Sydney may be in the midst of one of its mildest starts to any spring but clouds are gathering over inland Australia in a big way.
On Monday the city clocked up its 10th day in a row above 20 degrees, and the Bureau of Meteorology is forecasting another seven at least.
If achieved, the 17 days would be the fourth-longest such stint for this time of year, Acacia Pepler, climatologist at the bureau, said. Tuesday may come close to breaking the series with a couple of millimetres of rain and a top of 20 degrees tipped.
Meteorologists and emergency services, though, are increasingly focused on the prospect of heavier falls and possible flooding in the coming weeks across large tracts of inland eastern Australia.
Winter was Australia's second wettest on record – just missing out on a new high by a couple of millimetres, leaving many regions already sodden.
"It's about as wet as it has been in the past 110 years [of records] across Australia," David Jones, head of climate predictions at the Bureau of Meteorology, said. "The set-up is quite extreme."
A plume of tropical moisture uplifted from the Indian Ocean has been combining into a strong line of lows forming in the Great Australian Bight, driving the wet conditions across the Murray Darling Basin, in particular.
And as many as four major rain-bearing systems are predicted over the coming fortnight, bringing more run-off to already water-logged catchments. (See bureau chart below of rainfall totals predicted out to September 19.)
To the northern end of the basin, towns such as Birdsville – normally very dry at this time of year – have already had record September falls, and could double that tally again over the coming week, Dr Jones said.
Western Victoria has seen conditions shift abruptly from record dry a few months ago to widespread floods over the weekend.
Flood watches are in place for minor to moderate inundation over many other catchments from Victoria to Queensland and emergency services are ramping up operations.
"We haven't seen as much water in the system as this since 2012," when three wet years followed in succession, Bernard Kates, Albury-based regional controller for the NSW State Emergency Services, said.
The nearby Hume Reservoir began releasing water into the Murray River last week when dam levels hit 97 per cent. Those releases mean the Murray downstream is likely to see minor flooding or worse for weeks to come.
Unlike the dramatic floods experienced after coastal deluges, water tends to drain only slowly over much of the Murray Darling Basin, Mr Kates said.
"The land is so flat, you end up looking after people for long periods," he said, adding that the SES has been making regular rescues of stranded residents or drivers stuck in flood waters.
Water storages across the basin have jumped from 52 per cent a year ago to 70 per cent now, the bureau said.
Most of the coming week's rainfall will be confined to the west of the ranges, leaving the eastern coastal strip - including Sydney - relatively dry, said Kim Westcott, a meteorologist with Weatherzone.
Along with the rainfall, an early season snow-melt could add to inflows, Dr Jones said.
Most snow below 1600 metres has now gone, which is "unusual for this time of year", he said.
"What we're seeing is a lack of cold," Dr Jones said, adding that "tropical moisture not good for snowfall".
The set-up is mostly related to the Indian Ocean. Temperature differences between the eastern Indian Ocean and the west have been the most extreme in at least 50 years, leading to more uplift of moisture off north-western WA.
The so-called negative Indian Ocean dipole is breaking up but may continue to nudge rainfall to above average levels across eastern Australia until the late spring at least, Dr Jones said.
