The warning covers Bragança, Viseu, Évora, Guarda, Vila Real, Setúbal, Santarém, Lisbon, Beja, Castelo Branco and Portalegre.

The Portuguese Institute of the Sea and Atmosphere (IPMA) has issued the warning due to high maximum temperatures. It will be in force from Thursday, 3 September, until 7 pm on Friday, 4 September.

Temperatures are expected to rise across most of the country on 3 September, with maximums generally ranging from 34°C to 38°C.

The hottest conditions are forecast for inland areas south of Serra da Estrela, including the Tagus Valley, Beira Baixa and Alentejo, where temperatures could reach between 40°C and 42°C.

Coastal areas will be slightly cooler, with maximum temperatures expected to range from around 25°C or 26°C to 30°C or 31°C. The highest coastal temperatures are expected in the south.

IPMA also warns that dust carried from North Africa may reach southern parts of Portugal on 3 September.

The hot and dry conditions are also increasing the danger of rural fires. Thirty municipalities in the districts of Bragança, Guarda, Coimbra, Castelo Branco, Santarém, Portalegre and Faro are already facing a very high fire risk.

The fire risk is expected to become more widespread on 3 September, particularly across the interior North and Centre, Alentejo and the Algarve.

A yellow warning is the least serious of IPMA’s three warning levels. It is issued when the weather may present a risk for certain activities.