Senior meteorologist David Crockett from the Bureau of Meteorology says the low will drive widespread rain and storms over the next three days as it tracks from SA into NSW, Victoria and Queensland.
"We will see a big low-pressure system bringing rain and storms across a vast area of southeast and central Australia over the next three days or so," he said on Monday.
The system developed over WA on Saturday and has already delivered widespread rain and thunderstorms across the west, western SA and the southern NT, including 20-to-30mm in Alice Springs on Sunday.
The low is centred in far-west SA, spreading rain across the state with a risk of severe thunderstorms and damaging winds in the state's north and into southern parts of the NT on Monday.
As the system tracks east, it will move over the Eyre and Yorke peninsulas before passing near Adelaide and the hills, with higher totals possible over already saturated catchments.
"Many of those areas, particularly the Adelaide Hills, are quite wet already following recent rain ... the creeks and rivers are ready to respond quickly to any further rainfall," Mr Crockett said.
The rain band is expected to shift into western NSW and much of Victoria from late Monday and into Tuesday, with the heaviest falls of 40-to-60mm expected early on Tuesday over the northeast Victorian ranges and the southeast ranges of NSW, particularly the alpine regions.
By later Tuesday and Wednesday the focus turns to eastern NSW and southeast Queensland, which can expect generally 5 to 15 millimetres, with higher totals along the NSW ranges.
"This could be the first severe storm of the season for some of those areas, depending on how the storms develop on Tuesday afternoon."Â
Forecasters warn of a broad severe thunderstorm threat on Tuesday afternoon from northern Victoria through western NSW into southwestern Queensland, with heavy rain, damaging winds and possible large hail.
Warnings are in place for the Avoca, Loddon and Murray River around Barham and saturated catchments primed to respond quickly to further rain.
A flood watch covers most northern Victorian catchments where rivers could rise rapidly from Tuesday morning.
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