Britain will be hotter than Portugal's Algarve coast from Wednesday (June 10) with temperatures soaring to 27C by Friday (June 12).
But the brief heatwave may not last with three days of thunderstorms threatening floods, travel disruption and a washout Isle of Wight Festival.
The Met Office said warm air from the Azores would send highs leaping from 18C on Tuesday (June9), to 20C on Wednesday, and rising to around 27C on Friday.
Britain will be hotter than 23C Faro, Portugal, for 48 hours, and even the North is due to nudge 22C on Friday.
Met Office forecaster Dan Williams said: “Warmer air from the Azores will see temperatures rise, with Thursday forecast 24C and Friday potentially in the ballpark of the hottest temperature of the year.”
Weather Channel forecaster Leon Brown said: “Temperatures will lift on Thursday up to 25C in Hampshire and Dorset, with Friday seeing temperatures as high as 27C in the South East.”
But the Met Office said three days of thunderstorms in the South and Midlands start on Thursday - amid warnings of flooded roads and lightning.
Washouts threaten 55,000 music fans at the Isle of Wight festival, starting Thursday.
MeteoGroup forecast up to 30mm of rain in the South on Friday.
Forecaster Dan Williams said: “Thundery showers will probably cover a larger area than last Friday, and last for a longer period.
“Thundery showers look like arriving on Thursday afternoon in the South-West and lasting until Saturday morning in the South and Midlands, with the thundery risk continuing on Saturday.
“We’re keeping an eye on severe weather warnings due to possible travel impacts.
"Heavy thundery showers see a lot of rain fall in a short time and could cause standing water on roads.
“People heading to the Isle of Wight Festival should keep up to date with forecasts and pack accordingly.
"It is in the thundery showers risk area from Thursday to Saturday morning.”
Meteorologist Mark Stephens-Row of Weather Services International, the Weather Channel’s business division, said: “We expect week-long periods of un-summerlike wet weather.
"Unsettled conditions may coincide with Glastonbury and Wimbledon.
"But highs up to 33C are expected, most likely in late July and early August.”
Originally published on Mirror Online.