A severe storm warning has been issued for the Sydney metropolitan area, with heavy rainfall, flash flooding and large hailstones on the way.
Locations which may be affected include Bowral, Campbelltown, Braidwood, Katoomba, Goulburn and Captains Flat.
The SES has advised people to move the car undercover and avoid flash flooding areas.
It is also a good idea to unplug computers and appliances and avoid using phones during the storm.