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Could this finally be the La Niña's last hurrah as rain spreads south?

Pastoralists in North-West Queensland delighted by the unseasonal rain (Supplied: Ben Hann)

As the east coast deals with the latest round of tropical rain after a thoroughly wet season, the big question is if this is all going to end sometime soon.  

There has already been a huge amount of rain in Queensland over the past few days, with more on the way as rain spreads down the eastern seaboard. 

But it is properly into autumn now and the northern wet season is supposed to be over. So is this finally the end of all this tropical rain? 

What's the forecast?

After central Queensland received a drenching yesterday, the focus is expected to shift to the coast today where Jackson Browne, senior meteorologist at the Bureau of Meteorology, has warned that isolated rainfall accumulations of up to 500mm are possible near the great divide. 

As has happened again and again this year, this weather has been set up by what Mr Browne creatively termed the "two-system tango." 

The first partner in this rain dance is the blocking high in the Tasman Sea.

The blocking high feeds moist easterly and even, in this case, north-easterly winds in towards our coast. 

"Lots of tropical moisture coming in from Papua New Guinea and Vanuatu, Solomon Islands, that sort of area," he said. 

The high then partners with an upper-level trough up over Western Queensland.

"So this interaction between the two systems is really a set-up for heavy rain," he said. 

Today a coastal trough and potentially even a low are expected to develop, further enhancing the rain over the coast. 

This round of rain comes just weeks after parts of central Queensland received more than 100mm around Anzac Day. (Supplied: Casey Edgar)

Rain spreading south 

But it is not just Queensland expecting the wet stuff. 

Remote parts of the Northern Territory and South Australia have already received heavy falls and from today the rain is expected to make its way into central northern New South Wales. 

"But the moisture really doesn't have anything to interact as strongly as it is in Queensland," according to Mr Browne. 

Queensland is expected to receive an absolute drenching in the next few days but the rain is certainly not restricted to the sunshine state. (Supplied: Bureau of Meteorology)

"So while there will be rainfall falling in New South Wales, we're not expecting it to be as impactful as that which is falling in Queensland."

From Thursday, the rain is expected to spread into southern New South Wales and northern Victoria. 

Melbourne is not expecting much but Sydney is expected to be wet on Thursday with possible rainfall of 10 to 20mm. 

By Friday, the rain is expected to make it all the way down to Tasmania. 

Is this the La Niña's last hurrah? 

If you are thinking this wet weather has been going on forever now you're not wrong. 

This latest round of rain is "pretty unseasonable", according to Mr Browne. 

"It is May, which is firmly an autumn month. However, we are still getting these very tropical-like features coming through and delivering summer-like rainfall."

Mr Browne said that you could frame this latest round of rain late in autumn as the La Niña's last hurrah. 

But he points out that the last couple of weather systems have been framed that way.

The La Niña has been a stubborn influence in eastern Australia this year. 

Mr Brown said more rounds of tropical rain were still a possibility.

"But indications from the latest guidance suggest that the [La Niña] will decay and the relatively warm patch of warm waters will move out into more central parts of the Pacific," he said.

The BOM's latest climate driver update confirmed that La Niña conditions are persisting over the Pacific. 

But it states that all but one of the climate models it consults indicate that the La Nina is likely to return to neutral conditions by early winter. 

It comes just days after the US National Weather Service's Climate Prediction Center announced there was a 59 per cent chance the La Niña would persist through the Northern Hemisphere summer. 

If the La Niña manages to persist and make it into next summer that would make three La Niñas in a row. 

If a three-peat does occur it would be the third three-peat on the relatively short modern record.

But before we go getting ahead of ourselves, Associate Professor Andréa Taschetto, of UNSW Science's Climate Change Research Centre pointed out that it is not unusual for a La Niña to persist a bit longer than usual.

"We just need to wait a little bit longer for the next forecasts to really confirm that this is coming," she said. 

"This is a really tricky time of the year to be forecasting La Niñas and El Niños.

"Generally, the forecast is a little bit blurry. Autumn time is just a really a tricky time to be predicting." 

Queensland is getting a drenching in the latest round of tropical weather as rain is expected to start moving south today, while a front taps into cyclonic moisture in the west. (Supplied: Bureau of Meteorology)

Autumn's dodgy forecasts are such a well-known factor it even has a name — the "autumn predictability barrier". 

"What I would say is, wait for the next month or so because those predictions will be more accurate," she said.  

The West is getting its own slosh of tropical rain 

Late-season Tropical Cyclone Karim is currently circling well off in the Indian Ocean.

But despite being far out to sea it is still expected to impact the West Coast by helping to pump moisture into a cold front currently lining up the south west. 

Perth is expecting possible rainfall of 20 to 30mm on Thursday. 

"So if we get the upper limit there, we could see around a quarter of the May rainfall for Perth fall on Thursday, which is welcome news," Mr Browne said.

There is an outside risk of heavy rainfall and damaging winds though, according to Mr Browne, so keep an eye on those warnings. 

But in less welcome news for the Top End, after a glimpse of the dry season over the weekend the rain over Queensland has let the moisture back in.

"So a return to more humid conditions for the Top End and the moisture doesn't really clear up until maybe next Monday," according to Mr Browne.

"So it's stickier than usual until then." 

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