On Thursday, running from midnight until 1pm, an area stretching from Plymouth into Wales could see disruption due to heavy rain and thunderstorms.
There is also a thunderstorm warning for Northern Ireland, running from 6am until 9pm on Thursday.
A new warning comes into force at 3pm on Friday for an area stretching from East Anglia into London and across parts of the South East.
It runs until 6am on Saturday and warns of disruption from thunderstorms.
The conditions could bring flooding to roads and properties, disruption to travel networks, and power cuts, said the Met Office.
Forecasters also warned of lightning strikes, hail and strong winds.
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