Chichester and Worthing will peak at 4 degrees Celsius before dropping to 1, with overcast weather forecast, the Met Office said.
Horsham will also reach 4 before dropping to zero overnight, with the district starting cloudy before changing to sunny intervals by lunchtime.
Brighton and Hastings will be overcast, reaching 4 and 5 respectively before dropping to 0 and 2 overnight.
Eastbourne will peak at 4 degrees before dropping to one 1 with light rain changing to cloudy in the afternoon.