They don't play the Triple J Hottest 100 on Australia Day anymore, but in Sydney and elsewhere in southeast Australia, it's going to be plenty hot with or without the tunes.

The harbour city is bracing for an absolute scorcher on January 26, with a maximum of 35 degrees forecast for the city, and 41°C in parts of the city's west. Temperatures in the eastern half of the city will feel all the more oppressive due to humidity.

In 162 years of records dating back to 1859, Sydney’s "official" weather station at Observatory Hill, just beside the Harbour Bridge, has recorded just five days of 35 degrees or higher on January 26, with the hottest being 1960, when the mercury reached 41.1°C.

But the classic beer and barbie weather is rarer than you might think.

Image: Our national day is an important time to reflect on who we are as a nation, or perhaps just whether you want BBQ or tomato sauce. Source: Pixabay.

In Melbourne, hotter Australia Days tends to be much more common. The Victorian capital has peaked at 39 degrees or higher six times on January 26, in records dating back to 1856. It has also reached 35°C 22 times.

This year, the scorching weather is coming a day early to Melbourne, with a top of 39°C forecast for Monday after a Sunday night when temps barely dipped below 30°C across much of the city.

Conditions should cool significantly on Tuesday, with 22 degrees and rain forecast. BBQs on covered back porches is our strong recommendation.

Image: You can clearly see the hot airflow being directed towards Sydney on the 10 pm Monday synoptic chart, while a trough and cooler weather approaches Melbourne.

"A hot airmass is spreading over southeast Australia ahead of an approaching low pressure trough," Weatherzone meteorologist Ben Domensino explains.

"This is the same heatwave that caused fires in South Australia on Sunday, and today it's spreading through Victoria and into NSW. Tomorrow the heat and fire danger will be focused in NSW – especially around Sydney."

Whatever you're doing on Australia Day, stay cool. And if, like this reporter, you have a cricket match on, maybe come off the shorter run when bowling, and when batting, try to hit boundaries rather than running quick singles, twos and threes!