The districts of Porto, Setúbal, Santarém, Viana do Castelo, Lisbon, Leiria, Aveiro, Coimbra and Braga will be under the yellow warning due to the persistence of high maximum temperatures until 11pm on Sunday.
The north and south coasts of the island of Madeira and Porto Santo have been under a yellow warning since Thursday, lasting until 11pm on Sunday.
The maximum temperatures on the continent will be above 30 degrees Celsius from today onwards, reaching 37 degrees, around 5 to 8 degrees above the average for the month of September, according to IPMA.
According to IPMA, maximum temperatures are expected to reach values between 35 and 37 degrees, particularly in the southern region and the Tagus Valley.
Minimum temperatures will also rise, and nights with values equal to or greater than 20 degrees may be recorded in some places, especially on the coast of the Algarve region.
The IPMA has placed the municipalities of Aljezur, Lagos, Monchique, Portimão, Silves, Loulé, São Brás de Alportel and Tavira, in the Faro district, at maximum risk of rural fires on Saturday.
Another 20 municipalities in the districts of Faro, Beja, Santarém, Leiria, Portalegre and Castelo Branco will be at very high risk of fire.
This hot weather situation is expected to persist at least until Tuesday.