Britain's mini-heatwave is set to continue with a day of tropical temperatures ahead of a night of torrential thunderstorms expected to bring nearly a month's worth of rain.
Swathes of England and Wales are forecast to bake in temperatures clear of 30C (86F) on Tuesday while the mercury rises to 29C (84F) in Scotland and 28C (82F) in Northern Ireland.
But parts of the South East could see temperatures climb as high as 35C (95F) - close to the record for July of 36.7C (98.06F).
Meanwhile there is a yellow warning of rain stretching from Tuesday evening and into Wednesday evening, with up to 2in (50mm) expected in some parts, bringing a risk of flash flooding.
People are urged to drink plenty of water and avoid dehydrating alcoholic and caffeinated drinks, close curtains to keeps rooms cool, open windows and avoid people and animals being left in closed, parked vehicles which can get extremely hot.
There are also warnings to stay out of the sun between 11am and 3pm, avoid physical exertion at the hottest times of the day and stay in the shade - and to put on a hat and wear sunscreen.
Pollen levels will be high over the country for the next few days, causing havoc for hay fever sufferers - and there may be another restless night on Tuesday as temperatures reach 22C (71.6F) overnight.
The hot weather has been caused by a warm plume of air that has worked its way northwards from Spain, the Met Office said.
Wednesday will see highs reaching the low 30Cs, but by Thursday fresher conditions from the Atlantic will bring temperatures down to the more comfortable mid-20Cs, reaching around 22C (71.6F) to 24C (75.2F) by Friday and Saturday.
Met Office forecaster Sophie Yeomans said: "We are looking at probably the hottest day of the year today with quite a few places reaching 34C or even 35C in the South East.
"With all the warm and humid air it does mean we are going to have a thundery breakdown later on this evening. The only part to escape will be the very south of England, with lightning, hail, gusts of wind and 30mm of rain falling in the hour, but this won't be persistent. There's potential for nearly a month's rain in some areas during the time we have the warning."