Wild weather lashing Sydney and coastal NSW has led to the death of a woman, as residents are warned to brace for heavy rain and flash flooding.

An alert was issued early Sunday morning for Sydney City, Penrith and Sydney Harbour Bridge as slow-moving severe thunderstorms moved across.

It followed residents on Sydney’s Northern Beaches being warned to prepare to evacuate late Saturday at Narrabeen Lagoon and surrounds, including the BIG4 Sydney Lakeside Holiday Park.

They were advised to “prepare to evacuate before 11:30pm Saturday due to localised flooding”.

Other warnings were directed at residents at Yarramalong and Dooralong, on the central coast, which could become isolated on Sunday due to rising waters.

A severe thunderstorm warning over Sydney on Sunday morning. Photo: BOM

A slow-moving low has been hanging about offshore, dumping heavy rains and generating wild surf and strong winds along the NSW coast.

A woman died during the storms on Saturday afternoon when a tree branch fell on her car on Macquarie Pass, south of Wollongong.

“The woman was a driver in the vehicle when the incident happened,” NSW Police said.

A man in the front seat passenger suffered minor injuries, and two passengers in the rear seats were not physically harmed.

SES crews received more than 800 calls for help after heavy rain lashed NSW.

Senior meteorologist Edward Townsend-Medlock said more heavy rainfall was expected from Sydney’s northern suburbs through to the Hunter Coast on Sunday morning.

“Within that concentrated area is where you could get some of those more severe thunderstorm cells that we saw, for example, on the Central Coast,” he said.

The trough is expected to weaken by Sunday afternoon as it moves offshore.

At least 750 SES volunteers were on the ground responding to weekend storm call-outs, with the busiest units in the South Coast, Illawarra, Sydney and Hunter regions.

Almost 200 millimetres of rain fell at Moruya in the 48 hours to 9am on Saturday, with local crews responding to 30 incidents involving leaking roofs, trees down and flash flooding.

NSW SES spokeswoman Emily Barton said rain had been experienced “far and wide” across the state.

Crews would focus on the Blue Mountains, Central Coast and Sydney metropolitan area on Sunday as clean-up efforts continued, she said.

Barton encouraged people to remain alert and stay across the latest warnings and information as the severe weather weakened.

“It’s particularly important that if people are out and about and come across a flooded road, they stop and turn around and find an alternative route,” she said.

Warnings remain for hazardous surf on the east coast at beaches stretching from Newcastle to Batemans Bay, as well as the Eden coast.

Queensland also copped a bout of wild weather as a band of thunderstorms rolled across the south-east, dumping up to 60 millimetres and leaving about 11,000 properties with power.

In Victoria, sunny skies are expected on the first day of the Australian Open’s main draw.

Melbourne is set to reach a high of 29 degrees on Sunday, while Adelaide can expect a scorcher with a top of 36 degrees.

Storms and heavy rain are forecast for Darwin, with a high of 31 degrees.

Perth is set to reach 27 degrees, Brisbane 30 and Hobart 21.

-with AAP