A tornado is a violent whirling wind, characteristically accompanied by a funnel-shaped cloud extending down from a cumulonimbus cloud. The air pressure at the bottom of the funnel of swirling air is extremely low. When this low pressure area touches the ground, it acts like a giant vacuum cleaner.
Some tornadoes even occur over water.
A tornado over a lake or ocean is called a waterspout. Tornadoes generally exhibit a certain characteristic cycle of behavior between formation and final disappearance. The first sign of a tornado may be a strong whirlwind of dust from the ground surface, often at the same time as a short funnel grows from the storm cloud above it. The funnel then becomes more organized and descends further from the cloud, sometimes touching the ground. Meteorologists are not sure how tornadoes form.