Setúbal, Lisbon and Leiria will be under the warning due to the persistence of high maximum temperatures until 18:00 on Sunday.
The maximum temperatures in mainland Portugal 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.
From today onwards, the weather on the continent will be influenced by an “intense anticyclonic ridge located over Western Europe, associated with the transport of a mass of hot and dry air, originating in North Africa”.
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.
The hot weather is expected to persist at least until Tuesday.