A hybrid cyclone is set to form off the coast, increasing the chance of more heavy rain and flooding across Victoria, NSW and Tasmania.
Radar images supplied by Weatherzone show two distinct low pressure systems swirling above the east coast.
The first was seen hovering near the junction of the New South Wales, Victoria and South Australian border, with the other over the Tasman Sea, off the north coast of NSW.
Weatherzone explains the systems – a cold-core low and a warm-core low – are on course to crash into one other as they pass over Victoria today.
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When they do, the differing temperatures will lead to the formation of a dynamic and dangerous system called a hybrid cyclone.
"This mix of air leads to a mix of energy sources, which can allow hybrid cyclones to intensify quite rapidly," it said.
"Hybrid cyclones are often caused when one type of low pressure system transitions into the other (e.g. warm to cold core).
"However, this system is different, as it is being caused by two already-established systems combining.
"This will cause the cores to try and balance out each other's core temperatures, resulting in an unstable and dynamically evolving system."
Weatherzone said hybrid cyclones are renowned for causing severe weather, including large tornadoes outbreaks in the United States.
As this system will be offshore, the most likely result will be more heavy rain.
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"(The) most intense weather should occur over water," it said.
"However, this system may still bring heavy rain to parts of the NSW South Coast, Victoria's Gippsland region and the east coast of Tasmania between Monday and Thursday."
While computer models forecast widespread falls between 60-100mm, Weatherzone warned hybrid cyclones can be unpredictable.
"These systems can sometimes produce up to twice as much as forecast," it said.
"It is possible that some areas between southeast NSW and eastern Tasmania could see falls in the range of 100-200mm over the next few days."
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Individually the lows have been responsible for dropping heavy rain over east coast states.
"The western-most low dumped 95.6 mm of rain on Renmark during the 24 hours to 9am on Monday, which was Renmark's highest daily rainfall on record," Weatherzone said.
"During the same 24-hour period, Alstonville in northeast NSW was inundated by 233mm as the Tasman Sea low drove heavy rain into the region.
"Nearby, Ballina's 126.4mm was equivalent to more than a month's worth of rain falling in a single day."
It comes after the news Sydney has had its wettest October in 165 years.
Flood crisis continues
Both NSW and Victoria continue to battle through a deadly floods crisis.
A body was found on the bank of a flooded river in NSW Central West yesterday in the search for a woman missing after escaping a vehicle swept off a flooded causeway north of Mudgee.
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It's the fourth floods-related death in just over the week.
As of 5.30 am, there are 141 flood warnings current across NSW, which stretch from the Victorian border to Queensland.
Of these warnings 23, are at emergency level.
Across the border, residents on the "wrong side of the levee" along the Murray river in Echuca are considering launching legal action.
A resident told 9News, community members plan to meet to discuss the floods response after a makeshift clay levee split the town in two, with some homes deemed "unsaveable".
"We'll talk about class action," they said.
Floodwaters from the Campaspe and Goulburn Rivers have combined with flows down the Murray River to cause major flooding at Echuca and Moama.
"River levels at Echuca Wharf have exceeded the October 1993 (94.77 m AHD) and November 1975 (94.80 m AHD) floods, and may peak slightly below 95.00 metres AHD during Tuesday, with major flooding," the Bureau of Meteorology (BoM) says.
"As this flood peak extends downstream, it is likely to exacerbate the current major flooding at Torrumbarry and Barham, and cause additional river level rises along the Murray River downstream of Barham."
There a 73 warnings current across Victoria.
Of those, five are at emergency level.
