Australia is heading for a relatively hot and dry start to summer as key climate drivers combine to raise the fire threat in many parts of the country.
The odds point to about a 70 to 80 per cent chance of below-average rainfall for eastern Australia, extending dry conditions that have set in over much of the region in November, according to the latest climate outlook from the Bureau of Meteorology.
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How to stay safe in a bushfire
As the hot weather returns Russell Jones from DFES offers three tips to stay safe if your property is under threat.
"We are seeing a turn in the weather," said Robyn Duell, a senior climatologist at the bureau, noting that much of the country had an exceptionally wet winter. "If we see a hot December, it will raise the risk [of bushfires] because there's a lot of vegetation around."
The outlook for heightened fire threats matches forecasts made in August that Australia's second-wettest winters on record would lead to a delayed start to the bushfire season before conditions ramped up.
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While southern cities such as Melbourne have had a wildly variable spring, regions further north such as Sydney had recently been recording temperatures well above average and relatively little rain.
So far this month, daytime temperatures in the Harbour City are about 3 degrees warmer than average and rainfall is less than a third of the usual levels for the month.
While odds favour the summer as a whole being warmer than average for eastern Australia, the signal is strongest for December. (See bureau chart below.)
Lower than usual cloud cover will be the feature for much of the summer, and with that rainfall is also likely to be less than typical for both December and summer as a whole,
In December alone, almost the entire continent has odds favouring drier than usual conditions, the bureau said. (See chart below.)
Three-way tussle
Australia has three main influences for rainfall, including the El Nino-La Nina weather pattern in the Pacific. For now, those conditions are basically neutral.
A second influence is the so-called Indian Ocean Dipole (IOD), which had been at record low readings during the winter.
The gauge, which measures relative temperature differences of north-west Western Australia and the east coast of Africa, was the main driver behind the record wet cooler months across much of southern Australia. During a negative-IOD as we have just had, there is more convection off WA and hence, more moisture streaming across the continent.
With La Nina and IOD more or less in the neutral phase, though, the battle to influence Australia's weather is coming down to a dominant so-called Southern Annular Mode (SAM).
During negative-SAM periods, as is currently the case, the belt of strong westerly winds known as the "Roaring Forties" expands towards the equator.
During the spring and summer with such conditions, high-pressure systems sit further north over the country, acting as a barrier to tropical moisture reaching further south, Ms Duell said.
For now, the bureau is still expecting an average to above-average cyclone season for northern Australia, although the current set-up means less of the tropical rain generated by the storms will make it further inland.
A negative-SAM period has been less common, with research indicating that increasing levels of greenhouse gas have tended to contract the westerlies closer to Antarctica since the 1940s.