Australia's Bureau of Meteorology has declared a La Niña has developed in the Pacific, guaranteeing a soggy summer for eastern and northern Australia.
During La Niña, waters in the central or eastern tropical Pacific become cooler than normal, with winds strengthened and clouds shift to the west, closer to Australia.
The Bureau has declared that a #LaNiña has developed in the tropical Pacific. Typically during La Niña, there is above average rainfall for eastern, northern and central parts of Australia. pic.twitter.com/4KJeKsVI6A— Bureau of Meteorology, Australia (@BOM_au) November 23, 2021
The Bureau’s Head of Operational Climate Services Dr Andrew Watkins says typically during these events, rainfall becomes focused in the western tropical Pacific, leading to a wetter than normal period for eastern, northern and central parts of Australia.
The last significant La Niña was 2010–12, bringing large impacts across the country, including Australia’s wettest two-year periods on record, and widespread flooding.
"La Niña 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," Dr Watkins says.
"La Niña is also associated with earlier first rains of the northern wet season, as we've observed across much of tropical Australia this year."
The weather event also occurred during spring and summer of 2020-21.
Dr Watkins explains this year's event is not predicted to be as strong as 2010-12, and may even be weaker than in 2020-21.
"Every La Niña has different impacts, as it is not the only climate driver to affect Australia at any one time," he says.
"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 Bureau says La Niña is likely to persist until at least the end of January 2022.