Dr Pieter Groenemeijer, director of the European Severe Storms Laboratory, added that while waterspouts are common across the Mediterranean, including Italy, they are rarely lethal.
Extreme weather killed 534 people in Europe last year, he said, with just three of them being caused by tornadoes or waterspouts.
“Some thunderstorms managed to form overnight in the neighbourhood of a larger cyclone located a little bit further north over the Ionian sea,” Dr Groenemeijer said.
“We saw a very active storm moving towards the coast during the night with a lot of lightning activity and it seems that either a waterspout or a very strong downburst was enough to capsize the boat.
“A waterspout would really only affect you maybe tens of metres from the centre of the waterspout.
“If this storm had happened in just a slightly different location, or the yacht were anchored somewhere a little bit further away, then this probably wouldn’t have happened.”
Eyewitnesses on the ground claim they saw a waterspout form and neighbouring boats were left unsunk by the storm.