The forecast sweltering heat started early with the mercury speeding past 20C early in the day.
A heatwave expected to last until Wednesday across most of southern Australia saw Canberra reach 33C shortly after 2.30pm, while Sydney and Melbourne peaked at 28C and 27C respectively, which was slightly lower than predicted for those cities.
Adelaide sweated through 38C heat in the late afternoon and Perth residents saw a top of 25C about lunchtime.
The high heat in Western Australia has prompted total fire bans across parts of the state, with firefighters already battling bushfires over December.
The minor heatwave brought temperatures of 27C or above to most state and territory capitals on Monday, giving Australians an excuse to put their feet up and munch on Christmas Day leftovers.
Melburnians had excellent conditions for a dip, or a trip to the MCG where Australia faced South Africa in the Boxing Day Test.
The Northern Territory was warned of further flooding on Boxing Day with ex-tropical cyclone Ellie bringing rain to parts of the Top End's interior.
That weather system is slowly moving through the Barkly district which includes Tennant Creek, Elliott, Ali Curung, Ampilatwatja, Barrow Creek and Renner Springs.
Ex-cyclone Ellie could also bring heavy rainfall for part of western Queensland, which may cause localised flash flooding in the Diamantina and Georgina rivers, Eyre Creek and part of the Simpson Desert.
To the south, communities along the Murray in South Australia are keeping watch with the river expected to have peaked in Renmark and due to peak downstream at Mannum in about two weeks.
Flood levees have been holding amid the deluge, but people in the Bolto shack area were told to shelter in place after damage to a road cut them off on Christmas Day.
The Bureau of Meteorology also has a number of flood warnings in place for parts of NSW and Victoria along the Murray River and its tributaries.
Heavy fog caused travel headaches in Sydney earlier on Monday with flights into the NSW capital delayed and the city's ferry service temporarily halted.
34°C