La Niña is over but there is a 50-50 chance another one will graduate in the Australian summer

La Niña is over but there is a 50-50 chance another one will graduate in the Australian summer

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The Australian Bureau of Meteorology has announced the end of the 2021-22 La Niña in the tropical Pacific – but may return with BoM changing its status to “watch”.

La Niña, which involves warming ocean temperatures in the western Pacific, typically provides increased rainfall across much of Australia, along with cooler daytime temperatures south of the tropics and warmer nighttime temperatures in the north.

A senior US government scientist warned less than a fortnight ago that Australia’s east coast could be hit by a rare “triple La Niña” that would bring flooding rains and colder weather for the third consecutive summer in 2022-23.

Sydney had its wettest summer in 30 years in 2021-22 and its wettest March on record. It has already received over 126% of its average annual rainfall this year.

Related: ‘Triple La Niña’: Australia could face another rainy summer, warns US expert

While the previous La Niña is officially over, the BoM’s “observation” categorization means there is a 50% chance that Australia will experience another La Niña event forming this year – twice the normal probability. Winter will likely be wetter than average.

BoM’s head of long-term forecasting Andrew Watkins said a La Niña event three years in a row would be rare, though not unprecedented.

“While back-to-back La Niñas are not uncommon and, in fact, we have them about half the time since 1900, a three-year-old La Niña is less common,” he said. “We’ve only seen it three times since the middle of the last century.”

Watkins said meteorologists had been monitoring La Niña’s weakening for several weeks.

“The ‘observation’ of La Niña does not change the outlook for above-average rainfall for most of Australia in the coming months,” he said.

“The agency’s long-term outlook remains wetter than average, consistent with model outlooks from other global forecasting centers, reflecting a range of climate factors, including a developing Indian Ocean negative dipole (IOD) and warmer waters. warmer than the average in Australia.

“Sea surface temperatures are currently warmer than average over much of the Australian coast, particularly to the north and west. This pattern is likely to increase the chance of above-average winter and spring rains for Australia.”

The IOD – the difference in sea surface temperature between a western pole in the Arabian Sea (west Indian Ocean) and an east pole in the eastern Indian Ocean south of Indonesia – is currently neutral.

But climate modeling suggests that a negative IOD is likely to form in the coming months; winter and spring rainfall in eastern and southern Australia are typically above average during a negative IOD.

Most observations and researched climate models of ocean temperatures and winds over the tropical Pacific Ocean indicate neutral El Niño-Southern Oscillation (ENSO) levels – neither La Niña nor El Niño – are likely to persist through the southern hemisphere winter.

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