If you woke to the sound of thunder early this morning be prepared for it to continue throughout the day.

Forecasters predict heavy rain, strong winds and increasing swells.

Sydney is in for another wet and windy day on Friday as the clean-up continues after destructive storms tore through the city, felling large trees and powerlines, crushing cars and cutting power to thousands of homes on Thursday afternoon.

A "strangely warm southerly" is sweeping across Sydney today with little relief from the heat at beaches in NSW and Queensland because of Cyclone Winston causing large, dangerous and powerful surf.

Parts of Canberra have received more than the city's June average rainfall in less than two days with more rain on the way.