The county will start the day cloudy before brightening up later in the day.
Chichester will see heavy rain by nighttime with a peak temperature of 12 degrees Celsius and a low of nine, the Met Office said.
Worthing will see sunny intervals in the afternoon with a high of 12 and a low of ten.
Horsham is forecast to have sunny intervals by lunchtime peaking at 13 degrees before dropping to a low of ten overnight.
Brighton will also be sunny this afternoon, reaching a high of 12 before dropping to nine.
Hastings and Eastbourne will have sunny intervals by lunchtime peaking at 12 degrees before dropping to nine overnight.