Indian Ocean Dipole - IOD Tracker
The Indian Ocean Dipole is the Indian Ocean’s own coupled ocean-atmosphere mode - a sea-surface temperature seesaw between the western and southeastern equatorial Indian Ocean that shifts flood and drought risk between East Africa and Indonesia/Australia. It has real impacts independent of ENSO, and an actively-researched interaction with it - and even with the North Atlantic Oscillation. This page combines BOM’s weekly Dipole Mode Index for the current state with NOAA’s 150-year monthly history and today’s regional impacts.
Current State - Neutral
The Indian Ocean Dipole is the sea-surface temperature seesaw between the western and southeastern equatorial Indian Ocean. The figure below combines BOM's weekly DMI reading (days behind, not months) with NOAA PSL's long monthly record for history and cross-check.
Equatorial Indian Ocean
Orange glow = relatively warmer, blue glow = relatively cooler for the current phase - each hugs the coast where the actual upwelling/downwelling happens. Blue tags = wetter, orange tags = drier; arrows show the equatorial surface-wind anomaly (west = weakened/reversed westerlies, east = normal/intensified westerlies). The DMI is one differenced value (west minus east SST anomaly), so all of this is qualitative, from the sign of the current DMI +0.22°C alone, not an independent per-region reading.
IOD phase - current week
Neutral
+0.22°C · week to 2026-08-30
no strong signal either way
ENSO state, for context
El Niño (Moderate)
RONI +1.36 · JJA 2026
NOAA PSL monthly (long-record cross-check)
+0.15°C · May 2026 - annual mean -0.13°C - HadISST1.1 typically runs 3-4 months behind the present, which is why the current-state figure above leads with BOM's fresher weekly reading instead.
IOD and ENSO relationship right now
ENSO is currently El Niño, but with the IOD itself neutral, the Indian Ocean isn't adding an independent signal right now.
Thresholds: ≥ +0.4°C Positive · ≤ -0.4°C Negative · otherwise Neutral (the BOM/NOAA CPC convention). Data: BOM weekly DMI · NOAA PSL DMI monthly series (HadISST1.1).
History (1870-present)
IOD History
BOM's weekly Dipole Mode Index shows the last few years in detail; NOAA PSL's annual mean shows the full 1870-present record. Amber shading marks positive-IOD (East Africa wet / Indonesia-Australia dry); cyan shading marks negative-IOD (the reverse).
The top chart is BOM’s weekly DMI - the freshest available reading, days behind rather than months. The bottom chart is NOAA PSL’s annual mean DMI back to 1870 (HadISST1.1); dashed gold verticals mark the two most consequential recent positive-IOD events on record. PSL’s underlying monthly series currently publishes through May 2026. Data: BOM weekly DMI · NOAA PSL DMI monthly series (HadISST1.1).
Regional Impacts
Where Does the IOD Bite Hardest?
The IOD's footprint spans the Indian Ocean rim. Below is the canonical pattern for each phase, with today's live regime highlighted at the top.
Live: Neutral IOD today
With the DMI inside ±0.4°C, neither the +IOD nor -IOD pattern is being reinforced. Regional rainfall in East Africa, Indonesia and Australia is driven more by ENSO and other factors than by the Indian Ocean alone right now.
Positive IOD (+IOD)
- East Africa (Kenya, Somalia, Ethiopia, Tanzania)
Wetter · flood risk - Warmer western Indian Ocean feeds more moisture into the short-rains season; the extreme 2019 positive IOD co-occurred with catastrophic East African flooding. - Indonesia, Malaysia, Maritime Continent
Drier · wildfire/haze risk - Suppressed convection over the cooler eastern Indian Ocean weakens the monsoon trough, raising peatland/forest fire risk. - Australia (especially SE)
Drier · elevated bushfire risk - Reduced moisture transport into the Australian monsoon; the 2019 positive IOD directly primed the record 2019-2020 "Black Summer" bushfire season. - Indian subcontinent
Can boost monsoon rainfall - A positive IOD sometimes offsets a weak-monsoon signal from El Niño, though the relationship is less consistent than the East Africa/Australia impacts.
Negative IOD (-IOD)
- East Africa (Kenya, Somalia, Ethiopia, Tanzania)
Drier · drought risk - Suppressed short-rains; negative-IOD years have contributed to some of the region’s worst droughts, including conditions around the 2010-2011 Horn of Africa famine. - Indonesia, Malaysia, Maritime Continent
Wetter - Enhanced convection over the warmer eastern Indian Ocean increases rainfall across the Maritime Continent. - Australia (especially SE)
Wetter - Increased moisture transport into the Australian monsoon and southeast Australia rainfall. - Indian subcontinent
Can weaken monsoon rainfall - A negative IOD tends to work against monsoon rainfall, particularly when it co-occurs with La Niña.
The IOD was first identified by Saji et al. (1999, Nature). Its interaction with ENSO and the North Atlantic-European circulation is documented in Raganato et al. (2024, J. Climate) and Fahad et al. (2025, Comms Earth & Environment). See the ENSO tracker for the other half of the tropical Indo-Pacific picture.
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FAQs
Indian Ocean Dipole: Common Questions
What is the Indian Ocean Dipole (IOD)?
The Indian Ocean Dipole is a coupled ocean-atmosphere climate pattern - the Indian Ocean's own equivalent of ENSO. It is measured by the Dipole Mode Index (DMI): the sea-surface temperature anomaly gradient between the western Indian Ocean (near the Horn of Africa) and the southeastern Indian Ocean (near Sumatra). A positive IOD means the west is warmer than average and the east cooler; a negative IOD is the reverse.
What does a positive IOD mean?
A positive IOD (warm west, cool east) shifts rainfall west, toward East Africa, and suppresses it in the east. It typically brings above-average rain and flood risk to Kenya, Somalia, Ethiopia and Tanzania, while Indonesia, Malaysia and Australia tend toward drought and elevated bushfire risk. The extreme positive IOD of 2019 co-occurred with catastrophic flooding in East Africa and directly primed the record-breaking 2019-2020 Australian bushfire season.
What does a negative IOD mean?
A negative IOD (cool west, warm east) reverses the pattern: rainfall shifts east, bringing wetter conditions to Indonesia and northern Australia while East Africa tends toward drought. Negative IOD years have preceded some of East Africa's worst droughts, including contributing conditions to the 2010-2011 Horn of Africa famine.
How does the IOD relate to ENSO (El Niño / La Niña)?
The IOD and ENSO are physically distinct systems in different ocean basins, but they interact and often co-occur: positive IOD events happen alongside El Niño more often than chance would predict, and recent research (2024) shows the combined IOD+ENSO signal reaches all the way to North Atlantic-European winter circulation via the same tropical wave-train pathway that links El Niño to the North Atlantic Oscillation. A 2025 modelling study found this IOD-to-North-Atlantic teleconnection is strongest when ENSO itself is inactive, and is projected to weaken further under continued climate change.
How is the IOD measured and how often does this page update?
The IOD is tracked via the Dipole Mode Index (DMI), combining two sources: the Australian Bureau of Meteorology's weekly DMI reading (days behind, not months) for the current-state figure, and NOAA PSL's HadISST1.1-based monthly DMI (1870-present) for the long history and as a cross-check. This page refreshes weekly. PSL's own monthly figure typically runs 3-4 months behind the present on its own - that's expected and is why the current-state figure leads with BOM's fresher weekly reading instead.
Is there a seasonal forecast for the IOD?
Bodies like the World Meteorological Organization publish qualitative seasonal outlooks for the IOD from coupled dynamical models, and these are worth reading directly for the current season's expectation. This site deliberately doesn't turn that kind of report into a projected line on the IOD chart, though - a hand-transcribed figure from a periodic report goes stale the moment the season passes, and a generic statistical carry-forward can just as easily contradict what a real forecast center is actually saying. Rather than show a line that might be wrong in either direction, the IOD chart shows observed history only, with no forecast dashing, until a live automated seasonal-forecast feed exists for the IOD to plot from directly.
Why does 4 Billion Years On track the IOD separately from ENSO?
The IOD has real regional impacts independent of ENSO - East African rainfall, Indonesian/Australian drought and bushfire risk, and Indian monsoon modulation are all driven by the IOD in years when ENSO itself is neutral. Because it also has a genuine, currently-researched interaction with ENSO and even the North Atlantic Oscillation, it earns its own tracker page alongside ENSO, NAO, PNA, AMV and the Stratospheric Polar Vortex on the 4byo Climate Symphony.