Christmas Day barbecues are expected to take place under grey skies after a cool change rolled across eastern NSW following scorching temperatures on Christmas Eve.
Sydney's observatory hill reached 37.7 degrees Celsius just after 2pm on Sunday but it was well shy of Penrith's 42.1C maximum.
Penrith came close to breaking a record set just ten days ago when it reached 43.5C.
A thunderstorm and cool change helped drop temperatures from mid-afternoon and Christmas Day is expected to reach a maximum of 23C in the city and 26C in the west.
The state is expected to see a gradual warming after Boxing Day and, potentially, another cool change on New Year's Eve.
Victoria
Break out the ugly holiday-themed jumpers for festive barbecues in Melbourne - it's set to be a rather cool Christmas Day.
The city is predicted to hit a top of 22 degrees Celsius, with a chance of drizzle and mild winds before the sun comes out in the afternoon.
The cooler forecast is set to be repeated across the south of the state, with Gippsland towns likely to hit 21C in the east and Warrnambool set to hit the same temperature in the west.
North of Melbourne the barbecues will see more traditional Christmas weather, with Wodonga and Wangaratta reaching 31C and Shepparton 30C.
The heat is expected to return to Melbourne on Tuesday, in time for the expected large crowds at the Boxing Day Test, with the city set to hit 29C.
Western Australia
Perth is expected to enjoy a sunny 32 degrees on Christmas Day, while other parts of the state are predicted to have temperatures hovering in the low to mid 40s.
Coastal areas in the state's southern half are expected to experience similar weather to Perth, such as Esperance and Bunbury, while Albany is likely to be a cooler 26 degrees.
The Bureau of Meteorology predicts Marble Bar will be the hottest place in WA, with the mercury tipped to reach 44 degrees.
The temperature is expected to hover in the 40s through the inland Pilbara region in the state's north. Some rain is also possible.
A tropical cyclone may also form in northern WA later in the week.
Queensland
Queensland looks set to sizzle on Christmas Day, with temperatures tipped to reach 45 degrees Celsius in some parts.
Bureau of Meteorology forecaster James Thompson said a top of 34 was expected in Brisbane, compared to 32 on the Sunshine Coast and 31 on the Gold Coast.
"It looks like it'll probably be pretty close to the warmest day for December this year across the southeast," he told AAP on Sunday.
Mr Thompson said a sea breeze would likely be felt across Brisbane in the afternoon.
There is also the slight chance of a late storm, but Mr Thompson said the likelihood was higher further south and inland.
The BoM on Sunday said severe thunderstorms were likely south of the Gold Coast and down to the NSW border.
South Australia
Last year’s extreme heat will be a memory this year as South Australia's southern parts gear up for mild weather in the mid-20s on Christmas Day.
Temperature of 25C are expected in Adelaide.
The Bureau of Meteorology said warmer weather would be felt in the state's north.
“Adelaide goes from about 29C on the Sunday but cools down to 25C on the Monday, so it’s looking pretty good on Christmas Day,” senior forecaster Vince Rowlands told the Adelaide Advertiser.
“But we will see some hotter temperatures in the north. Anywhere above Port Augusta will be warmer, with Woomera predicted to be 43C.”
