A weakening La Niña could mean a typical Australian summer for the south-east – ABC News

A weakening La Niña could mean a typical Australian summer for the south-east
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It's the news most of south-east Australia has been waiting for: the big wet could be coming to an end.
After nearly three years of rain and flood events the ensemble of wet climate drivers, led by a triple La Niña, is rapidly breaking down.
In other words, ocean and wind patterns surrounding Australia either have or are showing signs of returning to normal.
While La Niña gets most of the attention, the Indian Ocean is no second fiddle when it comes to controlling Australia's weather.
A strong positive phase helped cause the Black Summer bushfires, while a strong negative phase was instrumental in this year's record wet spring and flooding across NSW and Victoria.
The negative phase, called a -IOD, characterised by warm waters and rain on Australia's side of the basin came to an abrupt conclusion through November. 
The rapid stabilisation of the Indian Ocean was expected as the summer monsoon takes control of the weather across the tropics.
However, what is a pleasant surprise is the Southern Ocean has also moved to neutral territory in recent weeks.
Simply put, the belt of westerly winds encircling Antarctica, called the polar vortex, has weakened and a weaker vortex allows dry westerly winds to expand north towards southern Australia.
There is no guarantee this shift will be permanent through summer, but the Bureau's latest forecast for the Southern Ocean is either for a neutral or weakly positive phase during the coming weeks and months.
This will mean a brighter outlook than the strong positive phase which has dominated the past three years and allowed humid easterly winds to flood the eastern seaboard. 
That just leaves La Niña as the sole climate driver still capable of producing a wet miserable summer, but even the often-immovable force of La Niña is showing signs of waning.
During the past few weeks, the equatorial Pacific has warmed below the surface.
The catalyst for warming at the surface would trigger the decoupling between the ocean and atmosphere that leads to flooding in eastern Australia.
Global models are now also leaning towards an early end to La Niña and possibly even a rapid transition to El Niño next year.
If La Niña does indeed weaken and the Southern Ocean remains near neutral, then a typical Australian summer is on the cards.
Although, there is often a multi-week lag between changes in the ocean and the atmospheric response.
In other words, the La Niña impact can last a few weeks beyond when the Pacific is neutralised.
So what would a typical Australian summer look like? For most regions compared to the past two summers, expect more sunshine and warmer temperatures.
A regular run-of-the-mill summer will still include thunderstorm outbreaks, tropical cyclones and bouts of flooding, but the risk of widespread major flooding is greatly reduced without the aid of global and regional climate drivers.
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