Heavy rainfall, large hailstones and damaging winds are coming for Sydney and surrounding areas, as well as the Northern Rivers, the Bureau of Meteorology (BoM) said on Sunday.
Residents are being warned to prepare for severe thunderstorms, which could lead to flash floods in some areas.
It comes as a wet “unstable air mass, supported by an upper trough” moves across the eastern parts of NSW.
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People in metropolitan Sydney, the Illawarra, Central Tablelands and parts of Northern Rivers, Hunter, South Coast, Southern Tablelands, Central West Slopes and Plains and South West Slopes have all been issued safety advice.
Areas that may be affected by the floods and hail include Sydney, Wollongong, Nowra, Orange, Goulburn and Dubbo, and in the Northern Rivers, Murwillumbah, Mullumbimby, Byron Bay, Ballina, Alstonville and Brunswick Heads are all likely to be affected, BoM said.
Cars should be moved under cover or away from trees, loose items around properties should be secured, and computers and appliances should be unplugged where possible, the State Emergency Service (SES) warned.
“Trees that have been damaged by fire are likely to be more unstable and more likely to fall,” it said.
The SES also shared safety advice relating to the dangers of power lines in a storm.
”Keep at least 8m away from fallen power lines or objects that may be energised, such as fences,” it said.
Fallen power lines can be reported to either Ausgrid (131 388), Endeavour Energy (131 003), Essential Energy (132 080) or Evoenergy (131 093) “as shown on your power bill”, SES said.
It also urged people in the affected areas to avoid storm water.
“Keep clear of creeks and storm drains,” SES said. “Don’t walk, ride your bike or drive through flood water.”
For emergency help in floods and storms, ring the SES (NSW and ACT) on 132 500.
Meteorologists will issue an update on the BoM website at 5pm.