Parts of eastern England may reach up to 30C on Friday, but the Met Office has warned of thunderstorms later that evening.
Cambridge is forecast to reach 29C, while temperatures are expected to reach 27C in Canterbury and 25C in Nottingham and Durham.
In Scotland, Aviemore could hit 24C as Met Office meteorologist Alex Deakin said much of Friday would be “hot and humid” with a “small chance” temperatures could reach 30C.
Temperatures of 30C would make it the hottest day of 2025, surpassing the 29.3C recorded at Kew Gardens in west London on May 1.
It means the parts of the UK could be hotter than Ibiza, Mykonos and Los Angeles.
“A good chunk of England and southern Scotland will be dry for most of Friday,” said Mr Deakin.
He said “beefy showers” were expected on Friday in Wales and the west of England after “a humid start to what will be a very warm day for some on Friday”.
Moving into Friday evening, a yellow weather warning is in place for London, Wales, England’s east and south east, east and south west, as well as the West Midlands, with the Met Office warning they could cause disruption overnight.
“It will be cooler in the far south-west, particularly as the heavy downpours arrive in the afternoon,” Mr Deakin said.
He also warned of hail, gusty wind and the possibility of flooding as the skies cloud over.
While many areas within the warning zone may escape severe weather, torrential downpours could bring 30–50mm of rain in a short time before conditions ease on Saturday morning.
Cardiff, Plymouth, Bath, parts of Greater London, Brighton and Norwich were among the areas included in the warning.
Mr Deakin said there was “a bit of uncertainty” over Saturday, but predicted “heavy rain” in the north of England’s, Northern Ireland and parts of Scotland as well as afternoon thunderstorms further south.
The UK Health Security Agency (UKHSA) has issued its first yellow heat-health alert of the year, running until 8am on Sunday in the east of England, East Midlands, London, and the south east.
Under UKHSA and the Met Office’s Weather-Health alerting system, a yellow alert means there could be an increased use of healthcare services by vulnerable people.
It may lead to an increase in risk to health for individuals aged over 65 or those with pre-existing health conditions, including respiratory and cardiovascular diseases.
