"The north-westerly and westerly winds should be strong enough to hold out any sea breeze," Kim Westcott, a meteorologist with Weatherzone, said.

Days of 30 degrees this early in spring are fairly uncommon in Sydney but are becoming less so.

At Observatory Hill, only nine years have posted such readings by September 15 since records began in 1858. Of those, four have come since 2008, according to Blair Trewin, senior climatologist with the bureau.

The warmth won't linger, though, with the cold front likely to produce a "drastic drop" in temperatures when it rolls across Sydney from the south-west by late afternoon to early evening, Craig McIntosh, a Weatherzone meteorologist, said.

The mercury should drop rapidly to as low as 17 degrees in a couple of hours, buffeting spectators at the NRL's knock-out final at Homebush's ANZ Stadium. "You could have a game that starts off quite warm and ends quite chilly," Ms Westcott said.

Fire concerns

The change, though, will bring little rain for farmers and fire crews anxious about the state's ongoing drought.

Wind gusts in the Sydney region could reach 65 km/h, while those in the Hunter up to 75 km/h. South-east parts of the coast - including near Bega where a fire is already burning - could see gusts up to 80 km/h.

The Total Fire Bans, which come into force at midnight, are based on "how strong the winds are, and how dry the landscape is", Ben Shepherd, a senior RFS spokesman, said.

As of Friday afternoon, there were 13 bush, grass and shrub fires in NSW, eight of which were yet to be contained, Inspector Shepherd said.

Surf and snow

Sunday's forecast top in Sydney will drop sharply to 17 degrees - much like the water temperature for those brave enough to take a dip at the city's beaches.

Conditions for outdoor activity will likely improve at the state's alpine resorts, where strong winds and rain on Saturday should make way for fresh falls on the higher peaks on Sunday, Mr McIntosh said.

Snow depths have been in retreat at places such as Spencers Creek for the past couple of week, according to Snowy Hydro.