The State Meteorological Agency (AEMET) reports that temperatures will reach between 39C and 41C in Cordoba, Granada and Jaen, and in the centres of Malaga, Huelva and Sevilla.
All have been placed on orange alert.
Antequera will reach 38C from noon until six in the afternoon.
In the Serranía de Ronda thermometers will reach up to 36C.
There are yellow alerts -between 39 and 34 degrees – in Huesca, Teruel and Zaragoza (Aragon); Ávila, Soria and Salamanca (Castile and Leon); Lleida (Catalonia), Madrid, Cáceres and Badajoz (Extremadura); Murcia and the islands of Ibiza, Formentera and Mallorca.