There is a 20 per cent chance that the June temperature record of 35.6C, set in 1976 and 1957, could be met or exceeded.
A second amber heat health alert has been issued for London, the East Midlands, South East, South West, and East of England, effective from Friday to Tuesday.
The UK Health Security Agency also issued a yellow alert for Yorkshire and Humber and the West Midlands, warning of significant impacts on health and social care services.
The Met Office attributes the warm conditions to south-westerly winds drawing humid air, advising the public to take precautions, especially for vulnerable individuals, due to high UV and pollen levels.