The Bureau of Meteorology has issued a severe thunderstorm warning for the Illawarra, South Coast and Southern Highlands.
The warning was issued just after 4pm on Sunday, with damaging winds predicted for several hours.
Locations which could be affected include Wollongong, Nowra, Bowral, Bulli, Port Kembla, Albion Park, Kiama and Huskisson.
Residents should move cars under cover or away from trees, secure or put away loose items around the house, yard and balcony, keep at least eight metres away from fallen power lines or objects that may be energised, such as fences and unplug computers and appliances.
Fallen power lines should be reported to Ausgrid on 131 388; Endeavour Energy on 131 003, or Essential Energy on 132 080.
For emergency help in floods and storms, ring the SES on 132 500.