A storm warning has been issued for Sydney this evening, with heavy rainfall on the way.
Large hailstones and damaging winds have also been forecast by the Bureau of Meteorology, with flash flooding also a possibility.
The SES has advised that people should move their car undercover and stay away from any fallen powerlines.
Locations that may be affected include Sydney, Wollongong, Gosford, Nowra, Katoomba and Dubbo.