A positive Indian Ocean Dipole (IOD), which helps in good rainfall over the Indian sub-continent and the African coastline, will likely develop during September-December with all models indicating such a development, the Australian Bureau of Meteorology  (BoM) said on Tuesday. 

IOD is the difference in sea surface temperatures (SSTs) between two areas or poles. hence a dipole. The prediction should bring relief to India since any rains, particularly under the influence of north-east monsoon, from now onwards, will help rabi season crops such as wheat, pulses and oilseeds.

“The IOD index is +1.13 °C for the week ending September 10. This is its fourth week above the positive IOD threshold (+0.40 °C), with the recent high values (above +1.0 °C) indicating an event is very likely. If the IOD index continues to remain above this threshold, a positive IOD event will be considered underway,” BoM said in its latest El Nino update.

Influence on El Nino

While the Indian subcontinent and African coastline will stand to benefit with better rains, it will affect rainfall over Indonesia, South-East Asia and Australia. “A positive IOD typically decreases spring rainfall for central and south-east Australia and can increase the drying influence of El Nino,” the Bureau said.

The Australian weather agency said the long-range forecast indicated warmer and drier than average conditions across most of southern and eastern Australia from October to December. 

“The Bureau’s El Nino Alert continues, with El Nino development likely during spring (September-December). When El Nino Alert criteria have been met in the past, an El Nino event has developed around 70 per cent of the time,” the BoM said.

Sea surface temperatures (SSTs) in the tropical Pacific are exceeding El Nino thresholds and have warmed up over the last fortnight.  Further warming is likely and SSTs may remain above El Nino thresholds until at least early 2024.

“The 90-day Southern Oscillation Index (SOI) is currently -7.4, exceeding El Nino thresholds. Other atmospheric indicators have recently shown signs of possible coupling between the Pacific Ocean and the atmosphere,” it said. 

Indications near Indonesia

This coupling is characteristic of the El Nino event. This will strengthen and sustain the event for an extended period.  

Meanwhile, the Climate Prediction Center (CPC), a unit of the US weather agency National Oceanic  and Atmospheric Administration, in its latest update issued on Monday night, said indication of suppressed convection and precipitation, known as outgoing longwave radiation (OLR) were evident in South-East Asia, the Philippines and Indonesia.

In particular, evidence of El Nino emerging was evident near Indonesia, the CPC said, reiterating that all models were indicating El Nino persisting through the northern hemisphere winter during 2023-24.

The US weather arm said over the last four weeks equatorial SSTs were above average across most of the Pacific Ocean, the Indian Ocean and across much of the Atlantic Ocean.

There were other indicators of El Nino having set in such as upper ocean heat anomalies and declining difference in the temperature on the sea surface and its bottom. 

El Nino, caused by a rise in the Pacific Ocean temperature, leads to drought and deficient rainfall in Asia. The weather phenomenon resulted in India witnessing its driest August in over 120 years with monsoon rainfall being 32 per cent deficient. However, the emergence of positive IOD is in line with predictions that rainfall will improve from September onwards in India. 

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