Britain is expected to bask in its hottest days of the year so far today and tomorrow, forecasters said.
Temperatures will reach a high of 26C (78F) today before possibly hitting 30C (86F) tomorrow, according to MeteoGroup, the weather division of the Press Association.
But high humidity means many areas could see rain and thunderstorms tomorrow morning and evening and sunshine struggling to break through the cloud.
Brendan Jones, senior forecaster at MeteoGroup, said the weather was being carried by warm air coming up from the Continent, with Germany, France and the Low Countries seeing temperatures soar past 30C (86F) in the past few days.
"It does look as if today and tomorrow are going to be very warm," he said.
"I think today will be the hottest day of the year and tomorrow will break that again."
Temperatures should be high across England and Wales, with the South East seeing the highest temperatures, he said.
Revising a series of depressing forecasts, the Met Office predicted a heatwave that will bring the hottest day of the year as thermometers reach 27C today.
“This is going to be a warm week and Wednesday will easily be the hottest day of the year so far,” a Met Office spokesman said, adding that the sudden change of fortune has been caused by a stretch of good weather on the Continent.
“The warm weather that France and Spain have been experiencing recently is being dragged over Britain. We believe that temperatures will be between 26C and 28C, and will feel very warm and humid. But it will not be wall-to-wall sunshine; it will be mainly cloudy with a chance of thunderstorms.”
“We are going to see warmer air, but it’s not going to be unbroken sunshine and it’s going to be very humid as well. If the sun breaks through we could see 25 or 26 degrees tomorrow.”
But last week the Met Office played down the chance of a warm spell and forewarned a return to the wind, rain and cold that blighted spring. Speaking to The Independent then, a spokesman said “typical British weather” of sporadic showers and brief sunny spells would prevail until next week.
The changing forecast adds another upset in several years of increasingly volatile British weather. Indeed, so unpredictable has our climate become that the Met Office has organised a summit to discuss seasonal variability at their headquarters in Exeter tomorrow.
The meeting will see leading meteorologists and scientists consider the reasons for phenomena including the summer floods in 2012, the freezing winter of 2010 and the widespread snow in May this year.
“We have seen a run of unusual seasons in the UK and northern Europe, such as the cold winter of 2010, last year's wet weather and the cold spring this year,' a Met Office spokesman said.
“This may be nothing more than a run of natural variability, but there may be other factors impacting our weather.”