Extreme unseasonal weather is expected across NSW tomorrow, prompting fire authorities to issue "extreme fire danger" warnings.
The Illawarra is forecast to reach 37 degrees - 15 above the long-term average - and other areas may climb to 40, with winds gusting as high as 70 kilometres per hour in some regions.
"These conditions mean there is potential for the rapid spread of fire," Shane Fitzsimmons, Rural Fire Service Commissioner, said.
The warning, one level before the "catastrophic" level, applies to the Illawarra, Greater Sydney, Greater Hunter and Shoalhaven regions.
A total fire ban is expected to be set for Thursday.
With little rain since mid-June and the three-month outlook pointing to warmer and drier than average conditions, much of NSW is now primed for a tough fire season.
As of late yesterday, the state had 37 fires burning, 10 of them yet to be contained.
None of those 10 blazes are in the regions expecting extreme fire danger conditions tomorrow, an RFS spokesman said.
The abnormally warm weather is similar to recent bursts, said Blair Trewin, senior climatologist at the Bureau of Meteorology.