A developing low is expected to bring heavy falls and dangerous winds from Nowra through to Batemans Bay on Saturday night, the Bureau of Meteorology says.
Six-hourly rainfall totals of between 80 and 120mm are predicted, with strong to damaging winds of between 50 and 70km/h, and 90km/h gusts.
Areas at risk include Batemans Bay, Huskisson and Ulladulla.
Conditions are expected to ease on Sunday afternoon.
The NSW State Emergency Service has urged people to keep track of weather updates, prepare their homes and avoid driving if possible.
"Localised flash flooding could result in roads being closed at short notice. Please do not take the risk and find an alternate route if you need to travel," SES Assistant Commissioner Nicole Hogan said.
"Landslips are also possible, and I would urge the public to remain vigilant."
SES units are ready in the area to respond to calls for help overnight, the emergency service said.
"While the NSW SES is well prepared for heightened levels of operations, it is critically important for people to take responsibility and be prepared," Ms Hogan said.
People should tie down any loose items on their properties, park their cars undercover and away from trees, and trim branches that could fall and cause damage.
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