The districts of Viana do Castelo, Braga, Porto, Aveiro, Coimbra, Leiria and Lisbon will be under yellow warning because of the sea turbulence, with northwest waves of 4 to 5 metres expected between 6pm on Thursday and at 3pm on Friday.
The yellow warning translates into risk situations for certain weather dependent activities.
The IPMA also placed the Bragança and Guarda districts until 6pm on 8 January under yellow warning because of the persistent fog in some places, with possible icicle formation and maximum temperature below 5/6 degrees Celsius.
The Institute foresees on 8 January in the northern and central regions a cloudy or clear sky, generally cloudy in Minho, in the transmontano northeast and Beira Alta until mid-morning.
From the afternoon, a gradual increase in cloudiness is expected in the coastal regions.
The forecast also points to light wind, temporarily moderate blowing from the north in the highlands of the Centre region, and severe night cooling, with frost formation, especially in the interior regions.
Morning fog or mist is expected, and may persist in some inland locations until mid-afternoon.
In the south it is expected to be cloudy or clear, increasing cloudiness on the west coast from late afternoon, and light wind, temporarily blowing from the north in the highlands.
IPMA also foresees marked night cooling, with frost formation, in the interior regions and morning fog or mist in some places.
Minimum temperatures on the continent will range from -2 degrees (Bragança) to 8 (in Portalegre) and maximums between 9 (in Vila Real) and 19 (in Faro).