The county is set to start off sunny before turning cloudy later in the day.
Chichester, Hastings and Brighton will peak at 18 degrees Celsius before dropping to 11, 13 and 12 degrees respectively overnight, the Met Office said.
Worthing and Eastbourne will peak at 19 before dropping to 12 degrees and Horsham will be slightly cooler, peaking at 17 degrees before dropping to 11 overnight.
