Sussex has been put on alert with heavy rain expected to sweep across the county tonight and tomorrow morning.

Forecasters warn up to 20mm of rain could fall, leading to localised flooding in some areas as drains struggle to cope.

It comes after Sussex experienced one of its wettest Aprils on record, with about 100ml of rain hitting the county.

An Environment Agency spokesman said: “We have no concern about river flooding but there might be some standing or surface water. Environment Agency field teams will be out in the area to check that grilles are clear.”

Ian Michaelwaite, from Horsham-based forecasters Netweather, said: “There is going to be a lot of rain quite hard over a relatively short period of time and this could overwhelm the drains and potentially affect roads.

“It looks as though it could be bad during the rush-hour in particular so people will need to take care.

“The better news is that is seems the weather could start to improve by the end of the week and temperatures in the second half of the month should be rising.”

The Met Office has issued a yellow weather alert for the county, warning people to be aware of potential problems.

The average rainfall for May is about 58mm but Sussex has already experienced almost half of that so far.

Mr Michaelwaite said: “If we get the large amount we are expecting then we are probably going to pass the usual monthly rainfall for May before we’re even halfway through.”

The heavy rain is expected to have an impact on sea water quality along the coasts as it could wash raw sewage from overflow pipes and pollution from towns and rural areas into bathing spots.

The bad weather had an impact on events around the county over the bank holiday weekend, although it did not stop thousands of people going out and braving the rain. They included almost 12,000 visitors to the South of England Centre in Ardingly, near Haywards Heath, on Sunday and Monday for the annual spring garden and leisure show.

Despite the weather, the hosepipe ban is not likely to be lifted because groundwater supplies will only be replenished by large and consistent amounts of steady rain for up to two months.