Thunderstorms and heavy rain could cause flooding, travel disruption and power cuts later today, forecasters have said.
The Met Office has issued a yellow weather warning from 4pm to midnight across much of South Wales, South West England and southern England.
Some areas could be hit by up to 40mm of rain falling within the space of two to three hours, the weather agency said.
It added there was a “good chance” that driving conditions would be affected by spray, standing water or hail, while train services may also be disrupted.
Flooding to homes and businesses is also possible, along with “some short-term loss of power”, the Met Office added.
Forecasters believe thunderstorms are most likely to occur in south-facing coastal areas, with hail and strong winds accompanying the heaviest rainfall.
Further heavy showers and thunderstorms are expected across central and southern areas of the UK on Tuesday and into Wednesday.
However, the weather service said it also had “increasing confidence” that ex-Hurricane Kirk will track to the south of the UK, bringing heavy rains and strong winds to northern France instead.
Although shifts to its path remain possible, the threat of a significant impact on the UK is now much reduced, it added.
It comes following a wet start to the month for much of the country, which has caused isolated flooding in some regions, including Norfolk.
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Frank Saunders, a chief meteorologist at the Met Office, said: “Areas of heavy showers and thunderstorms will move northwards across southern parts of England and Wales later this afternoon before clearing northwards overnight.
“It’s possible that some places could see 20 to 30mm of rain within two to three hours, with a small chance that a few places could receive 40mm.
“Thunderstorms are most likely for south-facing coastal districts, and hail and some strong gusts of wind could accompany the heaviest showers and thunderstorms.”
The Met Office said temperatures would fall from Wednesday in the north, with all areas experiencing below-average temperatures from Thursday.
Night frosts are also expected for some regions later in the week, with snow possible in higher areas of Scotland.
Yellow warnings are issued by the Met Office for “low level” weather impacts which could cause disruption in some areas – but also have the potential to become “much more severe”.
