The warning in the districts of Porto, Faro, Setúbal, Viana do Castelo, Lisbon, Leiria, Beja, Aveiro, Coimbra and Braga will be in effect between 09:00 on Friday and 06:00 on Saturday due to maritime agitation, with waves up to 4 to 5 metres expected.
The yellow warning for the north coast of the island of Madeira and Porto Santo will last between 12:00 pm on Friday and 00:00 am on Saturday.
The Portuguese Institute of the Sea and the Atmosphere (IPMA) also placed the islands of the Western (Flores and Corvo) and Central (Terceira, Pico, São Jorge, Graciosa and Faial) groups of the Azores under yellow warning until 15:00 today because of the sea turmoil.
Because of the maritime unrest, the Navy and the National Maritime Authority (AMN) warned on Wednesday of the worsening of weather conditions from 6:00 pm today and 6:00 pm on Saturday.
In a statement, the Navy and AMN say that the sea will be characterised by swells in the northwest quadrant, with a significant height that could reach seven meters and a maximum height of 13 meters.
Winds from the southwest quadrant are expected with an average intensity of up to 55 kilometers per hour and gusts of up to 100 kilometers per hour.