Beachgoers in Portugal Stunned After Spotting a 'Giant Wave' That Looked Like a Tsunami Approaching

Beachgoers in Portugal were stunned by a scene they witnessed near the sea on Sunday. The unique phenomenon unfolded on beaches such as Póvoa de Varzim, Vila do Conde, and Praia da Torreira in Aveiro, according to Portugal Pulse. According to the witnesses, mainly beachgoers, the scene seemed like a giant wave floating in the sky. The event shook the world when multiple videos and photos of the incident were shared on social media. Soon, experts and civilians started to discuss and debate the origin of the visual. However, scientists resolved the mystery and attributed the event to a rare atmospheric phenomenon known as "roll clouds."

'Roll Clouds'

The "roll clouds" started appearing on the beaches after a major heatwave swept the country on Sunday, June 29, 2025. Experts think that the visuals could be a consequence of the heatwave. The phenomenon was noticed in various parts of the country. On analysis, researchers immediately rejected the speculation that the event was associated with a tsunami. Instead, they claimed that the giant wave formed due to the existing contrast between air masses and sea breezes. Such a formation is called a roll cloud. 

The beachgoers claimed that the rolling clouds were accompanied by strong winds, according to The Portugal News. The Portuguese Institute for Sea and Atmosphere (IPMA) claimed that the clouds formed at sea around 3:30 pm. Thereafter, it travelled to the west coast of mainland Portugal between 5 pm and 6 pm. The organization has deemed the phenomenon to be "relatively rare." It was recognized in 2017 by the World Meteorological Organization's cloud atlas. 

This cloud is described as long and tubular in appearance by experts, according to Portugal Pulse. They move horizontally, which seems like the clouds are rolling over the ocean. Researchers believe that when warm air "clashes" with cold air, instead of rising, the interaction facilitates a horizontal expansion in the clouds, resulting in the spectacle.

Past Occurrences

Though experts attribute the phenomenon as rare, the event has been recorded in the past in Portugal. In 1999, "roll clouds" made an appearance in the Algarve. Back then, a panic situation developed due to the phenomenon. People believed that the "giant wave on the horizon" was an indicator of a tsunami, and fled the beach in hordes. Later investigation revealed that it was just an optical illusion caused by weather conditions. 

The phenomenon has mostly been associated with the southern part of the Gulf of Carpentaria in Northern Australia. It is the only place where such clouds can be predicted by experts. The estimate and observation are possible because of the unique arrangement exhibited by the territory and the sea. In Australia, these formations have been named the "morning glory cloud."

Ongoing Heatwave

The heatwave, which supposedly triggered the roll clouds, has taken over the country, per The Portugal News. It has already facilitated many forest fires. Other unstable meteorological phenomena possibly produced by the heatwave include hail, strong winds, heavy rains, and thunderstorms. The situation has become so serious that seven districts, such as Lisbon, Portalegre, Setúbal, Santarém, Évora, Beja, and Castelo Branco, have been placed on red alert.