The Met Office has expanded a yellow weather warning for thunderstorms – with larger parts of England and Wales affected.
Forecasters say torrential downpours could cause travel disruption, and flooding is also possible.
The weather warning area has been expanded westwards and northwards, and is in force until 11.59pm tonight.
Where thunderstorms do occur, up to 40mm of rain could fall in as little as one hour – rising to 60mm over a two or three-hour period.
“These torrential downpours may be accompanied by frequent lightning, whilst gusty winds and hail may also affect a few places,” the Met Office alert added.
The thunderstorms are mainly expected to happen in the afternoon and early evening, with forecasters warning their exact location “will be hard to pinpoint”.
Thunderstorm warning issued by Met Office for southern England with torrential rain expected
UK weather: Hottest day of the year recorded again as temperature goes above 32C
UK weather: Forecasters suggest when sun will return – as hottest day to give way to rain and plunging temperatures | Weather latest
Changes to the warning area are possible in the hours ahead.
Revellers at Glastonbury have been told they may need to take shelter as the thunderstorms sweep the country.
Festival attendees were told to pack for all eventualities – light showers are predicted on Friday and Saturday, with heavier rain on Sunday.