More than an inch of rain is expected to fall on Brighton and Hove in less than 12 hours.
High winds will once again batter the area too, with gusts expected to top 30mph and some reaching 50mph.
The Met Office issued a severe weather warning this morning (Sunday 12 October). It said: “Bands of rain, often heavy, and accompanied by strong northeasterly winds for a time, will affect southern and eastern parts of England through Sunday night and at times during Monday.
“The rain will clear from the south east by the morning but further heavy slow moving and potentially thundery showers are likely to occur.
“The public should be aware of the risk of localised surface water flooding.”
The warning is in force lasts until 11pm tomorrow night (Monday 13 October).
The chief forecaster said: “An area of low pressure moving north from France will bring a combination of rather persistent and sometimes heavy rainfall as well as strong winds blowing from the north east, gusting to 50 mph in places for a time.
“This combination is likely to lead to unpleasant conditions on the roads with surface water perhaps exacerbated by leaves blocking drains for example.
“The rain will clear from southeast England early on Monday morning, to be replaced by some sunshine, but also a risk of slow moving heavy thundery showers.
“10mm to 25mm of rain, starting early Sunday evening in the far south, is expected to fall widely in the warning area, with 30mm to 50mm possible over parts of southwest England and the West Country and also where showers line up into bands across east and southeast England.”