Sydney's grey clouds and drizzle are just a preview of wild weather expected tomorrow, forecasters say.
Winds of up to 100 km/h are forecast for the coast in the Illawarra and further south tonight, the BoM said.
The severe weather is predicted to hit Sydney tomorrow, Weatherzone meteorologist Rob Sharpe said.
"There's a low pressure system that's just forming and moving out to sea and it will swing back in tomorrow and come close to the coast.
"That will bring strong to gale force winds in the Sydney area tomorrow. It will also bring heavy rain as well."
Today, Sydneysiders can expect some showers, Mr Sharpe said.
"Once this morning rain clears it will tend to shower and be on and off today.
"Tomorrow there's potential for quite heavy falls in Sydney and along the coast."
The severe weather will also continue to hit the Illawarra and south coast tomorrow.
"The NSW coast up to the Hunter is going to experience potentially severe weather tomorrow," Mr Sharpe said.
The NSW State Emergency Service advised people to move their cars away from trees and secure loose items around the yard.
The SES also warned people not to drive, walk or ride through flood water and to stay away from power lines, and flooded creeks and drains.
South of the city, a severe weather warning for damaging winds, heavy rain and damaging surf has been issued by the Bureau of Meteorology for the Illawarra, south coast, southern tablelands and Snowy Mountains later today.
"Gale force, damaging winds are expected with this system, particularly along the coast, and localised heavy rain may cause flash flooding," the warning said.
Snow is also forecast for Perisher Valley, Cabramurra and Thredbo.