Chichester will be sunny, with highs of 22 degrees Celcius and lows of 15, the Met Office said.
Worthing starts cloudy changing to sunny by late morning with a high of 23 and a low of 16.
Horsham will see sunny intervals, highs of 22 and lows of 15.
Brighton and Hastings will start with sunny intervals changing to partly cloudy by nighttime. They will have highs of 22 and 20 respectively before dropping to 15 overnight.
Eastbourne starts sunny changing to cloudy by nighttime, highs of 20, lows of 15.