Torrential downpours could push daily rainfall totals as high as 200 to 250 millimetres in the Illawarra this week.
Subscribe now for unlimited access.
$0/
(min cost $0)
or signup to continue reading
Bureau of Meteorology senior hydrologist Ailsa Schofield said a coastal trough developing would bring widespread falls of 50 millimetres on Wednesday, from the Upper Hunter down to the South Coast.
"We're really expecting to then see this trough intensify on Thursday, where we're expecting to see between 50 to 150 millimetres of rain in these same central and southern coastal areas of NSW," Ms Schofield said.
She said similar rainfall was expected on Friday, but it would ease over the weekend.
"I should highlight within this widespread rainfall, there is the potential for isolated heavier totals," Ms Schofield said.
"So for Wednesday we might see higher rainfall totals in excess of 100 millimetres, on Thursday we may see rainfall totals in excess of 200 to 250 millimetres, and then again on Friday we may see higher rainfall totals in excess of 150 millimetres."
The BoM has issued an initial flood watch, warning of possible minor flooding on the Shoalhaven River and St Georges Basin.
Ms Schofield said the forecast heavy rain also brought the potential for flash flooding in the Illawarra.
"The catchments are very wet and it won't take very much rainfall for us to see flash flooding or river rises," she said.
"We therefore expect potentially dangerous road conditions and the potential for further landslips."
NSW State Emergency Service assistant commissioner Dean Storey said the SES and other agencies were preparing for the weather event, sending resources to the areas of higher risk.
"We're really urging the community to be aware of your local risks, continue to monitor your local forecast and warnings," Mr Storey said.
"Things can change quickly, so remain vigilant."
He also urged people to have plans in place in case they were affected by flooding.
Mr Storey said people should also avoid unnecessary travel and never drive through floodwaters.
"Time and again, SES and other emergency services need to respond to people who have made poor safety decisions by choosing to drive through floodwaters, and putting themselves, their families and emergency service responders at unnecessary risk," he said.
"So if it's flooded, forget it, turn around and find another way."
The Northern Rivers region - already devastated twice over by flooding in the space of five weeks - could see more rain but the heavy falls are expected to hit further south.
People are advised to keep up-to-date with the Bureau of Meteorology warnings and the advice of authorities like the SES.
Mr Storey said people should keep an eye on local SES unit social media pages for information on sandbag collection points and other support.
Those in need of emergency assistance can call the SES 131 500. If someone's life is at risk, call triple-0.
The Illawarra Mercury newsroom is funded by our readers. You can subscribe to support our journalism here.
Sign up for breaking news emails below...