Positive IOD may emerge again alongside record-breaking El Nino: Australian met body

The event is expected to continue into autumn (March) 2027, given its current strength and the typical life cycle of an El Nino. | Photo Credit: MUSTAFAH KK

A powerful El Nino is tightening its grip on the Pacific, with more warming expected through spring. The Indian Ocean Dipole (IOD) remains neutral, but there is still the possibility of a positive phase, according to the Bureau of Meteorology (BoM) Southern Hemisphere monitoring report.

The latest IOD index value for the week ending August 30 is +0.22°C. The index has been neutral for the past 3 weeks, after exceeding the positive IOD threshold (+0.4°C) for the previous 3 weeks.

The Indian Ocean Dipole is a climate pattern that impacts the Indian Ocean. During a positive phase, warm waters are pushed to the western Indian Ocean, while cold deep waters rise to the surface in the eastern Indian Ocean. The pattern is reversed during the IOD’s negative phase.

Models continue to suggest a positive IOD could develop during the Southern Hemisphere spring (September-November), although the forecast magnitude of the event has decreased in recent model runs.

The most recent relative Nino 3.4 index value for the week ending August 30 is +2.45°C, well above the El Nino threshold (+0.80°C).

Models project warming of the tropical Pacific during the Southern Hemisphere spring, with a likely peak in late spring or summer. Relative-Nino3.4 values are predicted to be warmer than the warmest values observed since reliable records began in 1950.

The report said that this event is expected to continue into autumn (March) 2027 due to its current strength and the typical life cycle of an El Nino.

In the atmosphere, a strong El Nino is also indicated by weakened or reversed trade winds in the western to central tropical Pacific, enhanced cloudiness in the central to eastern tropical Pacific and reduced cloud cover over the Maritime Continent.

The sea surface temperature (SST) analysis for the week ending August 30 shows warmer-than-average waters around much of Australia and mostly near-average temperatures to the north. Waters are particularly warm along the southern New South Wales and eastern and southern Tasmania coasts, where they are around 2–3°C above average.

More broadly, global daily SSTs (60°S to 60°N) have been record-warm in August, exceeding the previous daily record set in 2024.

The Southern Annular Mode (SAM) index has been mostly negative over the last fortnight and remains negative as of August 30. It is expected to stay in a negative phase until at least mid-September.