More than 40 municipalities in the districts of Santarém, Faro, Portalegre, Castelo Branco, Guarda, Viseu and Bragança are at maximum fire risk.
The highest maximum temperature forecast for today will be reached in Évora with 38 degrees Celsius, followed by Beja, Faro and Castelo Branco with 37, Portalegre 36 and Bragança at 34.
The IPMA also placed several municipalities in all districts of mainland Portugal at very high and high fire risk.
According to IPMA calculations, the fire risk will remain high in some districts at least until Saturday.
Madeira also has a very high and high fire risk, depending on the region.
This risk, determined by the IPMA, has five levels, ranging from low to high, and the calculations are obtained from the air temperature, relative humidity, wind speed and amount of precipitation in the last 24 hours.
Due to the heat, the IPMA has issued a yellow warning for the districts of Bragança, Évora, Guarda, Faro, Setúbal, Beja, Castelo Branco and Portalegre until 6:00 pm on Wednesday.
The Madeira archipelago is also under an orange warning until 6:00 pm today, then changing to yellow until 6:00 pm on Tuesday due to the hot weather.
The orange warning is issued by the IPMA whenever there is a "meteorological situation of moderate to high risk" and the yellow warning when there is a risk situation for certain activities depending on the meteorological situation.
The IPMA predicts for today on the mainland partly cloudy or clear skies, temporarily with cloudiness on the coast, sometimes strong winds from the north on the western coastal strip and in the highlands and morning fog or mist in some places on the western coastal strip.
The minimum temperatures will range between 15 degrees (in Braga and Viana do Castelo) and 24 (in Faro) and the maximum temperatures between 24 (in Aveiro) and 38 (in Évora).