Another storm cell was moving south-easterly from Berowra over Hornsby and was expected to reach the Northern Beaches and Mona Vale by 5.30pm. A previous storm affecting Sydney's north passed Mosman at around 5pm.

"It's quite a large cell," said Steph Spackman of the Bureau of Meteorology. "Again, we are looking at damaging winds, large hail and possible rainfall."

Thunderstorms moving in a south-easterly direction were hitting Sydney's northern suburbs on Saturday afternoon.

"There have been really strong steering winds pushing the storm in, quit deep easterly winds have stretch it out all the way to the coast in some form," said BoM meteorologist Jordan Notara. "Although we haven't seen reports large hailstones on Sydney's coastal fringe."

Hail has been reported in Sydney's north-west with golf ball-sized chunks falling in Rouse Hill, Castle Hill, Londonderry and Kellyville. There have also been reports of hailstones further east in Hornsby.

#sydneyhailstorm Hornsby @nampix for @smh pic.twitter.com/64xjYi1F2T— Nick Moir (@nampix) February 18, 2017

Currently, the Bureau of Meteorology is tracking another storm cell that has formed north-west of Sydney that is moving towards Wisemans Ferry, as well as multiple storms moving south-easterly towards the central coast and Newcastle.

"We are currently not tracking any more storm cells in the southern parts of Sydney," Mr Notara said.

At 3.15pm a severe storm was detected at Bowral, which has now passed. Three sisters in their sixties were hit by lightning while they were sitting together on a bench in Corbett Gardens.

Two of the women have been treated for shock, and one woman is expected to be airlifted to Sydney to be treated for severe burns.

Following the significant damage caused by Friday's severe weather, about 8000 homes and businesses were still without power on Saturday morning, the majority of which were on central coast, a spokeswoman for Ausgrid said.

Pockets of Palm Beach and Avalon would likely be without power until Sunday, while small numbers of residences and businesses on the central coast would have to wait until Monday to turn on the lights.

Sunday is expected to be mostly dry and overcast, except for possible showers and storms in Sydney's north.

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