Motorists are being advised to slow down particularly on the A23 where there are large areas of lying water due to driving rain and winds.
A Sussex Police spokeswoman said: “There are areas of lying water and these are likely to increase during the next 48 hours when significant rainfall is forecast.
“It may only be shallow water, but hit it at even moderate speed and you can lose control of your vehicle.
“The heavy rain and winds are currently making driving conditions difficult, with low visibility, spray and water being pushed over the central reservation on the A23 by speeding motorists.
“Driver should put their lights on, slow down and drive sensibly.
“You can keep up-to-date with road conditions on our traffic and travel pages and local radio stations. Drive, cycle or walk carefully and arrive safely - even if it means your journey takes a little longer.”