UPDATE:
Sydney's temperature peaked at 37.8 degrees just before 2pm, and had eased back to 34 degrees by 4pm. A gusty cool change is on the way but will not arrive in the city until about 5pm after stalling earlier this afternoon, Tristan Meyers, a meteorologist from Weatherzone, said.
Earlier: Many of Sydney's commuters had a sweltering journey to work today, but it's likely to be much hotter on the journey home as temperatures soar towards the high 30s ahead of a late cool change.
Sydney had its warmest November night in four years, with the temperature this side of midnight dipping to 23.5 degrees before bouncing back.
By just after 8.30am, the mercury had already reached 31.6 degrees on the way to a forecast top of 38 degrees.
40 [degrees] is a very outside chance," Brett Dutschke, a senior meteorologist with Weatherzone, said.
It's likely that there will only be weak sea breezes through the day, with Bondi's expected top of 36 degrees not far behind the maximums expected of about 38 degrees across the Sydney Basin.
A strong southerly change will probably arrive in the city's southern suburbs by about 4pm and could take as long as two hours to reach north-western parts of Sydney, Mr Dutschke said.
While the change may not be as strong as last Friday's - after Sydney's top reached 40.9 degrees - it is likely to be bringing wind gusts of 70-80km/h, Mr Dutschke said.
Fire dangers will be severe for much of the region, the bureau said in a fire warning alert.
Total fire bans are in place for the Greater Sydney, Greater Hunter, northern slopes and north-western regions of NSW, the Rural Fire Service said.
There is only a small chance of a shower with the change, Mr Dutschke said.
Adding to the day's torments, pollen levels are likely to be extreme today for hayfever sufferers, Weatherzone said.
