The wet weather will persist for parts of the country this week, with further downpours and thunder predicted for northern England, Scotland and Northern Ireland on Tuesday.
But temperatures will gradually build until Sunday, when they are expected to reach the high 20s across much of the UK – and even 30C in some isolated spots.
The warmest Bank Holiday Monday on record was 28.2C, set at Holbeach in Lincolnshire in 2017.
Met Office spokesman Grahame Madge told The Independent: “We’ve got quite humid air at the moment and that could lead to rainclouds and possibly thunderclouds on Wednesday across the Midlands and East.
“Apart from a few showers at the moment, the weekend looks very fine and clear.
“By Saturday or Sunday we are looking at highs of around 29C quite widely in the South and East, possibly something with a three in front of it in the odd isolated spot.”
Mr Madge said it was “possible” parts of the UK could experience a heatwave over the weekend, but that it was “more likely we will get more sporadic highs on different days in certain areas”.
He added: “For parts of the South East you would have to see three days of temperatures above 27C.
“It’s possible that we may get some locations falling within that threshold – but I would not want to say that it would be a widespread event.”
Bookmakers also cut the odds on Monday setting a new record to 2-1, from 3-1.
Met Office forecaster Emma Smith warned there will be “quite a few showers around” on Tuesday, with “a risk of a rumble of thunder or two”.
Showers are expected to continue in northern areas of the UK until Friday, with isolated outbreaks of rain also expected in some southern areas before high pressure moves in, bringing warmer and drier weather in time for the long weekend.
Central and southern England are expected to see the warmest weather of the bank holiday, while temperatures across northern areas of the UK will be lower, with conditions likely to be more changeable.
Average rainfall across England so far this month is 68.6mm.
Scotland (141.8mm), Wales (120.2mm) and Northern Ireland (103.1mm) have seen considerably more, but only Wales and Scotland have seen above average rainfall so far this month.
Rainfall for August, which is typically the wettest of the three summer months, is some way off the record-breaking levels of 1912 when 167.6mm fell.
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