Environment

Sydney braces for another potential thunderstorm

The greater Sydney region is bracing for another possible thunderstorm on Friday, after strong winds and hail hammered south and south-west suburbs on Thursday, bringing down trees, damaging roofs and cutting power to thousands of residents.

Penrith and Campbelltown were hard-hit as large hail and wind gusts of up to 117 km/h damaged properties, Bureau of Meteorology forecaster Jane Golding said.

More thunderstorms set for NSW

Heavy downpours are forecast for areas north of Sydney Friday, with the weekend bringing more stable and cooler conditions. Meteorologist Josh Fisher reports.

Thousands of homes and businesses on the Ausgrid network in Loftus, Yarrawarrah and parts of Balgowlah were left without power for several hours on Thursday.

The State Emergency Service had 215 requests for assistance, SES spokesman Todd Burns said. Most of the calls involved toppled trees, and leaking and damaged roofs mainly caused by fallen trees, he said, adding that SES crews would be working on 50 outstanding jobs this morning.

But the clean-up could be hampered by the possibility of further storms developing this afternoon, Ms Golding said.

"The air mass when they come through is not so different from yesterday so there could be a storm like that somewhere in Sydney or the greater Sydney area," she said.

"It's more likely outside Sydney, but there's still a chance [for the storm to happen] within Sydney in the afternoon period."

Ms Golding said that at this stage, the storms were most likely to hit the mid north-coast and the north of Sydney this afternoon.

Thursday's wild weather was caused by humidity and an inflow of moisture from the tropics into NSW, which has combined with systems coming through from the south and caused "unstable conditions", she said.

But Sydney is expected to enjoy a storm-free weekend as a front coming through from the south brings dry air into the region and pushes the moisture towards the north-east, Ms Golding added.