Southern Europe was recently hit with an intense heawave, with temperatures in Spain, Portugal, Greece, and France reaching over 40C, causing extreme heat, wildfire, and health warnings.
However, beachgoers in northern Portugal rushed to leave to find shelter after they saw a rare ‘tsunami roll’, a wave of dark clouds, appeared in the sky over the water – another reaction of the extreme temperatures the country had experienced.
The cloud appeared like a wave crashing in the sky, with beachgoers looking up as the sky suddenly turned dark and omnious from a tsunami-looking cloud covering the blue sky.
One social media user took to Twitter to share photos and videos of the phenomenon, showing how the cloud rolled across the sky horizontally, mimicking the curl of an ocean wave.
They wrote: “It was nuts to have experienced this rolling cloud in the north of Portugal. Felt like a tsunami out of a movie!”
“Apparently it was 150km long, stretching from Figueira da Foz all the way up to Vila do Conde, which is close to where I was,” they added.
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 formation is more common in the southern hemisphere, such as in Australia, and happens when cold air comes in contact with high temperatures. The roll sits low in the sky in a horizontal tube-shaped arcus cloud and is “relatively rare,” according to the National Weather Service (NWS).
“Roll clouds usually appear to be ‘rolling’ about a horizontal axis, but should not be confused with funnel clouds,” said NWS.
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 40C Sunday, with heavy rain, thunderstorms and even hail following the roll cloud.
Taking to the comment section of the Twitter post, several people shared their amazement in the weather phenomenon.
“NGL but I’ve never seen anything like it,” one user wrote, while a second person said: “Unusual and impressive.”
“That’s pretty wild! So fast, too,” a third person stated.
A fourth person claimed: “It started in Peniche! So, it was even bigger!”
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.