Authorities said on Saturday afternoon it could take some time for the dangerous conditions to subside, with the “worst yet to come”.
The NSW State Emergency Service (SES) will send emergency alert text messages tonight to communities along Hawkesbury-Nepean watersheds, if evacuations become necessary.
The SES said low-lying Hawkesbury-Nepean communities will receive warnings that they could be hit by flooding on Saturday or the following days, depending on rainfall distribution.
Areas expected to receive warnings tonight include Menangle, Liverpool, Milperra, Camden, North Richmond, Wallacia, Penrith, Sackville, Upper Colo and Windsor.
“If you receive a text from +61 444 444 444, it is an official warning that requires attention and action must be taken early,” the SES said, asking people not to think it’s a scam and to ignore the message.
“If you’ve had flooding in the past, you could be hit again.
“Municipalities can now prepare by understanding their risks and monitoring weather conditions.
“Protect yourself, property and livestock by acting early and avoiding flooded roads. If you need to arrange accommodation with family and friends, prepare now.
“If you had vacations booked, stay away from flood-prone areas and plan your travels carefully.”
The downpour currently stretches from Port Stevens in the north to Batemans Bay in the south and everything in between.
Emergency Services and Resilience Minister Steph Cooke said residents in affected areas should remain vigilant as the outrageous conditions are expected to worsen during the evening.
“My message to everyone today is if you haven’t been hit by rainfall yet, don’t think you’ve been spared,” Cooke said.
“Maybe we haven’t seen the worst yet.
“There is a very real threat of a low east coast developing into Sunday.
“This can lead to torrential rains, flash flooding, damaging winds and coastal erosion, making our coastline and our cities very dangerous places to be.”
Cooke said that given the “already record rains” the state has experienced this year, the soil is still saturated.
“Our entire landscape, in fact almost directly across from NSW, is saturated at the moment,” Cooke said.
“And of course our dams and river channels are full too.”
Meanwhile, Queensland will see up to 25 millimeters of rain over the weekend before conditions temporarily ease.
The weather system can pick up again on Monday with even more wet weather.
Flash flooding and river flooding are “very real” risks in the coming days.
Cooke said: “This could happen anywhere from Newcastle to Jervis Bay”, with the river system “of the greatest concern” at the Hawkesbury-Nepean.
“It can reach a major flood level overnight,” she said.
Authorities have also expressed concern about the Warragamba Dam, which could see significant leakage in the coming days.
As of 4pm this afternoon, the Upper Nepean, Avon and Cordeaux Dams have reported a spill.
“We’re all nervously waiting to see what happens,” Cooke said.
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Helicopters, unimogs and other resources are placed to ensure they can respond quickly in an emergency.
Cooke urged residents to keep an eye on watches, warnings and orders from the Bureau of Meteorology, the SES and other emergency services in the coming days.
“Please be ready to evacuate at short notice,” she said.
“Be sure to prepare your belongings as best you can, prepare your families and pets if necessary, and if in doubt, evacuate early.
“Don’t necessarily wait for us to place an order, ask, or propose to leave.”