Temperatures are expected to hit 44 degrees Centigrade (111 Fahrenheit) in Spain and Portugal on Wednesday as the two countries boil under their third heatwave of the summer.
With huge forest fires raging across southern Portugal for the fifth successive day, Spain's weather service warned that the average temperature across the country could hit a 70-year record.
"This will probably be the hottest five August days in 73 years," said AEMET, the state meteorological agency, with almost the whole country under red weather alerts.
Winds and extreme heat are also driving fires that have devastated 15,000 hectares of trees in neighbouring Portugal over the past few days.
The biggest blazes are in the southern Odemira region, where more than 1,500 people have been evacuated with the fires reaching the Algarve, a hugely popular tourist destination.
But firefighters tackling the wildfires said they were bringing them under control Wednesday, with a fall in temperatures and greater humidity at the coast helping stem the spread as hot air moves east.
Experts say the recurring heatwaves, which have been getting longer and more intense, are a consequence of climate change.
The Iberian Peninsula is bearing the brunt of climate change in Europe, with droughts and wildfires becoming more and more common.
Spanish firefighters were using up to a dozen water bombers to slow the spread of the flames around Valencia de Alcantara in Extremadura close to the border with Portugal.
"We evacuated our clients to a hotel in Alcantara," said Joaquin Dieguez, the owner of a holiday cottage. "But we are really worried because we have an enormous forest here with century-old oak trees. It's awful," he added.
First estimations suggest that 350 hectares of trees have gone up in smoke. The blaze comes after 573 hectares were destroyed in wildfires in Portbou in Catalonia in the northeast, with 450 acres of trees lost by another fire near Bonares in Andalusia in the south.