A large swathe of western Europe is bracing for the first significant heat event of the summer, with temperatures forecast to rise to more than 10C above the norm and new monthly records for May expected to be set in possibly hundreds of places.

Temperatures across Portugal, Spain, France and the UK were expected to exceed 30C (86F) on Friday and into next week, reaching 32C in Paris and London and 35C in south-west France, with highs of up to 38% in the Guadiana and Guadalquivir regions of Spain.

“Both maximum and minimum temperatures are likely to reach unprecedented levels for the season in multiple regions, particularly the south-west, during a premature heat event that will be intense and last several days,” said Météo-France.

The French national weather forecaster said new records were almost certain to be set for the highest May temperature recorded in France (30.5C in 2025), and the highest average temperature across the country on a day in May (22.8C in 2017).

It said the exceptional temperatures, likely to exceed previous records by three or four degrees in some cities such as Nantes and Brest, were caused by a heat dome, with hot air from Morocco trapped under the high pressure of a powerful anticyclone.

Météo-France said the temperatures expected in Brittany in particular were “quite remarkable so early in the pre-summer season”, and likely to exceed existing records by as many as three or more degrees.

It said climate breakdown meant that Europe, the world’s fastest-warming continent, could expect to see such exceptional heat events happen “more and more often and more and more prematurely, and to be more and more intense”.

The Met Office said temperatures in the UK, where “extraordinary” heat health alerts have been issued for the weekend, could reach 33C locally on Monday, exceeding the current highest temperature recorded in May of 32.8C, set in 1944.

Parts of the UK could also enter a heatwave, with temperatures exceeding 26C to 28C – depending on the location – for three days. That is unlikely in France, where night-time temperatures must also stay above a certain level for an official heatwave to be declared, or Spain, where temperatures would have to reach high summer levels.

In Spain, where temperatures already reached 38C on Thursday, the heat claimed the life of a two-year-old girl who died in the northwest region of Galicia after accidentally being left in her father’s car for hours.

The state meteorological office, Aemet, said the hot spell was expected to stretch well into next week and could bring record May temperatures. “Full-on summer heat is the phrase that best describes the weather we’ll see across most of Spain over the coming days,” said Aemet spokesperson Rubén del Campo.

“Temperatures will be between 5C and 10C above the seasonal average – and 10C above average for the time of year in northern regions. These are the kind of temperatures we normally see in July and August.”