‘Felt like tsunami’: Rare ‘roll cloud’ stuns beachgoers in Portugal

Hundreds of beachgoers were left in awe on June 29 as a rare cloud formed at several beaches in Portugal, amid a record-breaking heatwave across the country.

People escaping the heat at beaches in the northern and central coast of Portugal were treated to an unusual tubular, wave-like “roll cloud” stretching across the shorelines, accompanied by heavy winds.

Social media was filled with photos and videos of the dramatic phenomena, which resembles a giant wave rolling across the sky.

It prompted some people to speculate if it is the onset of a tsunami.

“It was nuts to have experienced this rolling cloud in the north of Portugal,” a beachgoer with the handle Helder posted on X. “Felt like a tsunami out of a movie!”

Another X user with the handle Eagle Wings said: “This would have scared the daylights out of me.”

Roll clouds are a rare meteorological phenomenon formed from the interaction of air masses of contrasting temperatures and sea breezes.

Meteorologist and BBC weather presenter Sarah Keith-Lucas called it “a spectacular example of a roll cloud”.

“It’s a type of arcus cloud that can form near a powerful thunderstorm. Cool, moist air from over the ocean rolls in to meet warm, dry air over land. This rapid condensation, combined with air flowing in different directions above and below the cloud, shapes it into the distinctive cigar form, most commonly seen near coasts,” she told the broadcaster.

The phenomena comes as Portugal recorded its highest-ever single-day temperature in June – 46.4 deg C – on June 30 in Mora, some 100km east of the capital, Lisbon.

Portuguese weather agency IMPA said some 37 per cent of its monitoring stations recorded temperatures higher than 40 deg C on June 30.

The British Met Office said roll clouds – also known as arcus clouds – are low-level, wide ranging clouds that are typically associated with powerful storm clouds and thunderstorms.

The World Meteorological Organisation’s Cloud Atlas in 2024 officially named the roll cloud as a new type of cloud.

Roll clouds have been seen in other parts of the world, such as Australia, where cold air from Tasmania collides with hot air on the mainland.