St George and Sutherland Shire residents have endured an absolutely scorching day as high temperatures combined with rising humidity to make for an exceptionally uncomfortable day.
The mercury reached 37.7 degrees in the city at 1pm in line with the Bureau of Meteorology's forecast top of 38 degrees for Sydney.
Temperatures have since dropped back.
Wednesday marks the fifth day the city has passed 35 degrees this summer, the most since the summer of 1990-91, according to Weatherzone.
A weak change is expected to arrive in the city about 5pm, but "not before temperatures will be absolutely scorching in Sydney", Jacob Cronje, a senior meteorologist with Weatherzone said.
So far, the hottest site in the basin has been Badgerys Creek, which touched 41.7 degrees at 1.16pm.
For places such as Bankstown and Homebush, it was their hottest day in four years with 41 degrees reached, said Brett Dutschke, also a senior meteorologist with Weatherzone.
Stormy conditions could arrive at about the time of the change or soon after, Mr Dutschke said.
"Western suburbs are more likely to see them than eastern suburbs," he said, adding they could be severe, with strong, gusty winds.
Fire authorities have been on a high alert throughout the day, with total fire bans declared in five regions in the state, including the greater Sydney and Hunter regions.
Many shire residents made an early beeline for the beach on Wednesday after enduring a sweltering summer's night, with temperatures staying above 20.
After another very mild night with temperatures expected to remain in the low 20s, Sydney will get a bit a breather, heat-wise, with only 27 degrees predicted by the bureau for Thursday.
The heat will return, though, with 33 forecast for the city on Friday, although the mercury may head higher to the mid-30s, Mr Cronje said.
- This story first appeared in the Sydney Morning Herald