The warning covers the districts of Viana do Castelo, Braga, Porto, Aveiro, Coimbra, Leiria and Lisbon, which will first be under yellow warning between 12:00 and 21:00 on Thursday, then orange.
The orange warning will last between 21:00 on Thursday and 18:00 on Friday, with northwest waves of 5 to 6 metres expected, reaching a maximum height of 10 to 11 metres.
The districts of Setúbal, Beja and Faro will also be under a yellow weather warning between 03:00 and 18:00 on Friday because of the rough sea, with waves from the northwest of 4 to 5 metres expected.
The maritime agitation also led the IPMA to issue a yellow warning valid between 06:00 on Friday and 06:00 on Saturday for the north coast of the island of Madeira and Porto Santo.
The orange warning is the second most serious and represents a moderate to high risk weather situation.