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Informist, Wednesday, Sept. 10, 2025

MUMBAI – The Indian Ocean Dipole, which has remained below (-)0.4 degrees Celcius in the last seven weeks, is likely to be classified as a negative Indian Ocean Dipole event in the next few days as it would have remained in the negative threshold for eight consecutive weeks, the Australian Bureau of Meteorology said in its fortnightly report. The negative Indian Ocean Dipole event is likely to continue during spring, with a return to neutral in early summer, the bureau said. 

Spring in the Southern Hemisphere spans from Sept. 22 to Dec. 20, while summer is from Dec. 21 to Mar. 19. The bureau's model prediction is consistent with all international models assessed and the typical Indian Ocean Dipole life cycle, it said. For the week ended Sunday, the Indian Ocean Dipole value was (-)1.27 degrees Celsius. 

The Indian Ocean Dipole is the difference in surface temperatures between the eastern and western tropical Indian Ocean. A negative Indian Ocean Dipole leads to less rainfall in India, while a positive index leads to more rainfall. For monitoring the index, the bureau considers sustained values above 0.4 degrees Celsius for at least eight weeks as typical of a positive index, and values below (−)0.4 degrees Celsius for the same duration as typical of a negative index.

Forecasts from the India Meteorological Department's Monsoon Mission Climate Forecast System, along with other climate models, suggest that weak negative Indian Dipole conditions are likely to persist for a brief period at the end of the southwest monsoon. The withdrawal of the southwest monsoon usually begins around Sept. 17 and ends around Oct. 15.

The El Nino Southern Oscillation is currently neutral, the bureau said. Though atmospheric indicators remain mostly neutral, the sub-surface waters in the tropical Pacific have shown signs of cooling in recent weeks, the bureau said. The tropical Pacific is likely to cool further, potentially reaching La Nina levels briefly during spring, it said. Neutral El Nino-Southern Oscillation conditions are likely to return during summer, it said. 

The bureau's prediction is consistent with most international models it has assessed, with around half of them indicating neutral conditions, and the other half indicating the likelihood of a brief La Nina event. The El Nino-Southern Oscillation stood at (-)0.54 degrees Celsius as of Sunday, with weekly values ranging from (-)0.5 degrees Celsius to (-)0.6 degrees Celsius in the past month, the bureau said. For La Nina to emerge, ocean surface temperatures in the tropical Pacific should meet or fall below the threshold of (-)0.8 degrees Celsius. For El Nino, the temperatures should meet or rise above 0.5 degrees Celsius.

The El Nino-Southern Oscillation refers to the fluctuation between El Nino and La Nina conditions in the Pacific Ocean. El Nino is linked to drier, hotter weather in India, while La Nina results in more favourable rainfall.

According to the Indian weather department, weak La Nina conditions are likely to develop in the last quarter of 2025, though neutral conditions are expected to return post December. Rainfall in September is likely to be above normal at 109% of the long-period average over most parts of the country, the weather department said.  End

Reported by Shreya Shetty

Edited by Avishek Dutta

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