Chichester will start cloudy changing to sunny intervals in the afternoon, the Met Office said. Temperatures will peak at 16 degrees Celsius, dropping to 11 overnight.
Horsham starts off cloudy changing to light showers by lunchtime, highs of 15 and lows of 10.
Worthing will start with heavy rain changing to cloudy in the afternoon with a high of 15 and a low of 12.
Hastings starts with light rain changing to cloudy by lunchtime, highs of 15, lows of 13.
Eastbourne and Brighton will see light rain changing to overcast by lunchtime, highs of 15, lows of 13.