Beachgoers in Portugal scrambled for cover over the weekend as the sweltering heat gave birth to a rare “tsunami roll,” or ominous wave of dark clouds over the water.
Viral video of Sunday’s phenomenon showed bathers in Praia de Buarcos in awe of the enormous roll cloud approaching the beach as it began blocking out the sun and kicking up gusts of winds.
“It was nuts to have experienced this rolling cloud in the north of Portugal,” a beachgoer wrote on X. “Felt like a tsunami out of a movie!”
While the tubular, wave-like clouds brought some panic to the beach, as people feared it was a sign of a coming tsunami, the visual marvel was actually just part of a natural phenomenon known as an arcus cloud, or roll cloud.
The “relatively rare” clouds are formed by low-level, wide-ranging clouds that are typically associated with looming thunderstorms, according to the National Weather Service.
The ominous clouds are typically formed when a thunderstorm front pushes out cooler air, causing the warm, humid air to condense into a cloud that can get “trapped” and start to spin horizontally.
The Portuguese beach was primed to experience the phenomenon after its temperatures hit more than 107 degrees Sunday, with heavy rain, thunderstorms and even hail following the roll cloud.
The roll cloud allegedly stretched more than 90 miles along Portugal’s coast, with sightings reported from Vila do Conde to Figueira da Foz, according to local outlets.
