How do waterspouts form and what risk do they pose?

The fatal sinking of a luxury yacht belonging to the British businessman Mike Lynch off the coast of Sicily has focused attention on the ocean phenomenon of waterspouts, how they are formed and the risk they pose to sailors in areas where they are more common.

What is a water spout?

According to the US National Ocean Service, waterspouts are a whirling column of air and water mist. They fall into two categories: fair-weather waterspouts and ones found during oceanic tornadoes that form during storms.

Related: UK tech entrepreneur Mike Lynch among missing in Sicily yacht sinking

Tornadic waterspouts, which develop downward in a thunderstorm, can either form over water or move from land to water and have the same characteristics as a land tornado. According to the NOS they are “often accompanied by high winds and seas, large hail, and frequent dangerous lightning”.

Fair-weather waterspouts, in contrast, usually form along the dark flat base of a line of developing cumulus clouds.

The waterspout that struck Lynch’s yacht appears to have been a tornadic waterspout, caused by one of the many storms that have swept through Italy in recent days, with floods and landslides causing severe damage in the north of the country after weeks of scorching heat.

Waterspouts are usually more common in tropical waters, but can appear anywhere, and those associated with severe storms can generate winds in excess of 100mph.

What is the danger of being hit by a water spout?

The energy from the winds in a waterspout can cause damage and injury, but the biggest risk involves a so-called knock-down which can tear off the mast.

While yachts are generally more difficult to capsize than smaller dinghies, a knock-down occurs when the yacht is struck by wind or waves with sufficient force to push the mast parallel with the water. The most serious scenario occurs when the mast drops below the water line.

Lynch’s yacht was fitted with a 75m mast, the world’s second tallest.

Is there any connection between water spouts and climate breakdown?

The growing intensity and frequency of severe weather events has been attributed to the climate crisis, although the link between tornadoes and the climate emergency is not fully understood.

According to the Royal Meteorological Society: “Rising global temperatures due to climate change means warmer air, which allows it to hold more moisture, roughly 7% more moisture per 1C of warming.

“This boosts the chance of thunderstorms, leading to more violent storms and more lightning strikes. And the intense downpours will lead to localised flash flooding.”

In one extraordinary incident last year 15 waterspouts were recorded in a single days by the International Centre for Waterspout Research off the coasts of Italy, France and Spain.