An east-coast low has brought heavy rainfall to an already saturated Sydney catchment, leading to major floods on the Hawkesbury, Nepean, and Colo rivers.
"Conditions are likely to worsen before they get better," said Andrew Edmunds, a spokesperson for the New South Wales State Emergency Service (NSW SES).
Floods are likely to exceed some flood levels reached in the three recent major Hawkesbury flood events since March 2021.
Driving the expected flood peaks was another burst of heavy rainfall overnight.
"As the low approaches, we're seeing increasing rain late tonight, early into tomorrow morning, " said forecaster Jonathan How from the Bureau of Meteorology on Sunday.
"We are warning for the potential of six-hourly rainfall totals of up to 120 millimetres."
Heavy falls may also hit parts of the Illawarra, inland from Wollongong, which have already seen more than 600mm of rain since Friday.
That is almost half of Sydney's average annual rainfall in just two days.
Damaging winds, surf on the way
However, flooding is not the only hazard the Sydney region is facing, according the Bureau of Meteorology.
"We'll also see some damaging winds tonight," Mr How said.
"We're already seeing some pretty strong winds developing along the Sydney coasts of around 70 to 80 kilometres an hour.
"As that low pressure system moves towards the coast, we'll see a ramping up of the winds."
A damaging surf warning is also in place, with waves around five metres coinciding with high tides tonight, leading to beach erosion.
Rain is expected to ease on Tuesday, however the floodwaters may remain high.
"New South Wales, you've been through this before. It's unfortunate it's happening all over again," Mr How said.
Dam spilling faster than 2021 floods
The overnight downpour led to Sydney's main dam, Warragamba, spilling hours earlier than predicted, according to Tony Webber, a spokesperson for dam operator WaterNSW.
"The storage has reached capacity and exceeded capacity at 2am this morning, well ahead of expectations, due to the intensity of the rain in the catchment," he said.
By yesterday afternoon, water was spilling from the dam at a faster rate than at the peak of the major floods of 2021, according to WaterNSW.
Mr How said saturated soils were compounding the intense rain, accelerating the rate of river rise.
The Hawkesbury River at North Richmond was forecast to reach around 15 metres late Sunday evening, with major flooding.
The Bureau of Meteorology says further rises are possible with the forecast rainfall.
Andrew Edmunds from NSW SES said 41 evacuation orders and 44 warnings had been issued to communities in the Illawarra, Western Sydney, and the Hawkesbury-Nepean areas.
The SES advises those subject to flood warnings to be prepared to leave.
"Have your emergency kit ready to go with warm clothes, important documents, medications, laptops, phones, and chargers," Mr Edmonds said.
"And make sure you try and keep up to date as best you can overnight on the SES website and Facebook pages and also the Bureau of Meteorology website."
