Though three of the four criteria for the El Nino weather phenomenon to develop have been met, the Pacific Ocean and atmosphere have yet to become fully coupled, as occurs during El Niño events, the Australian Bureau of Meteorology (BoM) has said.
But central and eastern Pacific sea surface temperatures (SSTs) are exceeding the El Nino threshold. “Models indicate further warming is likely, with SSTs remaining above El Niño thresholds until at least the end of the year,” the Bureau said in a new update on Tuesday.
El Nino impact
The El Nino Southern Oscillation (ENSO) outlook remains at El Nino alert. “When El Niño alert criteria have been met in the past, an El Niño event has developed about 70 per cent of the time,” it said.
El Nino is caused by the warming of SSTs in the Pacific Ocean and it leads to drought and deficient rainfall in Asia, particularly India.
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“The past month has seen the Southern Oscillation Index (SOI) shift back to neutral levels, with the 30-day SOI at +3.9 for the 30 days ending July 16. The 90-day SOI is outside El Niño thresholds at -5.2,” BoM said.
Sustained changes in wind, cloud, and broad-scale pressure patterns towards El Niño-like patterns have not yet been observed, the Bureau said justifying why the Pacific Ocean and atmosphere are yet to become fully coupled.
‘Watch’ to ‘alert’
On July 6, the Australian weather agency upgraded its El Nino watch, which means a 50 per cent chance of the weather event setting in, to El Nino alert, a 70 per cent chance for it to occur.
Meanwhile, the Indian Ocean Dipole (IOD) is currently neutral. “All models suggest a positive IOD is likely to develop in late winter or early spring,” BoM said.
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A positive IOD typically decreases rainfall and aggravates the El Nino situation.
Earlier this month, Bureau of Meteorology Senior Climatologist Catherine Ganter said climate models and indicators “now meet the Bureau’s El Niño alert criteria”.
Need to strengthen
“While the models show it’s very likely the tropical Pacific Ocean temperatures will reach El Niño levels during winter, we have seen some movement in the atmosphere towards El Niño conditions,” Ganter said.
Though the alert criteria have been met, the changes will need to strengthen and sustain over a long period to be considered an El Nino event, she said.
Ganter said even if an El Niño develops, its impact can vary depending on the region as well as from event to event.
El Nino typically occurs once in five years. This year’s El Nino event has been predicted after a gap of seven years after three continuous years of La Nina, which leads to excess rainfall in Asia and results in dry phase in South America, during 2021-23.
The US Climate Prediction Center has predicted that El Nino could last at least until April 2024.