La Nina is part of a cycle known as the El Nino-Southern Oscillation, a naturally occurring shift in ocean temperatures and weather patterns along the equator in the Pacific Ocean.

More news: Man in stable condition with serious lower body injuries following Golden Gully crash

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

The Bureau's Head of Operational Climate Services Andrew Watkins said that typically during La Nina events, rainfall becomes focused in the western tropical Pacific, leading to wetter than normal period for eastern, northern and central parts of Australia.

"La Nina also increases the chance of cooler than average daytime temperatures for large parts of Australia and can increase the number of tropical cyclones that form," he said.

"La Nina is also associated with earlier first rains of the northern wet season, as we've observed across much of tropical Australia this year."

Dr Watkins said the last significant La Nina was 2010-12.

He said this was a strong event which saw large impacts across Australia, including Australia's wettest two-year periods on record, and widespread flooding.

More news: Accused burglar denied bail after series of alleged offences

"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 event is not predicted to be as strong as the 2010-12 event and may even be weaker than in 2020-21 La Nina event.

Related: October weather in central Victoria: Wetter than average

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

The Bureau previously shifted to La Nina WATCH on 14 September 2021, and to La Nina ALERT on 12 October 2021. La Nina is likely to persist until at least the end of January 2022.

For more information about climate drivers, visit our website.

Our journalists work hard to provide local, up-to-date news to the community. This is how you can access our trusted content: