The Met Office has issued two weather warnings for thunderstorms later today.
The yellow weather warnings cover London, much of England's south, southwest and southeast, as well as Cardiff and southern Wales.
Heavy rain is expected, with a chance of thunderstorms, according to the first of the warnings, which covers Wales and large parts of southwest England between 8pm tonight and 8am tomorrow.
Thunderstorms are likely later this evening and overnight in London, Brighton, Oxford and other areas covered by the second warning, which comes into effect at 11pm tonight and lasts until 6am tomorrow.
There will be a risk of sudden flooding and power blackouts in both affected warning areas, the Met Office warned.
It added there is also a chance of hail and strong winds.
Flooding and lightning strikes could cause travel disruption on the roads, the forecaster said, including delays and cancellations to rail and bus services.
The Met Office website advises those looking to travel to check road conditions if driving.
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Tap hereSpells of heavy downpours are expected this evening and overnight.
Around 2cm to 4cm of rain is expected to fall, with 5cm possible in some places.
"Much of this rain may fall over a 2 or 3 hour period," the forecaster said.
Met Office meteorologist Alex Deakin said: "You may well get woken up tonight by a rumble of thunder, or some flashes of lightning across parts of the south.
"A lot of heavy rain falling in a short space of time as well."
He said it could create a lot of spray and surface water on the roads for commuters on Thursday morning.
Elsewhere, it will stay dry with temperatures mostly holding up in double figures across England and Wales - and around 8C to 9C in towns and cities further north.
He added: "A cloudy start then to Thursday one way or another, still some heavy bursts of rain early on across the South West.
"That should tend to clear away, but always the likelihood of further showers across southern parts of England, Mid and South Wales."
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