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BOM indicates drenching La Niña is set to hang around until late autumn

We have now officially been under La Niña conditions since November. (Supplied: Bureau of Meteorology)

The BOM's latest climate driver update has indicated the rain-bearing La Niña is set to hang around for a while longer yet. 

The La Niña passed its peak in January and had been slowly declining but it is now looking like the climate driver could linger until late autumn.

Not good news for those sitting in already sodden catchments.

As Andrew Watkins, head of long-range forecasts at the Bureau of Meteorology explained, the normal cycle for a La Niña is for it to break down during autumn.

Things seemed to be on track this year until the trade winds strengthened a few weeks ago.

"That strengthening of the trade winds has gone and caused a cooling of the surface in the tropical Pacific and so we've seen some of the numbers go back down into La Niña territory," he said.

The news comes as the tropical climate driver, the Madden Julian Oscillation (MJO), swings around to provide another tropical kick in the coming weeks.

Dr Watkins said that most models were predicting that while it might weaken a little bit, a burst of the MJO is expected to move over the region north of Australia over the next fortnight or so.

"That could potentially bring periods of wetter conditions and increase the risk of tropical cyclone and tropical low formation," he said.

"Overall, the outlook is continuing to look at above average rain for the next month."

The highest likelihood of above-average rainfall is in the north but Dr Watkins warned that places down the east coast could see more heavy rainfall on their already sodden catchments over the next couple of weeks.

"So unfortunately, not heading into the dry period that we would all like to see at the moment," he said.

"We can't quite relax just yet."

Why have the trade winds strengthened?

OK weather nerds, tuck in.

According to Dr Watkins it's not completely clear why the trade winds have strengthened.

"It may be associated with the Madden- Julian Oscillation hanging out in the western Indian Ocean," he suggested.

A La Niña generally brings wet and warm conditions to Australia. (Supplied: Bureau of Meteorology)

Climate scientist Agus Santoso of the University of New South Wales also pointed to new research that indicated that the Atlantic Ocean could also be playing a part.

"It seems like when the Atlantic is warmer than normal it is conducive for La Niña conditions," he said.

Sure enough, he notes there is currently a warmer-than-normal Atlantic Ocean.

"That is quite unusual because when we have a La Niña it will tend to lead to a cooler North Atlantic," he said.

Why we are having a warm Atlantic mid-La Niña is then the next in the domino line of questions that always tend to line up when looking into these interconnected global climate systems.

According to Dr Santoso, it could be because of global warming.

"Because we're warming, it tends to warm everywhere around the world's ocean," he said.

These are just a few of the factors that could be at play here and, of course, it never pays to rule out the impact of general variability.

It is also worth noting that La Niñas are generally more likely to linger late into autumn than El Ninos.

When will the La Niña end?

There is no promise that the La Niña will definitely, definitively end anytime soon.

We are now on the second La Niña year in a row and, as Dr Santoso points out, having three in a row is certainly possible.

"It has happened before," he said.

"In 1998, 1999, 2000 there were three consecutive La Niñas and in 1973, 1974, 1975."

But a three-peat would be pretty uncommon, and according to Dr Watkins all but one of the models the BOM uses to predict the La Niña are indicating a return to neutral conditions by June.

But, before you throw your rain dancing shoes onto a pile of flood debris, remember the other side of the coin has its own dangers.

"If we have an El Nino at the end of the year, which is also not impossible, it would be catastrophic," Dr Santoso said.

"Because when we have La Niña we have lots of leaves growing and that can be a fuel for forest fires," he said.

As we saw with the rapid onset of the drought in 2017, it doesn't take long for things to swing to the opposite extreme.

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