"We're bracing for significant rainfall right across NSW today," Flood Recovery Minister Steph Cooke said on Friday.
A broad risk of showers and thunderstorms is menacing much of NSW on Friday and will continue into the weekend, Jonathan How from the Bureau of Meteorology said on Friday.
A severe thunderstorm warning is in place for parts of the Mid North Coast on Friday, with a risk of flash flooding in Coffs Harbour, Kempsey, Woolgoolga, Sawtell, Dorrigo and Macksville.
A second severe warning is also in place to the west, on the North West Slopes, Plains and Upper West, with a risk of flash flooding, large hailstones and damaging winds in Moree, Narrabri, Mungindi, Burren Junction, Boggabri and Collarenebri on Friday.
On Saturday and Sunday, rain and storms will continue in the east, with heavier falls likely in the northeast, depending on the development of a low-pressure system, Mr How said.
"These systems may produce heavy rain on Saturday and into Sunday and could impact highly populated areas including the Sunshine Coast, Brisbane, the Gold Coast in Queensland, and in the Northern Rivers in NSW," Mr How said.
Lismore and Byron Bay are of particular concern to the bureau over the weekend, he added.
While the systems are expected to ease into the middle of next week, flood impacts will be ongoing, with roads and infrastructure likely to be affected.
Some 15 flood warnings have been issued across the state, with emergency services keeping a watchful eye on the Gwydir, Namoi and Upper Macintyre rivers on Friday, after heavy rainfall on Thursday led to renewed river rises across the inland catchments.
Flood mitigation efforts are continuing in Moama, the sister town to Victoria's Echuca, which has been the focus of the flood threat in recent days.
The Murray River passed major flood levels late on Wednesday night and is now within 20 centimetres of the 94.77m height of a 1993 flood, the area's second-worst on record.
The bureau expects the Murray to reach around 95m next week, still below the 96.2m height of its worst flood in 1870.
Hundreds of people have been ordered to evacuate Moama and surrounds this week.
"We are very much on high alert," Ms Cooke said.
"Communities have been battered over and over again by natural disasters, particularly since the 2019/20 bushfire season."
Ms Cooke made the comments before opening a temporary housing village in the Northern Rivers town of Coraki, which is providing homes to 240 residents left homeless by flooding in Lismore and surrounds earlier this year.
Meanwhile, western Sydney residents are expecting minor to major flooding to begin on the rising Hawkesbury-Nepean rivers on Friday.
Several suburbs including Windsor, Penrith, and North Richmond have been told to monitor the conditions.
The Hawkesbury-Nepean region has already suffered two major floods this year.
The threat of flooding comes as the NSW government presses the federal government to share funding for the proposed $1.6 billion raising of the Warragamba Dam on a tributary of the Nepean River.
"This is an important project for the protection of property and lives in western Sydney," NSW Premier Dominic Perrottet told 2GB on Friday.
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