Melbourne posted its fifth-driest September on record, with no days recording more than 5 millimetres of rain – only the second time that’s happened for that month in records going back to 1855.
Sydney’s rainfall was less extreme, coming in about one-quarter below average.
A lack of rain has been a standout feature of much of eastern Australia this year, drying out soils and forests. All of NSW has been declared in drought, while the fire season has started early and is forecast to be an active one.
The Murray-Darling Basin, Australia’s food bowl, had its driest January-September since 1902 – the end of the Federation Drought – Dr Trewin said.
For the rest of the year, the bureau’s outlook suggests odds particularly favour drier than average conditions in Victoria, southern South Australia and Tasmania.
“The signal in the outlook [for October to December] that’s really strong is warmth,” Dr Trewin said, noting that almost all of the country has an 80 per cent chance of warmer than usual maximum and minimum temperatures.
For September, daytime temperatures were 1.41 degrees above the average for the 1961-90 period.
In both Sydney and Melbourne, maximum temperatures were slightly above the September average. Night-time temperatures, though, were cooler than average in the Victorian capital and only a tad above the norm in the Harbour City.
A notable patch of cold weather last month was in inland south-eastern Australia, where a range of places such Rutherglen and Wangaratta in Victoria posted their coldest Septembers for mean daily minimums. Some regions suffered severe frost, such as the Wimmera.
Nationally, 2018 is likely to be at least a top-10 year for warmest temperatures, Dr Trewin said. Year-to-date temperatures were so far the sixth warmest in records going back to 1910.
The main influence for the dry spell is currently the conditions in the Indian Ocean that favour less convection near the WA coastline, and therefore less moisture streaming across the continent. An El Nino, if one forms in the Pacific later in the year, could exacerbate the drought by shifting rainfall away from eastern Australia.
Peter Hannam is Environment Editor at The Sydney Morning Herald. He covers broad environmental issues ranging from climate change to renewable energy for Fairfax Media.