The southeast of England is poised to be hotter than the Algarve, Mykonos and Crete, recording temperatures over 30C for three consecutive days on Tuesday, Wednesday and Thursday.
But before the sunshine breaks through, there is a danger of thunderstorms, heavy rain and localised flooding for some, forecasters say.
“Today, showers will develop across the southeast of England in the afternoon, some heavy and thundery,” Met Office meteorologist Mark Wilson said.
More showers will sweep across Wales, Northern Ireland and central and eastern areas, while the West of the country should remain mostly dry with sunny spells.
Temperatures will reach 25C in the south and 20C in Scotland.
The mercury will start to rise on Sunday, reaching 26C while much of the UK stays dry and sunny.
However, heavy showers are expected across western Scotland on Sunday. The Met Office has issued a yellow weather warning for heavy rain, which may lead to some localised flooding and travel disruption, according to the Met Office.
“But next week we’ll see some changes,” says Mr Wilson. “It will still rain in Scotland on Monday but much of the rain should be gone by Tuesday. It will stay dry elsewhere, with temperatures reaching highs of 28C on Monday.”
A heatwave should develop starting on Tuesday.
Chief Meteorologist at the Met Office Andy Page said: “As we head into next week temperatures will increase daily across much of England and Wales as hot air is drawn up from France and Spain.
“Temperatures could reach 34C by Wednesday in parts of central, southern or eastern areas and heatwave thresholds are likely to be reached in some places.”
A heatwave takes place if temperatures stay high in the same spots for three consecutive days, according to the Met Office.
London is predicted to see temperatures peak at 32C on Wednesday, while on Tuesday the mercury could rise to 28C in Manchester, 30C in Bristol, and 29C in Birmingham and Brighton.
On Tuesday, temperatures will also rise to 25C in Scotland and over 30C in Wales.
The hot and dry weather will continue into Wednesday and possibly Thursday, which would make the hot spell a heatwave.
However, rain might develop on Thursday bringing fresher conditions across the country.
The hot weather comes as a new heatwave is forecast to grip western Europe in the middle of next week, giving July 2019 a chance of being the hottest month ever recorded.
Temperatures will peak at 39C in Paris on Wednesday, while France Météo is forecasting temperatures over 40C in parts of the country.
It will also be 33C in Amsterdam and Berlin, 38C in Madrid and 36C in Rome.
Meanwhile, two-thirds of the US are also currently experiencing unusually hot, hazy and humid conditions, with temperatures reaching 38C.
US Climate scientist Michael Mann wrote on Twitter: “This is significant. But stay tuned for July numbers. July is the warmest month of the year globally. If this July turns out to be the warmest July (it has a good shot at it), it will be the warmest month we have measured on Earth.”
The new heatwave comes just three weeks after western Europe saw record-breaking temperatures in the end of June, when the mercury rose to 46C in France and in the high 30s across the continent.
Saturday 29 June was the hottest day of the year so far in the UK, with the mercury reaching 34C in Heathrow and Northolt in west London.
Additional reporting by PA
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