It was a sweaty start to the morning for Sydney residents with higher than usual overnight temperatures.
At 11am on Wednesday Kurnell had reached 26 degrees while at Mascot it was 31.
Weatherzone senior meteorologist Brett Dutschke said it was unusually hot for early spring.
"It will warm up very quickly," he said.
"The winds will freshen early leading to a dry, dusty day with a fair bit of pollen blowing around.’’
The city is forecast to come close to challenging its warmest day this early in September on record, with the Bureau of Meteorology expecting the mercury to climb to 32 degrees.
That's about 12 degrees above the average for September. Inland suburbs will be similarly warm after places such as Richmond topped 30 degrees on Tuesday.
Sydney has only had one day of 32 degrees or warmer in the first half of September, and that was a 32.2-degree reading on 13 September, 2009, Blair Trewin, senior climatologist at the bureau, said.
The NSW Rural Fire Service said total fire bans will be in place for the Greater Sydney, Greater Hunter, north coast and north-west region of the state.
Crews from the RFS and Fire & Rescue NSW will be ready to respond to any new outbreaks should they occur, including calling in aircraft assistance.
The total fire ban, the first for the 2017-18 season, will probably last one day in the Sydney region but places further north may have restrictions for a couple of days, Ben Shepherd, an RFS spokesman, said.
"For those fires that were contained in the past few days, obviously we'll be monitoring them closely," Inspector Shepherd said, adding that any unintended fires "should be reported immediately".
The unusually early fire bans come after NSW posted its driest winter in 15 years with about half the usual rainfall. Fire authorities earlier this month predicted an early and active bushfire season for most of east coast Australia.
A 30-degree day on Wednesday would be about four weeks earlier than the first such day in 2016.
Predicted wind strengths were another reason for the total fire ban declaration, Inspector Shepherd said.
The winds "start to build in the afternoon, carrying through to Thursday morning," Lachlan Maher, a meteorologist with Weatherzone, said.
A front will cross the state, drawing in warm air from central Australia ahead of it.
"Once the front passes, it'll just be a slow cool overnight into Thursday," Mr Maher said.
Recent conditions have been pretty dry across NSW which "would certainly help increase the intensity of fires", he said.
Weatherzone is owned by Fairfax Media, publisher of this website.
with Rachel Browne and AAP