The hot weather will intensify and be more widespread on Wednesday.
In an area from South Yorkshire to east Wales, Somerset and east across England temperatures will be in excess of 30C.
Some of the warmth will spread further north into northern England, Scotland and Northern Ireland with temperatures into the low to mid-20s.
The hottest weather will be around the Midlands and south-east England with 31 to 33C.
By Thursday and Friday, extreme heat is most likely in parts of the Midlands, eastern and south-east England where temperatures could be as high as 35 or 36C.
As heat builds throughout the week, overnight temperatures will stay relatively high bringing some uncomfortable nights for sleeping.
Minimum temperatures may not go lower than 16 to 18C across England and Wales.
There is also a possibility of a “tropical night” – where temperatures remain above 20C all night – in south-east England.
While the heat will not be quite as intense or feel as humid as the heatwaves in June and July, the understands the Met Office may be considering issuing extreme heat warnings.
That would suggest that, as well as health impacts, there could be some concerns about infrastructure such as the transport network and power lines.
The highest temperatures in June and July were 38C and 35.5C respectively.
For the first time in recorded history we are expecting a temperature higher than 35C to have been recorded in the UK for four consecutive months – underlining that this has been a year like no other.