Britain faces a 'short-lived but quite intense' spell of hot weather this weekend with temperatures building up to the hottest day of the year so far by Monday.
Warm air will move up from Europe tomorrow and through Sunday and Monday when temperatures could hit 34C (93F), before conditions cool again on Tuesday.
England and Wales are expected to get to the low 30Cs (high 80Fs), with high teens (mid-60Fs) and low 20Cs (low 70Fs) forecast for Scotland and Northern Ireland.
Tropical Storm Debby, which battered parts of the southern US earlier this week, will contribute to the heat by shifting the jet stream - a current of strong winds in the atmosphere which has a significant influence on UK weather - further south.
But 'severe thunderstorms' and periods of heavy rainfall could also hit this weekend and Debby's interference could bring unseasonable winds to some western areas.
Holidaymakers enjoy the bright sunshine and warm weather at Bournemouth beach today
People walk along the promenade on Bournemouth seafront in Dorset this afternoon
Today began wet and cloudy in the South and East of England before drier weather brought sunny spells across much of the UK as the day progresses and temperatures warm up to 26C (79F) this afternoon.
Met Office spokeswoman Nicky Maxey said: 'The hot spell is short-lived but quite intense. Temperatures are due to peak on Monday and rapidly return to average on Tuesday and Wednesday.'
Much of the country will be cloudy and humid tomorrow morning with the North seeing brighter spells and light showers.
But this drizzly and overcast weather is expected to clear throughout the day with the mercury rising to 26C (79F) in the South East as the evening approaches.
Sunday and Monday are expected to be the warmest days, with highs expected to reach 33C (91F) in London, 26C (79F) in Manchester, 22C (72F) in Glasgow and 21C (70F) in Belfast.
The Met Office said: 'The highest temperatures are expected in parts of central, east and southeast England, peaking on Monday with maxima over 30C widely and possibly 33C to 34C in some places.
'This will be accompanied by some high night-time temperatures and humidity, especially on Sunday night in southern and western areas.'
But outbreaks of heavy rain and thunderstorms may accompany this hotter weather in central and northern parts of the country.
The high temperatures will see a rise in pollen count throughout the country, along with high UV levels.
The Met Office recommends covering up during midday hours and wearing sunscreen.
A high above 32.0C (89.6F) would also make it the UK's hottest day of 2024 so far, which is currently July 30 when that figure was recorded in London at both Kew Gardens and Heathrow Airport.
Met Office deputy chief meteorologist Dan Holley said: 'We expect to see a relatively brief hotter and more humid spell of weather for Sunday and Monday, before these hotter conditions recede on Tuesday, allowing more unsettled conditions to return.
'This change to hotter conditions is caused, in part, by the effects of Tropical Storm Debby in North America. Debby is helping to strengthen the jet stream, causing it to meander over the Atlantic.
'This will allow hot air over France to move into the UK later this weekend, and early next week.'
The Met Office says a warm snap is considered a heatwave if a location records at least three days in a row with maximum temperatures exceeding a designated value.
This is 25C (77F) for most of the UK - rising to 28C (82F) in London.
Given that highs of over 28C are expected in London only on Sunday and Monday, before a return to 25C on Tuesday, the warm period can unofficially be defined as a 'mini heatwave'.
Mr Holley added: 'Along with the rise in temperatures, there is also an increasing threat of heavy rain and thunderstorms on Sunday night and into Monday.
'This looks most likely across portions of Wales, northern England, Northern Ireland and southern and eastern Scotland.'
The South East could also still be very warm on Tuesday, but forecasters expect the hot air mass will become displaced by fresher conditions.
Unsettled weather is then expected to follow again, with occasional Atlantic frontal systems or showers moving through – although there will be sunshine too with temperatures returning closer to average.
Tropical Storm Debby, which is currently hitting eastern states of the US, is helping to strengthen the jet stream and make it 'meander' over the Atlantic which will allow hot air to move into the UK from Sunday.
Debby made its first landfall along the Gulf Coast of Florida on Monday morning as a Category 1 hurricane, before a second landfall yesterday in South Carolina as a tropical storm. At least seven people have died due to the storm.
The top temperature in the UK yesterday was 24.8C (76.6F) at Neatishead in Norfolk.
