The Met Office has issued a yellow warning for thunderstorms across the East of England.
The warning covers the whole region – from the Norfolk coast to west Northamptonshire – between 10:00 BST and 03:00 on Wednesday.
The Met Office said heavy showers were expected and added that driving conditions could become difficult along with some short term loss of power “likely”.
A spokesperson said: “Whilst some areas will miss these, where they develop 20mm (0.8in) and 30mm (1.2in) of rain [will fall] within two to three hours.”
The spokesperson added there was a “small chance” some locations could receive between 40mm (1.6in) and 50mm (2in) of rain over a longer period, especially across the south-east of the region.
They said: “If you find yourself outside and hear thunder, protect yourself by finding a safe enclosed shelter (such as a car). Do not shelter under or near trees, or other structures which may be struck by lightning. If you are on an elevated, area move to lower ground.”
The Met Office advised that property owners should check whether flooding in their area was likely and should prepare an emergency flood kit.
It also warned commuters that delays to train services were possible, while motorists were advised to check road conditions and amend travel plans if necessary.