Warm air will be drawn up from the south thanks to the interaction between high pressure drifting across the south of the UK and an area of low pressure – containing remnants of Tropical Storm Dexter – in the Atlantic.
England and Wales will have the best of the sunshine, although a few scattered thunderstorms are likely. Northern Ireland and Scotland can expect outbreaks of rain at times, especially on Monday.
After a warm weekend, temperatures really start to climb on Monday.
Temperatures across much of England and Wales will rise to the mid to high twenties, with some locations in the Home Counties and London exceeding 30C.
This will be the first day of the heat where the official heatwave criteria is met across many areas.
For an official heatwave to be defined, there needs to be three consecutive days with temperatures above 25 to 28C, dependant on where you are in the UK.
With very warm and humid air around until Wednesday, that will make it the fourth heatwave of the summer, particularly for east Wales, the Midlands, eastern and south-eastern areas of England.
