A looming heatwave in early 2018 is unlikely to augur an exceptionally hot year for Australia as a weak La Nina in the Pacific will start to tilt the odds to relatively cool and wet conditions for much of the nation, forecasters say.

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.

Surfers pick up a nice swell at Dee Why. Credit:Nick Moir

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.