Fog patches are expected to lead to some travel disruption.
A Met Office statement read: "Impaired visibility leading to hazardous driving conditions in places, and probable slower journey times especially by road; Delays to bus and train services are possible
"There is a chance of delays or cancellations to flights
"Not everywhere will see fog patches, but where they do occur they may be dense with visibilities dropping to between 50 and 100 metres in a few spots.
"Conditions should slowly improve on Saturday, although a few areas of fog may last until afternoon across the east of the warning area."
Looking at the full weather forecast, it has been a cold and frosty start to the day across Sussex. It will remain cloudy through the afternoon but it could be bright and sunny later in western areas. Temperatures will peak at six degrees Celsius.
Temperatures will drop to minus one tonight but will become milder by dawn.
A cloudy morning is expected tomorrow (Sunday), with some light rain possible by early afternoon.
It will be breezy near coastal areas and turn sunny during the afternoon. There will be highs of nine degrees Celsius.