather waterspouts are associated with developing storm systems, but not storms themselves.
 
Both tornadic and fair-weather waterspouts require high levels of humidity and a relatively warm water temperature compared to the overlying air. Waterspouts are most common in tropical and subtropical waters, such as the Florida Keys, the islands of Greece, and off the east coast of Australia.
 
There are five stages of waterspout formation:
 
1. Dark spot. The surface of the water takes on a dark appearance where the vortex, or column of rotating wind, reaches it.
 
2. Spiral pattern. Light and dark bands spiral out from the dark spot.
 
3. Spray ring. A swirling ring of sea spray called a cascade forms around the dark spot. It appears to have an eye at the center, similar to that seen in a hurricane.
 
4. Mature vortex. The waterspout is now at its most intense stage, visible from the surface of the water to the clouds overhead. It appears to have a hollow funnel and may be surrounded by vapor.
 
5. Decay. When the flow of warm air into the vortex weakens, the waterspout collapses.
 
The average spout is around 50 meters (165 feet) in diameter, with wind speeds of 80 kilometers per hour (50 miles per hour), corresponding to the weakest types of tornadoes on land. The largest waterspouts can have diameters of 100 meters (330 feet) and last for up to one hour, though the average lifetime is just 5 to 10 minutes. 
 
The National Weather Service recognizes the dangers posed by waterspouts as part of its "severe local storm" warning list. Waterspouts not only put swimmers and boaters at risk, they also pose a threat to aircraft. Helicopters flying near waterspouts can be damaged and thrown off-course by such intense winds.

Vocabulary

Term Part of Speech Definition

air

noun

layer of gases surrounding Earth.

axis

noun

an invisible line around which an object spins.

cloud

noun

visible mass of tiny water droplets or ice crystals in Earth's atmosphere.

condensation

noun

process by which water vapor becomes liquid.

correspond

verb

to match or be similar to.

cumulus

noun

type of large cloud with a flat bottom and fluffy tops.

decay

verb

to rot or decompose.

descend

verb

to go from a higher to a lower place.

diameter

noun

width of a circle.

endanger

verb

to put at risk.

eye

noun

center of a tropical cyclone, characterized by a roughly circular area of light winds and rain-free skies.

fair-weather waterspout

noun

column of rotating, cloud-filled wind that forms over water.

humidity

noun

amount of water vapor in the air.

hurricane

noun

tropical storm with wind speeds of at least 119 kilometers (74 miles) per hour. Hurricanes are the same thing as typhoons, but usually located in the Atlantic Ocean region.

lake

noun

body of water surrounded by land.

National Weather Service

noun

branch of the National Oceanic and Atmospheric Association (NOAA) whose mission is to provide "weather, hydrologic, and climate forecasts and warnings for the United States, its territories, adjacent waters and ocean areas, for the protection of life and property and the enhancement of the national economy."

ocean

noun

large body of salt water that covers most of the Earth.

storm

noun

severe weather indicating a disturbed state of the atmosphere resulting from uplifted air.

subtropical

adjective

bordering the tropics, just north of the Tropic of Cancer and south of the Tropic of Capricorn.

temperature

noun

degree of hotness or coldness measured by a thermometer with a numerical scale.

thunderstorm

noun

cloud that produces thunder and lightning, often accompanied by heavy rains.

tornadic waterspout

noun

column of rotating, cloud-filled wind that forms as a tornado moves over water.

tornado

noun

a violently rotating column of air that forms at the bottom of a cloud and touches the ground.

tropical

adjective

existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.

vapor

noun

visible liquid suspended in the air, such as fog.

vortex

noun

column of rotating fluid, such as air (wind) or water.

waterspout

noun

column of rotating cloud-filled wind that descends to an ocean or lake.

wind

noun

movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.

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