Between 80mm to 120mm of steady rainfall is forecast for Batemans Bay and Narooma on Monday, while Sydney and Wollongong could receive more than 35mm on Tuesday.

"The good news is the catchments are dry (on the South Coast) so they need quite a lot of rain for any riverine flooding," the Bureau of Meteorology's Jane Golding told reporters on Sunday.

"It doesn't quite look like at this point that we'll be getting anything more than minor flooding."

The low-pressure system behind it could still potentially develop into an official East Coast Low but will be weaker than previous modelling had suggested.

"It looks like the low is going to develop a bit further off the coast than the ones that bring the flooding rains we sometimes see in those systems," Ms Golding said.

Some rain will fall as snow on the eastern Alps but little will make it over the ranges.

The focus for Tuesday is now the severity of the winds predicted, and how they will whip up coastal waters.

Based on modelling from Sunday morning, Ms Golding said there would likely be gale-force winds in some coastal areas as far north as the Hunter.

"The waves do look like they'll be pretty big - more than five metres in open waters to the east," she said.

"It's certainly not a day to be out boating and one to take care if you're in the surf zone."

People along the coast have been urged to prepare their properties and watch for updates and warnings.

The lack of vegetation and numerous dead wildlife on the NSW South Coast due to recent bushfires complicated issues during heavy rainfall in February.

While there has been more growth and building in the intervening months, the SES said it's "still a matter of concern".

"We're aware it's been a pretty difficult year on the South Coast," SES spokeswoman Stephanie Heard told AAP on Sunday.

"This is why we're taking the opportunity to prepare these communities and making sure they're getting their properties ready.

Ms Heard urged locals to heed emergency services' advice to stay out of and never drive through flooded roads.

"Don't take the risk," she said.

Australian Associated Press