Fog might have hidden the sun in Sydney on Thursday morning, but a top of 24 degrees will bring an above-average stint of July heat before the city returns to winter as normal over the weekend.

Early on Thursday, all Sydney Ferries were cancelled due to the heavy fog, with the Manly to Circular Quay service replaced by a bus. However by 8.10am all services had resumed, and the fog had largely cleared by 9am.

The fog also caused delays at Sydney Airport with low visibility procedures put in place, but those delays were expected to ease by mid-morning.

Weatherzone meteorologist Brett Dutschke said the sun did a good job of burning off the fog, helped by north-westerly winds coming from the interior and bringing in warmer air.

"Today looks like being the most pleasant of the coming days, not too windy but windy enough to get the washing dry," he said.