Already saturated, NSW is bracing for significant rain that could lead to flash flooding on the state's south coast.
The Bureau of Meteorology has issued a severe weather warning for localised heavy rain overnight Saturday and on Sunday that could cause flash flooding in the Illawarra region.
A strengthening onshore flow in the area would worsen the rain from early morning Sunday until late evening, the bureau said, with predicted six-hourly falls of up to 140mm.
Isolated falls of more than 150mm were also possible.
Affected locations were expected to include Wollongong, Bulli, Port Kembla, Albion Park and Kiama.
A moderate flood warning was also in place for the Warrego River.
The bureau cancelled previous warnings for the Hunter, Central Coast and Greater Sydney.
Senior meteorologist Angus Hines earlier told AAP rainfall could lead to flooding as the east coast was already saturated after a dumping in April.
"This is significant rainfall that could lead to flooding, perhaps localised flooding, certainly blocking terrain, closed roads and traffic jams," he said.
Floodwater reached the top of cars in some areas of the Illawarra and Sydney a month ago.
"So we're not expecting to see the same type of flood response, but it's enough rain that we will probably see some areas of localised flooding and Illawarra is again in the firing line," Mr Hines said.
A hazardous surf warning continues from the Illawarra Coast to the Byron Coast, contracting to the Byron Coast on Sunday.
The Sydney Half Marathon was set to go ahead on Sunday with more than 19,500 runners registered.
The NSW State Emergency Service was closely monitoring forecasts with all flood rescue personnel rostered on for any potential issues.
SES Zone Commander Allison Flaxman said the agency was focusing on flash flooding where roads could be cut off.
"We don't need much rain to cause a flash flood scenario ... it only takes 15 centimetres of water across a road to actually move a car," she said.
