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Unprecedented weather phenomenon showing signs of ‘slowing down’

After the Bureau of Meteorology (BoM) released its latest climate update this week, a leading Australian weather expert said there is now a lower chance of a La Niña event occurring in late 2024, meaning there is less chance of rainfall in the second half of the year than initially feared.

In recent years, the terms El Niño and La Niña have been frequently used in Australia. El Niño brings drier and warmer than average conditions, while La Niña brings above average rainfall and cooler daytime temperatures for most.

In May, the bureau said there was a 50 percent chance that a La Niña pattern would sweep across the eastern half of the year. While that is still possible, it is less likely.

Australia has experienced three La Niña events, each followed by an El Niño, between 2020 and 2023. Another La Niña event would mean the extreme weather event has been declared for five years in a row – something experts have previously said is unprecedented and unusual.

Speaking to Yahoo News Australia, Dr Tom Mortlock from the UNSW Climate Change Research Centre explained what had changed between the Bureau’s May report and its July update. He said that while we are currently in a neutral phase of ENSO – meaning there will be neither an El Niño nor a La Niña – that doesn’t mean things won’t change in the spring.

The Bureau of Meteorology still has a La Niña warning, but the chances of one occurring this year have changed. Source: BoM/Getty

“The only change I see is that in May, of the seven global climate models that the BoM studies suggested that we would have a La Niña system early in the spring,” Mortlock told Yahoo. “Now, if you look at the same set of models, only two of them are.

“If anything, it’s slowing down a bit. The BoM is still saying we’re in a ‘watchful’ phase, but now we have two of those seven models — so five of them suggest ENSO neutral. Even though they’re saying ‘watchful’ is a 50 percent chance of La Niña developing by spring, I think the consensus is that things are slowing down compared to May.”

RELATED: What El Niño and La Niña mean for Australians

While many had expected the heavy rainfall that has hit New South Wales in recent weeks, particularly around Sydney, to be a sign of an approaching La Niña event, Mortlock said weather conditions in the run-up to spring were “not very important” in determining whether a La Niña event would occur.

While many had predicted that the heavy rainfall in New South Wales in recent weeks could indicate an approaching La Niña, weather conditions in the run-up to spring are “not really significant.” Source: Getty

“These global models look at the temperature anomalies in the Central Pacific,” he explained. “They are based on the part of the Pacific Ocean and the sea surface temperatures in that area and whether those sea surface temperatures are warmer or cooler than the long-term average.

“If the temperature is -0.8 degrees below the long-term average, then it is officially called La Niña, and if it is 0.8 degrees above the long-term average, then it is officially called El Niño.

“That’s just the international definition… but that doesn’t necessarily mean we’re going to have more floods, more cyclones, more rain in eastern Australia because of that.”

The office, Mortlock said, is often one of the last agencies in the world to call out El Niño or La Niña across Australia because they have a “slightly different, more complex” and more accurate definition.

“They use something called the Southern Oscillation Index, which is the pressure difference between the observation station in Darwin and the station in Tahiti,” he said. “Basically what it does is it looks at the atmosphere and also the ocean, and really, when those two things line up, that’s when we know we’re really in science territory.”

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