An area of warm, very humid air is expected to move northwards from France into southern Britain late on Thursday and into Friday.
Temperatures are expected to peak in the low to mid 20s°C on Friday before isolated severe thunderstorms develop.
This will be succeeded by a band of more widespread heavy rain and occasional thunderstorms.
These will move gradually north later in the day, affecting much of the eastern region until around 7am on Saturday morning. The Met Office are warning the public to be aware of the chance of, in particular, surface water flooding causing localised disruption along with lightning and hail.
The forecast is correct at noon on Wednesday, June 10.
See the latest Met Office weather warnings at metoffice.gov.uk.