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Extreme weather on the way as tropical cyclone, southern low pressure system develop in the east

Kate Doyle, Thursday December 13, 2018 - 10:58 EDT
ABC image
Rainfall forecast from the 12th to the 19th of December 2018. - ABC

Two weather systems are coming together to create a deluge that is set to pummel much of the eastern seaboard in the coming days, with the Bureau of Meteorology issuing severe weather warnings in several states.

A low-pressure system expected to form in northern Victoria or southern New South Wales today could bring a month's worth of rain in a day in the south-east.

Meanwhile Tropical Cyclone Owen is intensifying in the Gulf of Carpentaria and is expected to strengthen to hit Queensland on Friday.

It is and could be a category four when it makes landfall.

"What is really interesting is how the two systems are linked by the upper trough," the BOM's extreme weather desk manager James Taylor said.

"It will be the upper trough that develops the low over south-eastern Victoria that drags Tropical Cyclone Owen more towards the east and probably south-eastwards over the weekend.

"That creates a potential threat for large parts of the eastern Queensland coast, particularly from flash flooding."

He said the trough would draw in moisture from the Tropics and Cyclone Owen today and tomorrow and create a heavy rainfall risk from a cloud band with embedded thunderstorms over a large part of the eastern seaboard.

Mr Taylor said the heavy rainfall risk would be for large parts of Victoria and northern and eastern Tasmania.

There is also a chance of extreme conditions in South Australia's south-east as well as eastern NSW, and up along the coast of Queensland.

"We've got a real risk with heavy rainfall, but there's also damaging to destructive winds associated with [Tropical Cyclone] Owen that we need to worry about," he said.

Could it be another Debbie?

Some of the models suggest that Cyclone Owen could track south through Queensland, which will put a shiver through the spine of those who remember Cyclone Debbie, which moved down the Queensland coast in 2017 as an ex-tropical cyclone and brought widespread flooding all the way down across the NSW border.

Debbie caused schools across south-east Queensland to close and has been linked to multiple deaths.

Mr Taylor said this cyclone is very different, more like Cyclone Oswald from 2013. He said it has the potential to move down inland of the Queensland coast, like Oswald, but that the storms movements were still uncertain.

"We won't be able to be certain about it until probably Friday afternoon where we know where TC Owen is in relation to that upper trough."

Wet day for Victoria Thursday

Back down south, Mr Taylor said winds are probably less of a concern than up where the cyclone is making landfall. But there could be damaging wind gusts associated with thunderstorm activity.

He said that while large hail is also a threat with storms, the wind threat or the hail threat would be a lot more isolated and broadly less of an impact than what we might see in terms of rainfall.

That rainfall had made it a .

"We will see the development of that cloud band and potentially even some thunderstorm activity around Melbourne [during the morning] as that low pressure system starts to develop and deepen," he said.

The rain is expected to increase through the day but to clear for Melbourne on Friday afternoon.

How does this compare with the Sydney storm?

Mr Taylor said this systems were quite different in its formation to the but that the impacts could be comparable. Sydney had up to 70 millimetres fall in an hour associated with that low.

He said rainfall rates like those experienced in Sydney were not out of the question over the next few days.

"But it's unlikely that it would be with every thunderstorm, but any thunderstorm has the potential for flash flooding and some impacts, so please stay on top of the thunderstorm and warning service," he said.

"We've got a warning current for central parts of the state and north-eastern Victoria and that is for heavy rainfall, but we will have flood watches for riverine flooding mostly through similar area.

"The Greater Melbourne area is included in that."

Will it break the drought?

When asked if this combination of events could break the drought in Queensland, NSW and eastern Victoria, Mr Taylor said,

"I would love to be able to say 'yes', but I just can't."

According to Mr Taylor parts of western NSW and south-western Queensland, are unlikely they are going to see much rain from this event.

He said this is because the cloud band that links the two systems today is more likely to be over eastern NSW and up through eastern parts of Queensland.

"The thunderstorm activity means that we could see some really decent rainfall totals in some of those areas, but it might be the sort of set-up where your farm gets 30-50 millimetres, maybe even more, but your neighbour misses out. It will be quite hit-and-miss," said Mr Taylor.

"Many places have a decent chance of seeing their wettest day this year."

But in terms of breaking daily rainfall records, he said that looked unlikely — but it would depend on the placement of thunderstorms and that cloud band.


© ABC 2018

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