Sydney is in for a soggy few days as a complex system steers moist air over the coast, with the possibility of heavy falls further north up the coast over the long weekend.

The city has collected another 61 millimetres since 9am on Wednesday. Added to the 54 mm recorded in the previous day, Sydney's two-day rainfall total is the most since last June's huge east coast low lashed NSW.

Bureau of Meteorology figures show that among the wettest places to Thursday morning included Little Bay, which had received 56 mm and Chatswood 52 mm, matching similar falls at those sites for the day.

Passengers on Wednesday night experienced significant delays at Sydney Airport after a storm knocked out a number of radio frequencies, cutting some communication between planes and the control tower. Flight schedules had returned to normal by Thursday morning.