Forecasters say the hottest conditions are likely between Monday and Wednesday as a large high-pressure system settles over the Iberian Peninsula, drawing very warm, dry air northwards from North Africa.

Several inland areas are expected to see temperatures ranging between 35°C and 40°C, particularly in parts of the Alentejo, the Guadiana Valley, and sections of the interior north and centre of the country. Mértola is among the locations that could approach the highest temperatures during the middle of the week.

Meteorologists describe the event as a “heat dome”, a weather pattern in which a persistent area of high pressure traps hot air close to the surface for several consecutive days. The phenomenon can lead to temperatures significantly above seasonal averages and make heatwaves more prolonged.

Current models suggest some areas could experience temperatures more than 10°C above normal for late May.

The weather system is also expected to carry dust from the Sahara into Portuguese skies during the week.

While much of inland Portugal faces intense heat, coastal regions in the north and centre are likely to remain noticeably cooler because of Atlantic influence, with temperatures generally staying between 20°C and 25°C.

Forecasters believe the warm conditions could continue into the final days of May as the high-pressure system remains in place across parts of western and central Europe.