Sicily yacht sinking: What is a waterspout and how dangerous can it be?

File photo: People watch on as a waterspout forms over the St Johns River in Jacksonville, Florida, in 2009.
People watch on as a waterspout forms over the St Johns River in Jacksonville, Florida, in 2009. Credit: AP

A weather phenomenon known as a waterspout is believed to be what caused a superyacht to sink off the coast of Sicily earlier this week.

Six people, including a British technology tycoon, remain missing after the vessel, named Bayesian, sank on Monday.

The sinking appeared to catch the vessel's crew by surprise, with its captain telling Italian media: "We didn't see it coming."

Eyewitnesses have described the frightening speed at which the yacht appeared to sink as it was battered by an apparent waterspout. But what exactly is one? ITV News explains.

What is a waterspout?

A waterspout is defined as a whirling column of air and water mist, according to the US National Ocean Service.

It can appear similar to a land tornado and is generally broken down into two categories: fair weather and tornadic.

The latter are tornadoes that form over water, or move from land to water. Generally, these are associated with severe thunderstorms and accompanied by other types of weather, including high winds and lightning.

Comparatively, fair weather waterspouts are not associated with thunderstorms, and tend to develop along the base line of developing cumulus clouds.

A fair weather waterspout will develop on the water's surface and work upwards as it grows. Tornadic waterspouts, meanwhile, will develop downward in a thunderstorm.

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Waterspouts are whirling columns of air and water mist. Credit: AP

How dangerous are waterspouts?

Tornadic waterspouts are the most powerful and destructive type of waterspout, National Geographic reports, and can pose a threat to life.

In comparison, fair weather waterspouts - which occur more often than tornadic - are rarely dangerous due to their static nature.

Where do waterspouts form?

Generally, waterspouts are most common in tropical and subtropical waters, including the Florida Keys and the east coast of Australia.

Both types of waterspouts require high levels of humidity and a relatively warm temperature compared to the overlying air in order to develop properly.

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