If this April in Sydney often felt more like mid-summer than mid-autumn, you wouldn't be far off the mark. And there's more out-of-season warmth to come.

Even before the final temperatures for the month settle on Monday, readings for the first 29 days are far enough ahead of previous records to make it certain that April will be Sydney's hottest in almost 160 years of records, Weatherzone says.

"It was a really, really hot month," Kim Westcott, a meteorologist with Weatherzone, said.

Temperatures in Sydney this April have been more typical of those in mid-summer. Credit:Janie Barrett

"Certainly, it's not isolated to just Sydney and NSW," she said, adding that South Australia and Victoria were also likely to challenge historical records.