By the first weekend, many populated regions will have copped temperatures close to or above 40 degrees as a pulse of heat sweeps across southern Australia. Melbourne can expect 39 degrees on Saturday while parts of western Sydney may reach 40 and 44 degrees on Saturday and Sunday, respectively.
The longer-term forecast, though, is for a relatively damp start to the year. The latest Bureau of Meteorology climate outlook for the first three months of 2018 show the odds favour more rain than usual for almost all of the country. (See chart below).
"The cloud and the rain reduces the chance of getting searing heat," Brett Dutschke, a senior meteorologist with Weatherzone, said.
Mr Dutschke said sea-surface temperatures were "still fairly high" - particularly off south-eastern Australia - creating conditions for above-average rain.
Still, the warm end to 2017 - likely to be among Australia's five warmest years in records that go back to 1910 - means any relative easing in temperatures may barely be noticeable for many regions.
La Nina events typically mean eastern Australia turns wetter and cooler than usual, as a strengthening of easterly winds along the equatorial Pacific drags more rain westwards.
The La Nina, though, is expected to be weak and end by autumn, the bureau predicts.
Break in the weather: summer may turn cooler and wetter than average. Photo: Jason South
Heat in places
The south-eastern corner of the nation, though, can get hotter than usual weather during La Ninas, and the next few months look like following that pattern.
A region spanning west of Adelaide and taking in eastern Victoria and Tasmania can expect above-average daytime temperatures over the January-March period, particularly during January, the bureau said.
While heavy rains drenched eastern Victoria in early December, areas to the west of a line roughly running from Melbourne north to Echuca on the Murray mostly missed out, said Craig Lapsley, Victoria's emergency management commissioner.
"We move back into really hot weather again" in the first week of January, he said.
Places of most concern for fire authorities in Victoria include Warburton, Healesville and the Otways. These areas near Melbourne swell with holiday visitors.
Tarps cover damage done by giant hailstones after a storm in February 2017 over Sydney's Rouse Hill. Photo: Nick Moir
NSW fire threat
For NSW, recent soaking rains and storms have eased the fire threat, especially in the state's north-east.
Still, the 100-odd fires that were started by lightning just prior to Christmas showed risks remain high for many parts of the state, said Ben Shepherd, senior spokesman for the NSW Rural Fire Service.
Inspector Shepherd said the dry winter and spring of 2017 had left much of NSW with unusually dry fuel loads.
According to the Keetch-Byram Drought Index used by the RFS, a region stretching from Nowra on the south coast up to Sydney and through the Hunter Valley remains particularly dry. (See chart below.)
Areas in Sydney's north and west, such as Terrey Hills and Richmond, have soil moisture readings worse than in 2002-03, a summer of major fires. (See below.)
"It probably needs 80-100 millimetres of rain to bring conditions back to where they would normally sit for this time of year," Inspector Shepherd said.
Also watching the skies closely over the coming months will be governments wary of blackouts if the electricity sector fails to cope with surging demand for cooling.
Last summer, South Australia suffered outages and NSW came close during a February heatwave.
This year, the network supplying eastern Australia is lacking Victoria's Hazelwood power station after its closure last March, while another ailing plant, AGL's Liddell in the Hunter Valley, will be down one of its four 420-megawatt units possibly until February.
With Victoria's Hazelwood power station closed, power supplies could be strained again this summer. Photo: Joe Armao
Another threat may come with cyclones, although the worst of the impacts are typically restricted to the less-populated north of the country.
La Nina years typically have an above average number of cyclones crossing the Australian coast.
So far, this summer has had a relatively quiet start to the cyclone season, as did the 2016-17 year.
In fact, the whole southern hemisphere has been seen relatively few cyclones, with record low levels since accurate records began with the satellite era about four decades ago, according to Philip Klotzbach, a research scientist in the Department of Atmospheric Science at Colorado State University.
Southern Hemisphere Accumulated Cyclone Energy (ACE) is only 8% of normal for the 2017/18 season to date - the lowest Southern Hemisphere ACE on record from July 1 through December 29. pic.twitter.com/vbIYjByn1R??? Philip Klotzbach (@philklotzbach) December 30, 2017
"There are no strong signs of a particularly cyclony season" for Australia, Mr Dutschke said.
Weatherzone is owned by Fairfax Media, publisher of this website.
The story Kicking off 2018 with a heatwave, and then cooler, damp conditions will set in first appeared on The Sydney Morning Herald.