Holidaymakers travelling this weekend have been warned to expect flooding, thunderstorms and 55mph gusts of wind.
The Met Office issued a yellow warning for Saturday - with heavy rain likely to cause some disruption across the southern half of England and Wales.
Campsites may face high winds while cars towing caravans could face tricky driving conditions.
The thunderstorms come after days of high temperatures, which prompted Met Office warnings for extreme heat.
As the heatwave broke on Friday, there were warnings of strong, gusty winds particularly in exposed coastal areas and hilly places.
Thunderstorms were forecast to move into southern England overnight, reaching south Wales and the Midlands early on Saturday.
Frequent lightning and the possibility of large hailstones falling as well as torrential rainfall were likely, the Met Office said.
Firefighters were called to a house in Andover, in Hampshire, on Friday night after it was struck by lightning and its roof was partially destroyed.
Forecasters warned of a chance of flooding and power cuts - with up to 35mm of rain predicted to fall within in an hour in southern counties of England, and further slow-moving thunderstorms forecast to develop on Saturday afternoon.
Further heavy showers and thunderstorms are expected on Sunday across southern and eastern England, with the yellow warning stretching into East Anglia, possibly affecting Latitude Festival in Suffolk.
Up to 80 or 100mm of rainfall could build up in some locations over the course of the day, the Met Office says.
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