December is warm or hot almost everywhere in Australia in December. Tasmania experiences the coolest temperatures, with average December highs in Hobart of 68° F (20° C). However, it would be a mistake to assume that cities in the south are always cooler than those in the north. Adelaide, Melbourne, Canberra, and Sydney can experience heat waves in December (and throughout the summer) with temperatures in excess of 105° F (40° C). The average temperatures aren't that high, though. Average December highs in Adelaide, Canberra, and Sydney are 79° F (26° C), and in Melbourne 77° F (25° C). Perth, despite being on roughly the same latitude as Sydney (but on the opposite coast) is hotter, with average highs around the same as Brisbane, 84° F (29° C). In short, you can expect hot weather in Australia in December, wherever you go.
With the exception of the tropical north (northern Western Australia, northern Northern Territory, and northern Queensland), December is also quite a dry month in most places. Brisbane can be a bit wet in December as it experiences most of its rain in summer and autumn, and is also very humid in summer. Other cities don't get much rain in December at all.
Conditions are pretty hot in the desert in December: Alice Springs has average highs of 95° F (35° C), and overnight lows of 68° F (20° C).
Crowds and Costs
December is low season in the tropical north, which experiences high temperatures and heavy rain between November and April, but high season everywhere else.
Many Australians take at least a week's vacation around Christmas and New Year, and schools are out for several weeks over December and January. Expect to see a lot of domestic tourists around the country, or at least locals getting out and about and enjoying their local attractions, particularly later in the month.
Accommodation and transport will be busy later in December, especially in popular places, so book these as far in advance as you can to avoid disappointment or the need to pay inflated prices. But, as Australia is an enormous country, even in December you will be able to find quiet places, if that's what you're seeking.
Where to Go
Unless high humidity, tropical rain, and temperatures of around 95° F (35° C) are up your street, avoid the tropical north in December. Even if you did venture to these places under these conditions, you wouldn't be able to swim in the sea (as many travelers like to do in the tropics) because of the presence of deadly jellyfish at this time of year.
Other than that, practically everywhere else in Australia is accessible in December. The southern cities can get hot, but they're also full of air-conditioned indoor spaces, and have beautiful beaches nearby. Although the outback can get very hot, you can fly into Alice Springs and/or Uluru to avoid driving in scorching conditions. Tasmania remains cooler than most of mainland Australia (although it also experiences heat waves and bush fires), and is an outdoor lover's paradise.
What to Do
To enjoy hiking in the mountains in cooler temperatures, Tasmania should be on your radar. As mentioned above, it's usually cooler than mainland Australia, and a large proportion of the island is comprised of forested, mountainous national park or preserve.
Many travelers to Australia like to swim in the sea or spend time at the beach, and there's no shortage of options for this in December. You don't need to travel far from the main cities in the south, as all of them (except for inland Canberra) have excellent city beaches nearby. For more remote beach adventures, head to southern Western Australia, the long coastline between Sydney and Brisbane, or the south coast of New South Wales.
Christmas and New Year. Many events are held throughout Australia in the run-up to Christmas, and in the week between Christmas and New Year. Wherever you go, something will be on to celebrate the festive season. Sydney is an especially lively place to spend New Year's Eve.
Cricket matches. Sporting enthusiasts are likely to find cricket matches throughout the country in December.
Sydney to Hobart Yacht Race. This important yacht race starts on 26th December, and can be seen from Sydney Harbour.
Traveling to Australia in December? Check out these great itineraries
Gold Coast and Byron Bay - 7 Days. Enjoy the sun, surf, and sand on this week-long tour of Australia's famous Gold Coast and Byron Bay.
Melbourne to Great Ocean Road: Self-Drive Tour - 5 Days. On this five-day, self-drive trip, explore the coastal capital city of Melbourne and then hit the open road. One of Victoria's most scenic drives, Great Ocean Road provides plenty of exciting pit stops