Thunder and lightning have been forecast, along with heavy overnight downpours across Brighton and Hove.
Between a quarter of an inch and three quarters of an inch of rain is expected overnight, according to some forecasts.
And the Met Office said: “Thunderstorms developing over parts of England and Wales from early Sunday may cause travel disruption and, in a few places, flooding.”
The Met Office, Britain’s official weather forecaster, issued a yellow thunderstorm warning, covering the period from midnight to 6pm tomorrow (Sunday 5 June).
It said: “Thunderstorms and areas of rain are expected to develop over parts of England and Wales during the early hours of Sunday.
“Torrential downpours are likely in a few places, with parts of the Midlands, East Anglia and south east England most at risk.
“Some places could see 15mm to 20mm in an hour, and perhaps up to 50 mm before storms fade, and hail may affect a few spots.
“These thunderstorms will slowly spread into southern parts of northern England on Sunday morning before easing.
“Further south, drier conditions briefly develop on Sunday morning before further showers and thunderstorms develop over some parts of southern England, Wales, the Midlands and East Anglia later.
“These may give some heavy downpours, with a further 10mm to 20mm possible in some places.”
The BBC said the in Brighton and Hove the weather would be “cloudy with heavy showers drifting in from the south”.
It added: “Through the early hours it will turn rather wet with heavy and thundery downpours.”
