La Nina weather event confirmed for Australia this summer

Australians can expect a stormy, cool and wetter than usual summer with a La Nina weather event officially confirmed.

The Bureau of Meteorology on Tuesday afternoon declared a La Nina was under way in the tropical Pacific after weeks of anticipation.

Last summer was also affected by the climate driver, meaning back to back La Ninas for Australia.

The weather bureau issued a La Nina “watch” on September 14, which it ramped up to a La Nina “alert” on October 12.

Much of eastern Australia has been lashed over the past two months by heavy rain and thunderstorms, which last week flooded the Lachlan River catchment in the NSW central west.

The La Nina weather phenomenon, linked to the shifting pattern of sea surface temperatures through the Pacific and Indian Oceans, affects rainfall and temperature variations in Australia.

Typically it is associated with heavier rainfall for eastern, northern and central parts of the country, as well as a higher likelihood of tropical cyclones.

Tropical Cyclone Paddy, the first of the 2021-2022 season, formed near Christmas Island on Monday but the weather bureau says it doesn’t pose an immediate threat to the mainland or any offshore communities.

The category one system will continue to move slowly south before moving west and starting to weaken later on Tuesday.

During La Nina, waters in the central or eastern tropical Pacific become cooler than normal, persistent southeast to north-westerly winds strengthen in the tropical and equatorial Pacific, and clouds shift to the west, closer to Australia.

Andrew Watkins, the weather bureau’s head of operational climate services, said the last significant La Nina event occurred in 2010-2012, bringing widespread flooding and Australia’s wettest-two year periods on record.

“La Nina also occurred during spring and summer of 2020-21. Back-to-back La Nina events are not unusual, with around half of all past events returning for a second year,” he said.

Dr Watkins said that this year’s La Nina was not predicted to be as strong as the 2010-12 event and may even be weaker than the one that occurred last summer.

“Every La Nina has different impacts, as it is not the only climate driver to affect Australia at any one time,” he said.

“That’s why it is important not to look at it in isolation and use the bureau’s climate outlooks tools online to get a sense about likely conditions for the months ahead.”

The weather bureau says this La Nina event is likely to persist until at least the end of January 2022.