“Meanwhile England and Wales will be sunnier, especially today with temperatures widely above 25 Celsius.
“It’ll turn hot in southern and eastern areas with temperatures reaching around 30 Celsius in a few spots, possibly 31 Celsius on Tuesday.”
Mr Saunders added: “On Wednesday a cold front will slowly sink southwards, bringing cloudier skies and temperatures closer to average for northern parts of the UK, but southern areas will still see plenty of sunshine and temperatures in the mid- possibly high-20s Celsius, which could meet heatwave criteria in a few locations.”
The heatwave will be the longest September warm spell in the UK since 2016.
Back then, temperatures reached 34.3C at Gravesend on September 13.
Tonight will, according to the Met Office “be warm for many in towns and cities, with temperatures of 16 to 19C” southern and central areas, but higher temperatures are expected on Tuesday.