Lightning strikes, hail, torrential rain and flash flooding have caused major travel problems across east and south-east England.
There have been problems on the roads in Sussex, Essex and London.
London Fire Brigade said it was helping people trapped in their cars across parts of the capital.
Southern Water said "torrential rain fell across Sussex" leading to some sewers becoming "overwhelmed by the sheer volume of water".
Electrical supply problems caused by a lightning strike had led to disruption on Southern railways, although a Network Rail spokesman said services were returning to normal, subject to some residual delays.
Southern said it was running normal services in the region, apart from trains to Brighton which are not stopping at Worthing because of flooding in the station subway.