Steph Spackman from the Bureau of Meteorology (BoM) said north-westerly winds were crossing the Sydney basin and bringing warm air from further inland.

Temperatures are expected to drop to about 16 degrees in the city at 9pm, and Sunday morning will see a chilly start with minimum temperatures of about 10 degrees between 5am and 6am.

Loading

"This sort of weather isn't unusual for this time of the year but it certainly does feel a lot cooler when you do get those larger drops," she said.

While Sydney dealt with the soaring mercury on Saturday, other parts of the state were being buffeted by wild winds and dust storms.

Authorities issued an emergency warning for residents living near Bemboka on the South Coast after an out-of-control bushfire, which has been burning for several weeks, ramped up due to strong winds blowing embers ahead.

Severe weather warnings for damaging winds were also issued for other communities in the Illawarra, South Coast, Snowy Mountains and parts of Southern Tablelands, South West Slopes and ACT.

The gusty, dry conditions prompted the NSW Rural Fire Service to increase the fire danger threat level for the Sydney Metropolitan region to "severe", triggering a total fire ban.

"We had a gust at Thredbo recorded earlier today of 105km/h, and Ulladulla had a gust of 94km/h, so it is a bit windy out there today," Ms Spackman said.

"The warm dry and gusty air, has significantly increased the fire ratings today."

Thirty-degree days this early in spring are becoming more common.

Loading

Four of the 10 years in which the mercury has reached 30 degrees before or on September 15 occurred in 2008, 2009, 2013 and last year.

On Sunday, Sydney is expected to be sunny but only reach 17 degrees.

"Winds southwesterly 25 to 35 km/h decreasing to 15 to 25 km/h in the middle of the day then becoming light in the evening," the BoM's forecast said.

With Cassandra Morgan