SES volunteers have responded to more than 200 calls and conducted seven rescues on NSW's south coast, after areas flooded only last week receive another drenching.
The Bureau of Meteorology has issued flood warnings for St Georges Basin and the Bega River, with flood watches also issued for the Shoalhaven, Deua and Moruya areas from Saturday.
Sussex Inlet is expected to approach minor flooding levels around 11pm, while the Bega River is forecast to hit minor flooding levels from 3am.
Nowra has copped the heaviest rain so far, with over 200mm falling in the past 24 hours - almost its monthly total for July.
Continuous heavy rain is forecast until Monday, with the low-pressure system causing the havoc also bringing strong winds to suburbs still reeling from recent wild weather.
The State Emergency Service is urging residents in affected areas to stay out of floodwaters, and be ready to evacuate if needed.
Four of the seven rescues already conducted were people in vehicles swept away by floodwaters.
SES spokesman Andrew McCullough said it's disappointing that volunteers are called to these types of rescues time and time again.
"We urge people to find another way that does not require driving through floodwaters, because even a small amount of floodwater can wash a vehicle off the road and end in tragedy," he told AAP on Saturday.
NSW BOM's flood manager Justin Robinson said this weekend's flooding is likely to be even worse than last week.
Heavier rainfall is expected, and the catchment is already soaked so will absorb less of it.
Flash flooding is already occurring across the region, but Mr Robinson said the worst of it is expected to begin on Saturday night.
"Obviously if you get some very, very heavy localised rainfall you will see some flash flooding, which obviously impact your streets, your houses, and local drains," he told reporters on Saturday.
"But once that floodwater then reaches the rivers, we'll then see those major riverine floods, which is really the ones that we're concerned about."
Conditions are expected to ease by Monday.
Disaster assistance has been made available to those impacted in the local government areas of Bega Valley, Eurobodalla, Kiama, Shellharbour, Shoalhaven and Newcastle.
Big waves are also forecast right up to the Central Coast from Sunday, and heavy snowfall is expected in the alpine regions.
Australian Associated Press