State Emergency Service chief superintendent Sonya Oyston said people should be tying down loose items, parking cars under cover or away from trees and cutting branches on properties that may cause damage.
"With already saturated soils, it will not take much for these damaging wind gusts to easily pull out trees and damage your property," she said.
The Bureau of Meteorology is forecasting 90 km/h winds across parts of the state from Sunday night into Monday, including in Bowral, Braidwood, Bathurst, Katoomba, Goulburn and Cooma.
The bureau is also expecting peak gusts of 125 km/h in NSW's higher alpine areas.
With the storms come cold conditions and graziers across the South West Slopes, Snowy Mountains and ACT are being warned the weather could be deadly for lambs.
Rain and thunderstorms are forecast to hit Sydney from Monday morning before skies clear again on Tuesday and Wednesday.
The SES said flood operations were continuing in western and southern NSW with towns still cut off by waters.
Chief Supt Oyston said people needed to stay vigilant despite the current calm conditions.
"Despite blue skies and a reprieve in rainfall, due to saturated soils and full catchments, flooding conditions can change quickly with future rainfall," she said.
There are 46 flood warnings in place across NSW including two emergency warnings.
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