A “La Nina watch” has been issued with some early signs pointing to the weather event that brings rains and floods to Asia, particularly India, forming in the Pacific Ocean later this year by the Australian Bureau of Meteorology (BoM).

At the same time, neutral conditions of the El Nino -Southern Oscillation (ENSO), a climate pattern that occurs when the temperature of central and eastern Pacific Ocean changes, will continue at least until July 2024.

However, the development of positive Indian Ocean Dipole (IOD) or Indian Nino, which could help India get more rains during the south-west monsoon, has stalled, the Australian weather agency said.

The “La Nina” watch comes a month after BoM declared that El Nino, which emerged in June 2023 and led to deficient rain and drought across parts of India, was over.  

Seas cooling since Dec

Currently, the El Nino-Southern Oscillation, a climate pattern that occurs when the temperature of the central and eastern Pacific Ocean changes, is neutral. Given the early signs, the Bureau’s ENSO Outlook has shifted to El Nino watch, it said.

“When La Niña Watch criteria have been met in the past, a La Niña event has subsequently developed around 50 per cent of the time. There is about an equal chance of neutral ENSO conditions in the same outlook period,” said BoM.

Sea surface temperatures (SSTs) in the central Pacific have been steadily cooling since December 2023. This surface cooling is supported by a significant amount of sub-surface cooling in the central and eastern Pacific, it said. Recent cloud and surface pressure patterns are ENSO-neutral.

US agency prediction

Meanwhile, the Climate Prediction Center (CPC), an arm of the US National Oceanic and Atmospheric Administration, said a transition from El Niño to ENSO-neutral will likely take place next month.

“La Niña may develop in June-August 2024 (49 per cent chance) or July-September (69 per cent chance),” it said in its current status and predictions on ENSO.  

The emergence of El Nino in June 2023 has also resulted in global temperatures being warmest for the respective 11 months since then. Global sea surface temperatures (SSTs) have been the warmest on record for each month between April 2023 and April 2024, with April 2024 SSTs warmer than April 2023. 

Carlo Buontempo, Director of the Copernicus Climate Change Service - managed by the European Commission- said: “El Niño peaked at the beginning of the year and the sea surface temperatures in the eastern tropical Pacific are now going back towards neutral conditions.” 

If positive IOD develops

On the other hand, IOD has currently turned neutral. The most recent value of the IOD index (+0.22 °C) is the second consecutive weekly value within historically neutral thresholds. The index has returned to neutral after being above the positive threshold  (+0.40 °C) for 7 weeks in a row.

A positive IOD is considered to emerge if the IOD index sustains above +0.40 °C for at least eight weeks.

“The current SSTs observations suggest that recent development of a positive IOD may have stalled. If a positive IOD eventually develops, it would be earlier in the calendar year than is typical historically,” the Australian weather agency said. 

 “Atmospheric indicators in March and April also indicated that a positive IOD event may have been developing. However, the latest SST and atmospheric observations suggest any potential development may have stalled,” the BoM said.

Monsoon booster

However, the latest forecasts suggest a weaker positive IOD than earlier forecasts. 

A week ago, BoM positive IOD will likely re-emerge for the second consecutive year in the latter half of 2024. The agency also said all five international models surveyed by it suggested positive IOD conditions in May. 

A positive IOD can boost the performance of India’s southwest monsoon, depending on when it develops. For example, in 2019, a strong IOD event that developed during the late monsoon season compensated for a 30 per cent rainfall deficit in June.

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