Melbourne has endured its warmest night in almost five years but relief is arriving for the country's southeast.
A cool change crossed Victoria on Wednesday having already brought rainfall to Adelaide, where temperatures plummeted 16C in six hours.
The front also brought a sprinkling to Melbourne, where temperatures fell 5C in 14 minutes before dipping below 20C about noon.
It followed an oppressive night where the mercury sat above 30C at midnight and only slid to 27.1C moments before dawn.
Tuesday was the hottest day of 2022 for Melbourne (37.4C), Horsham (39.4C) and Ballarat (34.9C).
The cold front was expected to also ease the heat in Hobart on Wednesday afternoon after temperatures reached 29C by 9am.
Maximum temperatures are expected to hover around average or below average on Thursday and Friday, before warming up again into the weekend.
Elevated areas of Victoria and Tasmania could also see potentially damaging winds of up to 90km/h ahead of the change, expected to ease by Wednesday afternoon.
A severe wind warning has been issued for the central and eastern ranges in Victoria, including the Grampians and Otways, and for southern, central and eastern districts of Tasmania.
Inland NSW towns could reach 40C on Wednesday before the cool change, which should reach Sydney on Wednesday night.
Sydney's outer west should reach 35C but the city looks likely to notch up its first year without a day above 32C.
Warnings are also in place for parts of the Northern Territory's Barkly district where ex-Tropical Cyclone Ellie is dumping heavy localised rainfalls bringing flash flooding.
The system is expected to track close to Tennant Creek on Wednesday before moving northwest and intensifying in the Gregory district and Kimberley region of Western Australia later in the week.
Yachts arriving in Tasmania for the Sydney Hobart are expected to see winds swing from northerly overnight to southwesterly early on Wednesday afternoon, along with the slight chance of a shower.
Temperatures are tipped to warm up again over southeast Australia into New Year's Eve, becoming warm to hot for the long weekend.
Early forecasts for New Year's Eve night and New Year's Day:
Sydney 19C - 26C. Partly cloudy.
Melbourne 19C - 34C. Humid. Mostly sunny.
Brisbane 19C - 30C. Partly cloudy. Shower possible, less likely in the evening.
Perth 15C - 32C. Sunny.
Adelaide 16C - 32C. Sunny.
Hobart 16C - 27C. Partly cloudy. Slight chance of showers.
Canberra 13C - 27C. Partly cloudy. Slight chance of evening thunderstorm
Darwin 25C - 30C. Showers. Storm.
