A superyacht carrying 22 people, including British tech entrepreneur Mike Lynch, sank off the coast of Palermo, Italy, in the early hours of August 19.
The 183-foot Bayesian yacht is believed to have been hit by a waterspout—a tornado that forms over the ocean—and some experts are concerned that climate change could worsen these storms in the Mediterranean and other quickly warming waters.
Here’s what you need to know about waterspouts and whether hotter temperatures could cause more of them.
What is a waterspout?
A waterspout is a tornado that forms over water. “The tornado doesn't really care what surface it’s over,” says David Sills, executive director of the Northern Tornadoes Project at Western University in Ontario, Canada. “Whether it's a city or a forest or crops or water, the tornado is going to do its thing."
These columns of rotating air “form where an air boundary exists, for example where warm and cold air collide,” says a spokesperson at the Australian Government Bureau of Meteorology (BOM) via email.
Changes in wind direction at different heights can cause a rotation.
“Imagine just above the ocean, the wind is blowing in one direction,” says Peter Inness, meteorologist at the University of Reading. When the wind higher up blows in another direction, “the air between those two levels of wind starts rotating around the horizontal axis.”
The warm air below rises and these “spinning parcels of air are also lifted and stretched in this process and can concentrate on the surface of the water creating a vortex,” says the BOM.
As the air is sucked upwards into the storm, the spinning intensifies like taking the plug out of the bath, says Innes: “the water going down the plughole rotates very intensely because it's being sucked downwards.”
It’s similar to a figure skater, adds Sills: “When they bring in their arms, and then they spin faster and faster.”
How dangerous are waterspouts for boats?
Although the wind associated with waterspouts can reach 55 miles per hour, they typically move at under 25 miles per hour, are short-lived, and don’t cause much damage. “They usually only impact any single point for a few minutes,” says the BOM.
The Bayesian was moored overnight when it sank. Although people have attributed this to a waterspout, it’s not yet been confirmed.
“It was dark and there are no images available,” says Luca Mercalli, president of the Italian Meteorological Society, via email.
Boats are designed to right themselves when blown over by strong winds. “Those sailboats have a big, heavy keel so that when you start to go over, it pulls you back up,” says Sills.
But if water gets into the ship, it can lose buoyancy. “It's called a knockdown,” he says. “Time spent over like that means water and waves can get into open doors and it starts to take on water. Then you start to sink.”
The rapid change in wind strength and direction are also dangerous for boats, says Innes, “because it could result in the boat rocking backward and forward very violently.”
Will climate change cause more waterspouts?
One study has found more frequent waterspouts off the coast of Spain’s Balearic Islands when sea surface temperatures are higher, particularly between 73 and 78°F.
This year, “the Mediterranean is [over 5°F] above average,” says Mercalli, which is “an anomaly considered "extreme". These unusually warm waters could be partly due to climate change as well as year-on-year variability.
Some people are concerned that climate change could cause an increase in tornadoes on land and water.
“Global warming will increase all weather extreme events, because it injects more energy into the atmosphere,” says Mercalli.
But experts are wary of confirming a definite link with climate change. “Waterspouts are a very short-lived and local scale phenomena, and therefore difficult to attribute to impacts of climate change,” says the BOM.
The Mediterranean is warming more quickly than the rest of the ocean. Although climate change will make sea surface temperatures warmer, it’s unclear how it will affect the other conditions needed to create waterspouts.
Waterspouts need a temperature difference between air and sea. If the air is warming at the same rate as the bodies of water, an increase in waterspouts is unlikely, says Sills.
Low pressure is also needed. “Even if the water is really warm, if you've got an area of high pressure over the Mediterranean, you won't get those thunderstorms,” says Inness. “You won't get waterspouts.”
Wind direction also comes into play. In this region, humid air from the north is more likely to cause storms than dry winds coming up from North Africa.
Due to poor historic data, it’s not possible to confirm that waterspouts are increasing, says Mercalli, “but surely all heavy storms, including thunderstorms that generate strong winds, downbursts, heavy rains and hail are increasing worldwide and in Italy.”
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