With just a day's data to be collected, the average of maximum and minimum temperatures for the month was 29.7 degrees. That tally was 1.79 degrees above the long-term average.

Short of a remarkably frigid final few hours for the month, January was all but certain to beat the previous record set in 1932, the weather bureau said.

The monthly result means the September-January period was also the hottest on record, beating the previous three highest in 2002-03, 2006-07 and 2009-10.

Those earlier years “were all El Nino and drought years, whereas that hasn't been a factor this time,” said Blair Trewin, senior climatologist with the bureau's national climate centre. “That makes it even more remarkable.”

Dr Trewin said that while Australia had a variable climate, the recent heat spell should be seen against the backdrop of longer-term warming.

“If you do super-impose your normal variability on a warming background trend, you are going to see more warm extremes and fewer cold extremes,” he said.

While the bureau rounds off the monthly temperature numbers to 9am on the first day of the following month, its rainfall levels are counted until 9am on the last day of each month.

These show a mixed picture, with some regions along the east coast reporting well-above average rainfall, thanks mostly to the remnants of tropical cyclone Oswald, which dumped record rain on many parts of Queensland and NSW.

By contrast, parts of Victoria posted record low rainfall for the month, particularly in the south west, Dr Trewin said.

Melbourne's tally of 8 millimetres placed it within the 10 per cent of driest years in records dating back to 1855.

The massive heatwave in the first half of the month prompted the bureau to add extra colours to its heat charts in case temperatures climbed above 50 degrees.

While the new colour scheme of purples and pinks for 50-52 and 52-54 degrees has yet to be used, the country did smash previous records dating back to 1910 for days in a row of average maximums above 39 degrees (seven) and the hottest area-average mean temperature at 32.36 degrees.

One of the month's more notable records was Alice Springs, which notched up 17 days in a row over 40 degrees. In 1972-73, the previous time Australia experienced such a broad-based heatwave, the town managed 17 days straight over 39.5 degrees, Dr Trewin said.