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.
waterspout
Waterspouts are common in warm, humid areas, such as the Bahamas, above.

Landspout
A landspout, officially called a "dust-tube tornado," is similar to a waterspout. Unlike a true tornado, landspouts do not form from a mature mesocyclone. Like a waterspout, a landspout forms with a slow-moving (nor not-moving), developing cloud system.

Snowspout
In January 1994, a waterspout near Whitby, Canada, off the shore of Lake Ontario, provided a rare example of a snowspout—a waterspout in winter conditions. The air moving over the water to produce snowspouts can be so cold that steam rises from the surface.

Noun

layer of gases surrounding Earth.

Noun

an invisible line around which an object spins.

Noun

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

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.

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.

Noun

body of water surrounded by land.

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."

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.

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.

Noun

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

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.