Another scorching September day will greet parts of England and Wales today before the summer heats turns to downpours.
The mercury is predicted to peak at 30C in London as the sunshine sweeps over central, eastern and southern parts of England.
The rest of England and Wales should enjoy temperatures of between 23C and 25C, while Scotland and Northern Ireland will have to settle for a cool but dry day.
Yesterday the hottest temperature of 28.8C was recorded in St Helier, Jersey, with Heathrow in west London coming in at 28.5C.
But from tomorrow the latest mini-heatwave will be replaced with thunderstorms, torrential rain and a risk of flooding.
Nick Prebble, a forecaster for MeteoGroup, the weather division of the Press Association, said: "It's going to be another hot day today, probably a touch hotter than yesterday.
"It will feel warm across England and Wales but getting cooler further north and particularly in Scotland and Northern Ireland.
"But the nice few days of sunshine will turn to rain tomorrow. There will be showers across the UK and the north will see heavy, persistent downpours with the potential of torrential rain and flooding.
"The unsettled weather and risk of showers will linger across the weekend."
Thousands of revellers who are making their way to one of the last big parties of the summer at Bestival are likely to only enjoy dry and sunny weather today.
From tomorrow the potential for showers will hang over the festival on the Isle of Wight until it finishes on Monday morning.