The intense heat that's been plaguing Adelaide and Melbourne is heading Sydney's way, but things are going to be a lot stickier in NSW.
Heatwave conditions are expected to peak on Australia Day, with parts of the city's west forecast to reach 43C and a more bearable 34C in the CBD.
Areas in the state's west were already sizzling on Friday, with Hay, Swan Hill, Ivanhoe and White Cliffs all surpassing 46C by lunchtime.
A high pressure system over the Tasman Sea that's barely moving and a trough across inland NSW have allowed heat and humidity to build up over NSW, while heat is also being pushed south from central Australia.
"The combination of the heat and humidity makes it quite sticky, muggy and gross - particularly if you're in the eastern parts of NSW," the Bureau of Meteorology's Gabrielle Woodhouse told reporters in Sydney on Friday.
Thunderstorms are possible throughout the state on Saturday and Sunday, but they're expected to bring little rain.
Temperatures are tipped to drop only slightly by Monday before the heat returns.
"Whilst this change is going to cool a little bit, it's going to be very short-lived," Ms Woodhouse said.
Sleeping isn't going to be easy over the next few nights either, with minimum temperatures to remain above 20-25C in Sydney and higher in the state's west.
"It's going to be quite difficult to recover from the heat that we'll see during the day," Ms Woodhouse said.
Health authorities are again warning people to stay hydrated and minimise physical activity - particularly the most vulnerable, including the elderly, children, and those with heart and lung conditions.
While many take to the outdoors on Australia Day, NSW Health's Richard Broome suggests staying out of the sun especially in the afternoon.
"Perhaps think about having a breakfast BBQ rather than an afternoon BBQ, or even postpone your activities until after it gets dark," he told reporters.
"We understand people do like to enjoy a beer, but please do it in moderation."