A thunder warning has been issued by the Met Office for this afternoon, with Brighton and Hove right in the middle of the affected area.
The warning, which was issued at 10.40am, says thunder will break out from 1pm to 11pm, moving slowly across the south east.
The warning says: “Whilst some places will escape them, thunderstorms will break out this afternoon and evening giving torrential downpours in a few places.
“Some of these storms will also be slow-moving, meaning that downpours may well be quite prolonged. 20 mm rain may fall in an hour and, in some places, 30 to 40 mm rain may fall in two or three hours.
“Thunderstorms will then slowly ease through the evening.
“Thunderstorms developing this afternoon may bring some travel disruption and flooding for a few places.
“Flooding of homes and businesses could happen quickly, with damage to some buildings from floodwater, lightning strikes, hail or strong winds.
“Fast flowing or deep floodwater is possible, causing a danger to life.
“Where flooding or lightning strikes occur, there is a chance of delays and some cancellations to train and bus services.
“Spray and sudden flooding could lead to difficult driving conditions and some road closures.
“Some communities might become cut off if roads flood.
“Power cuts might occur and other services to some homes and businesses could be lost.”