Forecasters are warning there's a high risk of widespread flooding as multiple weather systems move across NSW and days of heavy rain fall on already saturated catchments.
A succession of three rainfall systems will bring downpours across large tracts of the country's east this week, with parts of the state's inland regions already hit with showers and thunderstorms.
"This rainfall is likely to lead to widespread flooding across many of our rivers across NSW," Dean Narramore from the Bureau of Meteorology said on Tuesday.
"It will be a difficult week but even more so a difficult summer and significant flooding is expected," Premier Dominic Perrottet told reporters on Wednesday.
"Our rivers and dams are full, that creates a significant risk of flooding that creates a risk to people's lives and properties," he said.
"There will be many challenges as we move through this period of time, but our focus is a government is to save lives, protect property, and our SES volunteers do an amazing job," Mr Perrottet said.
SES crews were working to prepare communities near swollen rivers and dams for the onslaught of rain to come later in the week, the premier said.
He urged people to avoid risks and follow SES instructions.
'Significant amounts of rain'
Assistant SES commissioner Sean Kearns says he's very concerned about western and southwestern parts of the state as more rain falls on drenched catchments.
"This is going to impact communities that have already been impacted by floods over the last month or two," he told ABC TV on Wednesday.
"What we're going to see is significant amounts of rain, sometimes the monthly rainfall in just a couple of days, if not more."
There are particular concerns around the areas of Gunnedah, Wee Waa, Warren, Bathurst, Forbes, Gundagai, Tumut and Wagga Wagga.
The school holidays means there are a lot of people travelling in areas they may not be familiar with.
"So really take heed of conditions, be very mindful about caravan parks and camping grounds, they're often next to rivers," he said.
Mr Kearns also warned racegoers heading to Mount Panorama for the Bathurst 1000 race this weekend to take heed of the conditions and follow SES directions amid concerns the Macquarie River could be hit with moderate to major flooding.
Floodwaters west of Condong near the town of Murwillumbah, NSW, Friday, September 23, 2022. Source: AAP / JASON O’BRIEN/AAPIMAGE
Heavy falls and thunderstorms with a risk of flash flooding are expected in the western parts of the Riverina and Central West Slopes and Plains on Wednesday as a trough drags moisture across inland NSW.
A severe warning for heavy rainfall covers a large part of the state's west, from Nyngan in the central north to Deniliquin near the Victorian border through to Broken Hill in the central west.
Inland towns on flood watch include Deniliquin, Griffith, Hay, Tibooburra, Cobar, Bourke, Broken Hill, Wentworth and Brewarrina.
Widespread six-hourly rainfall totals of 30-40mm are expected, with some localised falls of up to 60mm.
The bureau expects 50-70mm of rain will collect in the gauges over a 24-hour period, with some areas copping 100mm.
Hazardous surf and swell are expected on the Macquarie, Hunter, Sydney, Illawarra, Batemans and Eden coasts on Wednesday.
A second trough will bring storms, rain and bursts of heavy falls from Queensland to southern Victoria from Thursday night and into Friday.
Finally, a third rainfall system will sweep across southern Queensland, NSW and eastern Victoria on Saturday and Sunday.
Flood warnings are current across numerous inland catchments including the Namoi, Macquarie, Bogan, Lachlan, Murrumbidgee, Murray, Edward, Culgoa, Birrie, Bokhara, Warrego, Paroo, Barwon, Darling and Snowy rivers.
A flood watch has also been issued for minor to moderate flooding for rivers closer to the coast, including the Hunter, Hawkesbury and Colo rivers, and Wollombi Brook, with rises expected over the weekend.
Warragamba Dam wall rise now 'critical'
It comes as the $1 billion-plus proposal to raise the Warragamba Dam wall has been declared critical state infrastructure, opening up the project to fast-track development.
Mr Perrottet announced the decision to pursue the project on Wednesday as NSW faced a repeat of widespread flooding, with a month's worth of rain predicted to fall on saturated catchments in the coming days.
"Today is a landmark day ... for a project that has been talked about for decades," he told reporters.
The NSW government has committed to raise Sydney's Warragamba Dam wall, with the premier saying it will save lives and properties.
Mr Perrottet stressed he didn't want the vital infrastructure bogged down in red tape and government bureaucracy, saying "we need to prepare, we need to invest".
"It is all about saving lives and protecting property," he said, adding the project was necessary to help protect western Sydney from floods.
