It's time to dig out that scarf and gloves as a strong cold front brings a wintry chill, blowing away Sydney's recent fortnight of relatively mild conditions.

The Bureau of Meteorology has issued a warning for gale force winds along much of the NSW coast for Wednesday and Thursday. A separate alert for cold temperatures has been issued for southern inland regions.

"Large and powerful surf conditions" are expected from Wednesday evening. These will make surfing, swimming and rock fishing hazardous until Friday, the bureau said.

"The wind chill will also be significant," Jacob Cronje, senior meteorologist at Weatherzone, said. "The evenings are going to feel very, very cold."