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.

This is the moment a rare phenomenon was spotted at a beach in Portugal, as the country faces a heatwave with highs of 42C. Beachgoers on Sunday (29 June) were shocked when they saw a “roll cloud” coming out of the ocean and heading towards the shore.