A boat packed full of British tourists capsized during a catastrophic storm over Italy's Lake Maggiore yesterday.
Local reports say the vessel, believed to be a houseboat, capsized after a "whirlwind" struck the lake - a popular destination for British holidaymakers on Italy's border with Switzerland.
According to weather data from the day of the sinking, massive thunderstorms were seen surrounding the huge 212 sq km (132 sq miles) lake in northern Italy.
Officials initially blamed the disaster on a weather phenomenon known as a whirlwind - a rotating column of air created by turbulence that creates a vertical vortex billowing into the sky.
They can strike in any part of the world and at any time of year.
Tornadoes fall into the whirlwind category, as do water and landspouts. These are known as great, or "major", whirlwinds.
The tornado is formed when a number of hypercharged thunderstorms, known as a supercell, club together and their storms begin to spin. As the air is circulated, a cloud forms around the high-altitude wind - making it visible.
However, there are also a number of smaller scale whirlwinds which can effect smaller areas. Some examples of these are the gustnado, fire whirl, dust devils and steam devils.
Earlier this year, a dust devil struck British shores as one touched down on the sands of north Wales during Storm Franklin, which was accompanied with torrential rain and flooding across the country.
The key difference between the two is that the minor whirlwind is formed when local winds spin on the ground, causing a funnel to form. It is visible because of the debris it picks up from the ground.
It's unknown which type of whirlwind struck the boat that capsized in northern Italy this weekend.
Overnight, search and rescue divers trawled the lake floor to find the bodies of two passengers who couldn't be found after the boat sank.
The last of the two bodies was retrieved from the lake in the early hours of Monday morning.
Twenty-five people were on board at the time, and the majority of them managed to swim to the safety of the lakeside towns of Lisanza and Piccaluga.
Some of the survivors were picked up by other boats. A total of 19 people were saved.
Firefighter video released Sunday showed pieces of wood floating in the lake as a helicopter flew overhead.
The whirlwind was part of a storm system that hit Lombardy Sunday evening, forcing delays at Milan's Malpensa airport.
