Higher than usual summer temperatures are expected in all of Spain's mainland provinces except for Galicia, Asturias and the north-east of Castile and León.
In what newspaper are calling 'an African heat wave', temperatures are expected to top 39 degrees in many place in the southern half of mainland Spain and in the Ebro valley.
These temperatures could reach 41 degrees in Andalusia's Guadalquivir valley.
Meanwhile, temperatures could climb above 36 degrees in many areas of northern central Spain.
Minimum temperatures are also unlikely to drop below the 20-degree threshold during the heat wave.
The high temperatures are expected to come down on Friday in the east of mainland Spain and on Saturday across the mainland.