On the afternoon of Sunday, 29th June, various towns on the northern coast of Portugal, such as Póvoa de Varzim, Figueira da Foz, Vila do Conde, Peniche, Nazaré, and Esposende, were the scene of an unusual meteorological phenomenon that created a striking visual impact: a tubular cloud advanced horizontally over the sea towards the coast, resembling a giant wave.
The formation, documented by bathers and surfers through videos and photos shared on social media, was not related to any extreme phenomenon and posed no risk to the public. Despite its appearance, it was neither a tsunami nor a storm, but a cloud volutus, also known as a “rolled cloud”.
According to the Portuguese Institute of Sea and Atmosphere (IPMA), these clouds are characterised by their tubular structure and move around a horizontal axis. They form in situations of strong thermal contrast between warm air coming from the land and cooler sea breezes. Instead of rising, the warm air expands laterally upon encountering the cold air, creating a dense and elongated condensation that results in this distinctive cloud.
The phenomenon began to form offshore around 15:30 and approached the land between 17:00 and 18:00, accompanied by a drop in temperature — in some areas by up to eight degrees in an hour — and a sudden increase in wind speed, which led many people to temporarily leave the beaches.
🇵🇹 | A cloud tsunami sweeps across three Portuguese cities.
An unusual atmospheric phenomenon struck Portugal: a gigantic spiral cloud resembling a tsunami was detected in three coastal cities.
These clouds form due to sea breezes and appear as a mass… pic.twitter.com/Pd212wg8qy
— Alerta News 24 (@AlertaNews24) 30th June 2025
The World Meteorological Organization (WMO) officially included this type of cloud in its atlas in 2017, under the genus volutus, which may be associated with altocumulus or stratocumulus. Satellite images from the third generation Meteosat system documented its evolution, linked to internal gravity waves in the lower layers of the atmosphere.
Although infrequent in Portugal, this type of formation is well known to meteorologists and weather watchers, typically developing in contexts of heatwaves or sudden changes in air masses. On this occasion, its appearance coincided with high temperatures in the region and mostly clear skies.
