Heavy rain, thunderstorms, damaging winds and cold temperatures will sweep across much of central and southeastern Australia in the coming days.
A giant low pressure system of tropical moisture stretching from Darwin to southern Australia is expected to intensify on Wednesday night above Victoria, with flash flooding possible in the state's west and centre.
Rain bursts of up to 60mm are predicted in the north and dividing ranges with overall falls up to 120mm, the Bureau of Meteorology says.
Senior forecaster Kevin Parkyn said the system heralds the onset of the La Nina weather pattern, which will deliver a wetter summer.
"The atmospheric conditions are just ripe for that system to intensify tonight right over Victoria," he said.
"We call that process cyclone genesis. This system is linked to tropical moisture, we haven't seen that for quite some time."
A severe weather warning is in place for much of the state's north and centre, with the system to head south on Thursday.
Victoria will experience widespread rain of 10-30mm, while Melbourne will get up to 20mm - an amount that would push the city past its average annual rainfall.
Damaging winds with gusts reaching 100km/h are likely in Victoria's eastern alpine areas from Thursday.
Heavy rain is also forecast in eastern South Australia on Wednesday night, with the system to hit Tasmania on Thursday.
Up to 90mm is expected in the island state's north and higher falls are possible in elevated areas.
In a video posted to BOM’s Twitter page, Meteorologist Dean Narramore said temperatures will drop as low as 16C below average for October.
He also said he expects wind to damage and knock down trees in Victoria and Tasmania.
Emergency crews are on alert in the north with soil already damp from recent rain and high winds predicted.
Severe Weather Update: significant rainfall to bring flooding to parts of southeastern Aust. Video current as at 1.00pm AEST, Tues 6 Oct 2020.— Bureau of Meteorology, Australia (@BOM_au) October 6, 2020
For the latest forecasts & warnings check our website at https://t.co/v2sYSWnni5 & follow advice from emergency services @ABCemergency pic.twitter.com/x8WeKOSKjO
"These winds will likely cause trees and tree limbs to fall," SES regional manager Mhairi Revie said.
Ms Revie implored motorists to drive safely at a time when roads are extra busy due to school holidays.
Potentially damaging winds are also tipped in elevated areas of southern NSW on Thursday morning.
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