Experts at the Met Office have issued five severe thunderstorm warnings covering most of the UK.
The yellow weather alerts are in place for large swathes of England and Wales throughout Thursday to Monday.
Forecasters say there's a slight chance of flooding, and travel disruption is expected.
They also warned 'deep floodwater' could develop, and there's a slight possibility of power cuts.
If flooding occurs, road closures are possible, with long delays and cancellations to bus and rail services, Wednesday's warning says.
A predicted 30-40 mm of rain may fall in less than an hour, with a small chance of 60 mm falling in an hour and 70-100 mm in two to three hours.
There will be more heavy rain on Friday (Image: MET OFFICE)
On Friday, Saturday, Sunday and Monday more heavy showers and thunderstorms are expected at times, which may lead to some flooding or travel disruption.
There is a small chance that some homes and businesses could be flooded quickly, with damage. The Met has not issued a threat to life warning.
It will feel slightly cooler in Bristol today, with the mercury peaking at 27C. By Friday, temperatures should drop to 23C.
UK weather forecast
Thursday:
After a dry and cloudy start, further thundery showers will develop during the morning interspersed with sunny spells. Another very warm and muggy day. Maximum temperature 28 °C.
Outlook for Friday to Sunday:
Thundery showers are likely to persist through the weekend with a brief interlude of drier conditions on Saturday. Staying very warm.
