According to naval commander, vice-admiral Gouveia e Melo, who on Tuesday gave a news conference on the situation, the adverse conditions at sea are comparable to the storm dubbed 'Hercules' that in 2014 brought huge waves that hit the Azores first and then mainland Portugal.

Gouveia e Melo explained that “the eye of the hurricane” would pass the Azores on Wednesday - with waves of up to 12 metres expected - and then reach the mainland on Thursday, with waves of eight metres, and the island of Madeira, with waves of six metres.

"It is comparable to storms of the past [such as Hercules]," he said. "We're increasingly seeing this kind of cyclones passing further south, hitting the Azores and the north of the Iberian peninsula."

The navy will, he said, be stepping up its usual operations to respond to the need for search and rescue operations at sea, with a oceanic patrol vessel in the central group of the Azores islands.

On the mainland there will be an extra corvette in the northern maritime zone, a corvette at Sines, a frigate at the ready at the Lisbon naval base, and three rapid launches on the south coast of the Algarve.