Weather warnings are already in place for wind and rain, with the Met Office predicting heavy rain and coastal gusts of up to 65mph from today (October 2).
Up to 100mm of rain is forecast to fall in some areas, bringing a risk of flooding.
Despite the grave predictions, the Met Office forecast for Sussex also predicts a slight calming of the weather in the middle of today, with heavy cloud potentially even giving way to sunny spells. Temperatures are expected to reach a maximum of 16 degrees Celsius.
The rain will pick up again into the evening, coming in from the east and turning heavier at times, with the wind forecast to crank up into the night.
Temperatures are expected to drop to a minimum of 11 degrees Celsius.
The gloomy weather is predicted to persist through Saturday and Sunday.
Jonathan Day, Flood Duty Manager at the Environment Agency, said: “Heavy rain will bring the potential for surface water flooding and perhaps some river flooding across the south of England on Friday. More widespread and persistent heavy rain across much of England will bring the potential for further river and surface water flooding over the weekend.
“Environment Agency teams have been working hard to clear grills and weed screens in areas which may be affected, and are ready to support local authorities leading on responses to surface water flooding incidents, should they occur. We urge people to stay away from swollen rivers and not to drive though flood water – it is often deeper than it looks and just 30cm of flowing water is enough to float your car.
“You can check your flood risk, sign up for free flood warnings and keep up to date with the latest situation at https://www.gov.uk/check-flood-risk, call Floodline on 0345 988 1188 or follow @EnvAgency on Twitter for the latest flood updates.”