The Illawarra is set to sizzle today, with temperatures forecast to reach 30 degrees.
The prediction comes after the region's warmest night on record for the period.
Weatherzone meteorologist Brett Dutschke said temperatures hovered between 22 and 23 degrees all night and were expected to soar to 30 degrees as early as 11am.
"The [Sydney] airport will probably be first place to reach 30 [and the] inner city most likely early afternoon."
Sydneysiders woke to balmy weather, with the mercury rising to 25 degrees at Sydney Airport by 6.45am and 23 degrees in the city.
"This is a sign that the day is going to be very warm and warm up fairly quickly," Mr Deutschke said.
The summer-like heat has been brought by north-westerly winds from central Australia and will be felt from the Illawarra to the Hunter regions.
"The winds that are driving this warmth are north-westerlies and they will comfortably bump the temperatures to 30 degrees, even at the beaches."
The temperature began to rise from 10pm on Monday night and reached 20 degrees across Sydney by midnight.
But with the heat and wind comes a day of extreme pollen levels and a high risk of fire danger.
"It's been really dry for the last month or two across Sydney [and] we are likely to see fire danger ratings reach the severe category."
The Rural Fire Service said there was a very high fire risk across Sydney, the Illawarra and the Hunter.
The NSW Rural Fire Service said this means all fire permits are suspended.
Residents that have been issued a permit cannot burn until the very high fire danger period has passed.
Mr Deutschke said he expected temperature to rise above the official forecast of 29 degrees in the city and 30 degrees at Penrith and Richmond.
"[It will be] about 30 degrees right across Sydney. I anticipate that temperatures will go a little above the official forecast."
Over the past 150 years or so of records, days of 30 degrees or warmer are not that common in Sydney with only a 40 per cent chance that any September will have one.
The likelihood, though, is increasing as Australia's temperatures creep up. The record of 30-degree days in September is three and that tally has happened in four years. Three of those years were in 2006, 2008 and 2009, with the fourth in 1907, according to Acacia Pepler, a climatologist at the Bureau of Meteorology.
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