A roll cloud suddenly hit the coast of Hendaye, in the Pyrénées-Atlantiques department of northern France, causing beachgoers to flee. A roll cloud is a cloud formation shaped like a long cylinder of water vapor that moves rapidly and can extend for tens of kilometers. The phenomenon brought wind gusts of up to 70 km/h, lifting large amounts of sand and sweeping away umbrellas and towels. Temperatures dropped by about 10 degrees within minutes. Swimmers, caught by surprise, quickly left the beach.