The county is set to start off cloudy before brightening up later in the day.
Chichester will have sunny intervals by lunchtime, peaking at 13 degrees Celsius before dropping to eight overnight.
The rest of the county will be sunny by lunchtime.
Worthing, Horsham and Brighton will peak at 12 degrees before dropping to a low of eight overnight.
Hastings and Eastbourne will reach 11 degrees before hitting a low of nine overnight.