The National Maritime Authority (AMN) has warned of a "considerable worsening" of weather conditions and sea conditions in mainland Portugal starting Tuesday, with waves as high as four metres and potentially reaching seven metres.

In a statement, the AMN indicated that these worsening conditions are expected between Tuesday and noon on Wednesday.

According to the authority, the sea conditions will be characterised by waves coming from the west-northwest quadrant, "with a significant height that can reach four metres and a maximum height of seven metres, with an average period varying between 15 and 17 seconds."

Winds are expected from the north, with average intensity of up to 38 kilometres per hour (km/h) and gusts of up to 69 km/h.

The National Marine Authority (AMN) has urged beachgoers to exercise caution when going to the beach, to frequent permanently supervised beaches, to respect flags and beach signs, and to follow the instructions of lifeguards and other lifeguards, to keep a close eye on children, and to avoid going under cliffs.

The National Marine Authority (AMN) advised the entire maritime community to reinforce moorings and maintain strict surveillance of moored and anchored vessels.

The general public has been advised to avoid walking along the seashore or in areas exposed to rough seas, such as harbour protection jetties, cliffs, or beaches, to avoid being caught by a wave.

The maritime authority also indicated that recreational fishing should not be practiced under these conditions, especially near cliffs and cliff areas frequently hit by breaking waves, "always keeping in mind that under these conditions the sea can easily reach seemingly safe areas."

The Portuguese Institute of the Sea and Atmosphere (IPMA) also warned today that 10 districts in mainland Portugal will be under a yellow warning on Tuesday and Wednesday due to the forecast of strong sea agitation, an uncommon occurrence in August and a result of the positioning of post-tropical cyclone ERIN.

The districts of Porto, Faro, Setúbal, Viana do Castelo, Lisbon, Leiria, Beja, Aveiro, Coimbra, and Braga will be under a yellow warning between 6:00 a.m. on Tuesday and midnight on Wednesday due to rough seas, with forecast waves of up to four meters from the northwest.

According to the Institute, during the afternoon high tide period, combined with a predictably high tidal range, several beaches may be left without available sand.

The IPMA also indicated that the Algarve coast will not be as exposed to this situation, but swells will remain strong on the west coast throughout the week, with significant heights between two and three metres.