A yellow thunderstorm warning will come into force this morning – with heavy rain, lighting and hail set to hit parts of southern England.
The alert, covering areas including Bristol, Oxford, Southampton, London, Kent and Ipswich, will be in effect from 10am to 9pm.
Forecasters have said downpours could dump up to 60mm of rainfall within two hours in some places.
They also warned of possible flash flooding, public transport disruptions, road closures and power cuts.
Check the latest weather forecast where you are
Met Office meteorologist Clare Nasir said: “Expect some heavy weather coming towards central and southern parts of England and Wales through the next 24 hours.
“A thunderstorm warning has been issued for southern counties of England, all courtesy of this feature running down from the Republic of Ireland into Thursday, bringing more clouds, some showery bursts of rain turning heavy and thundery, with lightning as well as hail.”
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Ms Nasir added there will be some “fine weather” further north, and sunshine in the afternoon for Northern Ireland, western Scotland and Wales.
Thunderstorms are expected to clear into Friday morning.
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The Met Office advises those who expect to be affected to prepare an emergency flood kit and check to ensure movable objects or temporary structures are well secured ahead of the gusty winds.
Further heavy showers are set to hit the East of England on Friday, as well as northern and northeastern Scotland.
But many places in the west and southwest of the UK could stay dry and see some sunny spells.
On Saturday, the risk of showers across the country is minimal, while on Sunday, the heavy rain could reappear, particularly in the North West of England.