The WMO has flagged a second major climate pattern developing alongside El Niño. It co-occurred in 1997–98. Here's what it does — and what it doesn't.
Everyone watching the 2026 El Niño is staring at the Pacific. Weekly Niño 3.4 readings. Subsurface Kelvin wave activity. RONI progression. Model plumes out of ECMWF and CFSv2. All Pacific, all the time.
There is another ocean worth watching.
In its June 2026 update, the World Meteorological Organization explicitly flagged the Indian Ocean Dipole — a climate pattern in the Indian Ocean — as a co-developing factor that "may develop into a positive phase, peaking concurrently with the intensifying El Niño." Climate Impact Company put out a full forecast in March calling for a moderate-to-strong positive IOD to emerge alongside El Niño mid-to-late 2026.
This combination has a historical precedent. The 1997–98 El Niño — the benchmark every current discussion gets measured against — had a co-occurring extreme positive IOD event. That pairing contributed to severe drought across Australia and Indonesia and catastrophic flooding in East Africa.
2026 may be setting up with a similar two-ocean risk — though as of mid-June, the IOD has not yet been declared. The Bureau of Meteorology's June 14 reading puts the Dipole Mode Index at −0.13°C, still neutral. Models are signaling a positive phase is likely in winter-spring, but timing and strength vary across the ensemble.
The Indian Ocean Dipole (IOD) measures the difference in sea surface temperature between the western and eastern equatorial Indian Ocean. Think of it as an El Niño-like seesaw, but operating entirely within the Indian Ocean basin rather than the Pacific.
In its positive phase (+IOD): the western Indian Ocean — near the Horn of Africa — runs warmer than average, while the eastern Indian Ocean near Indonesia and Australia runs cooler than average. The warm anomaly in the west drives enhanced convection and rainfall over East Africa. The cool anomaly in the east suppresses rainfall over Indonesia and northern Australia.
In its negative phase: the opposite. Warm water pools near Indonesia, cool water sits in the west, rainfall shifts accordingly.
The IOD is not a permanent feature — it tends to develop between June and October, typically peaking around September and November, then collapsing rapidly after the Australian monsoon onset in December. That seasonal window maps almost exactly onto El Niño's developing phase.
The physics are linked. During El Niño, trade winds across the equatorial Pacific weaken. That weakening propagates westward, reducing the wind-driven upwelling near Indonesia. When Indonesia's coastal waters warm less than usual — or actively cool relative to the western Indian Ocean — the temperature gradient that defines a positive IOD begins to take shape.
The relationship is not deterministic. Not every El Niño produces a +IOD, and a +IOD can develop without El Niño. But the correlation is robust enough that forecasters treat them as likely companions during strong El Niño events. Climate Impact Company's analog set for 2026 includes 1997, 1999, 2017, 2023, and others — the strong El Niño analogs within that set (1997, 1999, 2023) all produced significant +IOD events, supporting elevated +IOD risk for 2026.
The IOD's direct teleconnections are most pronounced in the Indian Ocean basin. For U.S. readers, the honest answer is that the IOD affects you mainly through indirect pathways — primarily by amplifying global temperature anomalies and modulating the broader Walker Circulation. But for a significant portion of the world's population, it's the more immediately relevant signal.
| Region | El Niño Signal | +IOD Effect | Combined 2026 Outlook |
|---|---|---|---|
| Australia (east/northwest) | Drier | Reinforces drying | Significantly drier |
| East Africa (Horn) | Wetter | Amplifies rainfall | Elevated flood risk |
| India (monsoon regions) | Tends drier | Partially offsets | Below avg, uncertain |
| Indonesia / Maritime Continent | Drier | Reinforces drying | Drought conditions likely |
| Southern U.S. | Wetter (jet stream) | Indirect only | El Niño pattern dominates |
Australia is where the two patterns stack cleanly. El Niño alone tends to suppress rainfall across eastern and northwestern Australia. A positive IOD reinforces that suppression by cooling the waters near Indonesia that feed Australia's monsoon system. In 1997–98, the combination drove one of the most severe droughts Australia had seen in decades. Climate Impact Company's 2026 forecast — using the 1997 and 2023 analogs — points toward the same signal for the east and northwest coasts.
While El Niño tends to bring drought to parts of the tropics, equatorial and southern East Africa is one region where El Niño often increases rainfall rather than reducing it. A +IOD amplifies this further — the warm western Indian Ocean drives enhanced convection inland toward Kenya, Uganda, Somalia, Tanzania, and Rwanda. ICPAC's current outlook flags elevated flood, flash flood, and landslide risk for equatorial and southern Greater Horn of Africa during the October–December season. The northern GHA is a different story — ICPAC expects drier-than-normal conditions there through July–September, before the wet OND signal takes over in the south.
India's 2026 southwest monsoon forecast involves all three factors: El Niño, a developing +IOD, and Eurasian snow cover anomalies. India's Meteorological Department has forecast monsoon rainfall at 92% of the long-period average — classified by IMD as below normal (their published category is 90–95% LPA). The complication: while El Niño tends to weaken India's monsoon, a +IOD tends to support it. IMD scientists noted that positive IOD development and below-normal snow cover "could counter some impacts of the El Niño conditions." The net result is genuine uncertainty — below-normal nationally, with significant regional variance.
The IOD does not change the Pacific picture. The IRI's June 17 weekly Niño 3.4 reading is +1.7°C (NOAA CPC's June 11 Diagnostic Discussion showed +0.7°C at that time — the weekly values have continued climbing since). The RONI trajectory is firmly El Niño. The IRI's June outlook has El Niño probabilities at 100% through SON, 99% into DJF. None of that shifts with IOD status.
What +IOD adds is amplification in specific regions — and a reminder that 2026's climate story is being written by more than one ocean. The 1997–98 analog keeps coming up in model comparisons. When people cite that event, they're usually citing the Pacific signal alone. But 1997–98 also had a record +IOD. If 2026 follows the same script, the Australian drought signal gets cleaner, the East Africa flood risk gets more acute, and India's already-uncertain monsoon outlook stays genuinely uncertain.
For U.S. readers: the IOD's influence on your winter is indirect — filtered through the Walker Circulation and global temperature baselines rather than direct teleconnection. The El Niño jet stream pattern remains the dominant U.S. driver. But the planet is a coupled system, and two major climate patterns peaking at the same time is not a footnote.
The July 9 CPC Diagnostic Discussion will be the next scheduled update on the Pacific side. On the Indian Ocean side, the Australian Bureau of Meteorology publishes IOD status monthly. Both are worth reading side by side.
Data sources: WMO Global Seasonal Climate Update (June 2026); WMO El Niño/La Niña Update (June 2026); Climate Impact Company IOD Outlook (March 2026); India Meteorological Department monsoon forecast (April 2026); IGAD Climate Prediction and Applications Centre (ICPAC) Horn of Africa outlook; IRI ENSO Quick Look (June 2026); NOAA CPC ENSO Diagnostic Discussion (June 11, 2026).
Editorial note: This post was researched and written by Christopher W. Corwin with AI writing assistance. All data points were verified against cited primary sources prior to publication. IAMElNino.com is an independent monitoring site and is not affiliated with NOAA, WMO, or any government agency.