Sydneysiders have endured the hottest November night since 1967, the mercury not dipping south of 25.3C.

And the extreme heat will continue throughout Sunday with sky high temperatures predicted from the CBD to Penrith.

Respite is still hours away, a gusty southerly not expected to bring the cool until this afternoon.

"Last night's minimum went down to 25.3 degrees at Observatory Hill," meteorologist Helen Kirkup told NCA NewsWire.

"Previously the highest November night on temperature was 24.8 degrees, which was in 1967."

For Sunday, she said, the prediction is: "Just hot. Really hot."

The warm north-westerly wind will stick around and likely see the CBD hit 40C and Penrith 42C.

A cool southerly is expected to blow in between 2pm and 5pm, making for a far more comfortable evening.

Northeastern NSW is also facing a sweltering day, with Grafton expected to hit 42C and Taree 41C.

"If you drew a line from Dubbo across to Tibooburra, everything above that is likely to get well over 40 today," Ms Kirkup said.

The southern part of NSW, in particular the Riverina, suffered yesterday but is not expected to get as hot today.

"Along the Victorian border we're looking at high 20s, low 30s, and that's because that wind change will come through this morning," Ms Kirkup said.

Saturday saw extraordinary temperatures across Australia.

Marree in South Australia hit a deeply uncomfortable 47.5C, Queensland's Birdsville 46.4C and Fowlers Gap in NSW was 46.2C.

Originally published as Heatwave to bring temps as high as 42C