The boost in temperatures will come as a strong southerly airflow develops into Tuesday.
With unusually hot air across France and Spain – where temperatures have widely been in excess of 30C – the southerly wind will bring some of this warmth to the UK.
Temperatures across England will exceed 20C widely with the highest temperatures in south-east England where it will get into the mid-20s Celsius.
Average temperatures across England in late September are around 16 to 19C.
While there could be a lot of cloud with a few showers on Tuesday morning, sunny spells will develop over England and Wales.
It will also be warmer than average across Wales, Northern Ireland and Scotland with maximum temperatures on Tuesday of 17 to 22C.
However, after starting sunny here, cloud will increase during the day.
The southerly winds will strengthen with gusts up to 50mph expected in Northern Ireland and western Scotland.
This is linked to a large and deep area of low pressure moving north in the eastern Atlantic toward Iceland.
