NSW residents have been warned to brace for yet more heavy rain, river rises, flooding and possible landslips as a stubborn east coast low threatens to bring a month of downpours in a single day.

“We know these are quite dangerous systems,” Bureau of Meteorology manager of hazard preparedness and response Jane Golding said on Friday.

“They’ve been known to produce some widespread flooding in the past, and that’s certainly on the cards for the next few days.”

Forecaster Weatherzone said some models predicted more than half a metre of rain for some areas as a huge north-west cloudband extending from the Northern Territory to NSW brings showers across a wide area of northern and eastern Australia.

“This stream of tropical moisture will interact with a broad and slow-moving upper-level trough to fuel a multiday rain event across a 3000-kilometre stretch of Australia’s east coast and adjacent inland between now and the middle of next week,” Weatherzone said.

Showers were already falling across the east coast on Friday. They are forecast to increase on Saturday, Sunday and Monday, developing into widespread areas of persistent rain.

“Certainly there’ll be a response in the rivers as a result of that rain,” Ms Golding said.

Forecast accumulated rain for the next five days from three models. Image: Weatherzone

On Friday, the wettest areas will be greater Sydney and the Illawarra region – where hundreds of millimetres of rain are forecast.

“We’re expecting some locations over the next few days, and even tomorrow, could see what they would normally see in the entire month of July all in one day,” Ms Golding said.

She said the deluge could lead to flash flooding and landslips.

“We know that the landscape is quite vulnerable at the moment and the water can move very quickly down the slopes and through the waterways,” she said.

From Saturday, flooding is possible for the Hunter, central coast, the greater Sydney region and the south coast. Flood watches are already in place for catchments between Newcastle and Batemans Bay, including Sydney and the Illawarra.

From Saturday, risk areas include Newcastle, the Central Coast, Lake Macquarie, the Upper Coxs, Colo and Macdonald rivers.

Also at risk are the the Upper and Lower Nepean and Hawkesbury rivers.

“What our hydrologists are seeing is the rain is potentially enough to cause major flooding there again, which will be the third or fourth time in the past two years for those communities,” Ms Golding said.

There are flash flooding warnings of flash flooding for the Sydney, Illawarra and Shoalhaven areas and the Cooks and Georges rivers.

Tweet from @NSWSES

The forecast for a weekend deluge comes after NSW has already been hit by repeated flooding in 2022, including two drenchings in a matter of weeks that caused devastating floods in the northern rivers region. Sydney also endured its wettest March in 80 years of records this year.

On Friday, the SES warned residents that saturated catchments were likely to produce different results when the rain fell. Commissioner Carlene York said there could be “major effects” for communities from Port Stephens to Batemans Bay.

“The accumulation of heavy rainfalls over the number of days will have a different effect on the flow of rivers,” she said.

“A different effect on flash flooding which, by its name, can come very quickly and be very unexpected.

“The main message from the SES is for people to think about their own safety and the safety of their family and friends.”

More heavy rain is also forecast for parts of central-east Queensland early next week. Weatherzone said it wasn’t expected to be as heavy as this weekend’s NSW downpours.

“However, there could still be enough rain to cause localised areas of flooding, so warnings or flood watches may be issued in the coming days,” it said.

– with AAP