Those humid northeasterly winds would bring gusts up to 80km/h along the NSW coast from late afternoon on Friday to Saturday morning, Hernandez said.
While the worst of the weather is expected on Friday, the Bureau of Meteorology is forecasting thunderstorms to form over the north-east of the state from Thursday, bringing rain to Sydney by the afternoon.
The NSW State Emergency Service (SES) has issued 34 warnings for locations across NSW, mainly for possible flooding. It is advising people around Sydney, Parramatta, Gosford, Wollongong, Nowra, Bowral, Batemans Bay, Katoomba and Goulburn to “prepare now” for damaging winds and heavy to locally intense rainfall.
The SES has responded to more than 317 incidents across NSW since the start of the weather event, including four flood rescues. Flood rescue teams have been positioned across the state ahead of the anticipated intense rainfall.
“We’re anticipating significant rainfall which may lead to dangerous and life-threatening flash flooding across Sydney, the Hunter, Blue Mountains, Illawarra and South Coast from tomorrow,” Assistant Commissioner Kearns said.
Warragamba Dam, which supplies much of Sydney’s drinking water, is expected to reach capacity over the next few days. It is currently 96 per cent full.
“The upper end of the forecast would result in the dam experiencing a more significant spill,” Water NSW said.
The Bureau on Thursday issued a hazardous surf warning for large tracts of the NSW coast.
The convergence of the two weather systems is a recipe for wild weather as warmer ocean temperatures this time of year cause more evaporation, increasing the amount of water in the atmosphere.
When this moisture is carried south by humid north-easterly winds and cooled by the colder air in the upper-level low-pressure system above, it condenses and falls as rain.
Catchments likely to be affected by flooding include:
- Tweed and Rous Rivers (minor flooding)
- Richmond River (minor flooding)
- Orara River (minor flooding)
- Coffs Coast
- Bellinger and Kalang Rivers (minor flooding)
- Nambucca River (minor flooding)
- Hastings River (minor flooding)
- Camden Haven River (minor flooding)
- Manning and Gloucester Rivers (minor flooding)
- Wallis Lake (minor flooding)
- Myall River (minor flooding)
- Karuah River
- Goulburn and Upper Hunter Rivers (minor flooding)
- Wollombi Brook and Lower Hunter River (minor to moderate flooding)
- Newcastle Area
- Paterson and Williams Rivers (minor flooding)
- Central Coast
- Lake Macquarie (minor flooding)
- Upper Nepean River (minor to major flooding)
- Hawkesbury and Lower Nepean Rivers (minor to major flooding)
- Upper Coxs River
- Colo River (moderate to major flooding)
- Macdonald River
- Northern Sydney
- Southern Sydney
- Parramatta River
- Cooks River (minor flooding)
- Georges and Woronora Rivers (minor to moderate flooding)
- Illawarra Coast
- Shoalhaven River (minor flooding)
- St Georges Basin (minor flooding)
- Clyde River
- Moruya and Deua Rivers (minor flooding)
- Tuross River
- Bega River (minor flooding)
- Towamba River
- Upper Macintyre River (minor flooding)
- Gwydir River (minor flooding)
- Macquarie River to Bathurst (minor to moderate flooding)
- Orange, Molong and Bell River (minor to moderate flooding)
- Lachlan River to Cotton’s Weir (minor flooding)
- Belubula River (minor to moderate flooding)
- Mandagery Creek (minor flooding)
- Queanbeyan and Molonglo Rivers (minor flooding)
The phenomenon was seen repeatedly throughout Sydney’s wettest year on record in 2022, which brought widespread flooding across the state.
The “Black Nor’easter” is a different system to the one that dumped a month’s worth of rain on Victoria in less than 24 hours earlier in the week, Hernandez said, but would bring more rain and wild weather to the state on Saturday and Sunday.
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A woman almost drowned in a stormwater drain as Victorian emergency services responded to hundreds of calls for help during the wild weather.
It also caused carnage on the sporting calendar as the Stawell Gift was delayed due to a waterlogged track, and the AFL’s lightning policy forced Geelong and Hawthorn players to abandon the MCG turf for more than an hour during their Easter Monday clash.
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