Sydney and the Illawarra region of New South Wales have avoided the worst effects of the devastating east coast low that instead eased and shifted west over Newcastle and the Hunter region.
Newcastle remains under a severe weather warning with falls of 60 to 100mm possible over six hours and the associated risk of flash flooding.
Major flooding also remained possible at Windsor on the Hawkesbury-Nepean River, thanks to heavy rains in the surrounding catchment areas. The major flooding at North Richmond may be close to its peak, the bureau said in its most recent update on Thursday afternoon.
Authorities had to prepare for the worst as Warragamba Dam west of Sydney started spilling on Wednesday, but rainfalls were less than expected.
The gauge at the dam itself collected 237mm in the 48 hours to 9am Thursday, but just 5mm up to Thursday 3pm, Ben Domensino, a senior meteorologist at Weatherzone, said.
The east coast low developed into three separate areas of circulation just off the coast.
“That means it’s not a strong and well-defined low pressure system, and this is weakening near the coast,” Domensino said.
The Hunter will see ongoing rain, but for Sydney and the Central Coast there should only be showers. Showers near Sydney “won’t be doing too much to raise river levels”, he said.
However, there was another upper-level low pressure system crossing south-eastern Australia this weekend.
“Some models are suggesting that will cause heavier rain to redevelop from Sunday over eastern NSW and into Monday, with the potential for another low pressure system forming near the coast early next week on Monday or Tuesday.”
Earlier on Thursday, about half a million people across NSW were under evacuation orders or warnings as the wild weather that battered parts of eastern Australia for a week bore down on the greater Sydney region.
Steph Cooke, NSW’s emergency services minister, said the state had 76 evacuation orders in place on Thursday morning affecting 200,000 people, with a further 18 evacuation warnings covering about 300,000 residents.
“We have 500,000 people in our state right now who are either the subject of an evacuation warning or an evacuation,” Cooke said.
The evacuation orders covered areas of northern NSW and parts of the greater Sydney region and the Illawarra.
The Bureau of Meteorology issued multiple warnings for rivers to flood and for severe weather to affect a region of eastern NSW from near Taree, north of Newcastle, down almost to Moruya Heads on the south coast.
Flood warnings were in place for the Hawkesbury and Nepean rivers near Sydney, prompting many of the evacuations overnight, but also for the Wilsons, Richmond and Clarence rivers in northern NSW, where there have been record floods.
Warragamba Dam west of Sydney was spilling at a rate of 225 gigalitres a day with a predicted peak rate of 300-350GL a day – half the worst-case scenario.
That meant thousands of households and businesses could avoid damaging flooding from the Hawkesbury and Nepean rivers north-west of Sydney.
A cyclist rides through flood waters in Manly on Thursday. Photograph: Lee Hulsman/Getty Images
The BoM noted major flooding continued along the Hawkesbury and Lower Nepean rivers, however.
“River levels are continuing to rise at Windsor where major flooding may develop Thursday evening,” the bureau said. “Further heavy rainfall is forecast today and into Friday which may result in extended and possibly higher major flood peaks. River levels at North Richmond are expected to remain below those observed during the March 2021 event.”
The NSW State Emergency Services had received a total of 11,747 requests for help since the start of the floods crisis, with 1,462 calls coming since 3.30pm on Wednesday.
The Insurance Council of Australia said insurers have received 60,163 claims related to the ongoing flooding in south-east Queensland and NSW.
About 83% of total claims relate to property with the remainder for motor vehicles, the ICA said. “Based on previous flood events the current cost of claims is estimated to be about $900m,” the council said on Thursday.
The heavy rain and potentially damaging winds and dangerous surf were the result of an east coast low that was located about 100km east of Newcastle at 6am on Thursday.
SES personnel and police watch the rising flood water on the Hawkesbury River in Windsor on Wednesday night. Photograph: Blake Sharp-Wiggins/The Guardian
Sydney’s forecast had been revised lower to between 50mm and 90mm of rain from an earlier prediction of 100mm to 150mm on Thursday, as the low looks likely to cross the coast farther north. There remained the chance of a possibly severe thunderstorm.
Where thunderstorms form, there is the risk of locally intense rainfall, reaching as much as 200mm over six hours, leading to dangerous and life-threatening flash flooding, according to the bureau.
Many schools were closed across NSW and the SES was encouraging people in affected areas to avoid all non-essential travel.
Rainfall in the 24 hours from 9am Wednesday topped 100mm in areas of Sydney’s south, west and north-west, while the central business district collected about 50mm.
Warragamba Dam spilling, with the government on Wednesday saying the worst case could see as much as 600 gigalitres a day flow over the wall. During the March 2021 floods, the spill rate got to 440-460GL. pic.twitter.com/vnqiprJlwV — Peter Hannam (@p_hannam) March 2, 2022
The NSW deputy premier, Paul Toole, said on Wednesday the worst-case scenario was for Warragamba Dam to spill at 600GL a day. That would have been well above the 440GL to 460GL a day peak rate during the March 2021 floods.
The Warragamba spill will add to other flows coming into the Hawkesbury-Neapean River. At North Richmond, one area being evacuated, the flow is already above major flood levels. @BOM_NSW @BOM_au pic.twitter.com/26TUWigqTl — Peter Hannam (@p_hannam) March 2, 2022
The @BOM_au is forecasting the Hawkesbury-Nepean River to approach or exceed the March 2021 flood peaks. Here’s how the river looks at Windsor as its rise is starting to level off. pic.twitter.com/UGXWjcK5DM — Peter Hannam (@p_hannam) March 3, 2022
The forecast offers little solace for many along the eastern seaboard, with more rain predicted for the coming week.
And over the next eight days, still lots of rain forecast, including over areas already flood hit. @BOM_au pic.twitter.com/rhAh4i3yMh — Peter Hannam (@p_hannam) March 2, 2022
Domensino said the slow-moving system had continually exceeded forecasts for rainfall.
“This heavy rain has all been fed by an atmospheric river that’s just been dragging moisture across the Coral Sea and the Tasman Sea and directing it towards the east coast,” Domensino said. Similar big flooding events around the world have followed such patterns.
“There is a climate change signal in atmospheric rivers, and that’s been one of the components of this event.”