Temperatures of up to 33C (91F) could hit parts of the country this weekend in a “short-lived but quite intense” spell of hot weather.
Warm air is set to move up from Europe on Saturday, through Sunday and into Monday, bringing with it the hotter weather.
England and Wales are expected to see temperatures in the high 20s and low 30s.
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Meanwhile, Scotland and Northern Ireland are forecast to see temperatures in the high teens and low 20s.
The hot spell is due, in part, to the tropical storm Debby which hit the US this week.
As the storm breaks down, it will influence the jet stream, the Met Office previously said, helping play a role in the coming hot weather.
Met Office spokeswoman Nicky Maxey said: “The hot spell is short-lived but quite intense.
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“Temperatures are due to peak on Monday and rapidly return to average on Tuesday and Wednesday.”
Check the weather forecast where you are
Weekend forecast
Much of the country will see a cloudy and humid start to Saturday morning, with the North seeing brighter spells but light showers too.
The clouds are due to clear up through the day, with warmer air moving in on Saturday evening.
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Sunday and Monday are expected to be the warmest days – with highs of 31C (88F) in London, 25C (77F) in Manchester, 22C (72) in Glasgow and 21C (70F) in Belfast.
Along with high temperatures the pollen count and UV levels will rise too.
Due to the short spell of the coming hot weather, it fails to meet the criteria for a heatwave.