February 2026 IOD Discussion

February 2026 IOD Discussion

Note: The Dipole Mode Index is calculated based on the ERSSTv5 data. To account for evolving background conditions and long-term warming, SST anomalies were calculated relative to a sliding monthly climatology. For each month in the time series, the climatology was computed as the mean SST for that calendar month over the prior 30 years. The Dipole Mode Index (DMI) is then defined as the difference in sea surface temperature anomalies between the western equatorial Indian Ocean (50°E–70°E, 10°S–10°N) and the southeastern equatorial Indian Ocean (90°E–110°E, 10°S–0°), and is used to quantify the strength and phase of the Indian Ocean Dipole (IOD).

Current Conditions

In Jan 2026, the observed Dipole Mode Index was near zero, indicating neutral IOD conditions across the Indian Ocean. According to the CCSR@NASA-GISS/IRI’s criteria for defining positive and negative Indian Ocean Dipole (IOD) events, a positive IOD phase is defined when the DMI exceeds +0.4 °C, and a negative IOD when it falls below −0.4 °C. The IOD is considered inactive (neutral) when the DMI lies between −0.4 °C and +0.4 °C.

Model-Based IOD Outlook: Deterministic Forecasts from the NMME

Forecasts from the latest set of operational models in the North American Multi-Model Ensemble (NMME) project are used to construct deterministic IOD forecasts from each individual model using its ensemble mean DMI to form an IOD forecast plume. The IOD plume plot shows the latest set of predictions from CESM1, CFSv2, CanESM5, GEM-NEMO, and NASA along with their equally weighted multi-model mean (MME). The observed DMI (shown in black) rose steadily from its negative-phase peak in October 2025, gradually weakening through the end of 2025 and returning to neutral IOD conditions by January 2026. Forecasts for February 2026 show that in February and March two models, NASA and GEM-NEMO, indicate DMI values exceeding the +0.4°C threshold, while the remaining models remain within the neutral range. However, the MME overall favors IOD-neutral conditions (DMI between −0.4°C and +0.4°C) for these months. Looking further ahead, most models show a gradual increase in DMI values, particularly beyond May 2026. By August 2026, the MME mean points toward the development of positive IOD conditions.

Probabilistic IOD Forecasts from the NMME

Based on February 2026 initialization data, the model-based probabilistic forecast of the Indian Ocean Dipole was generated by CCSR@NASA-GISS/IRI to assess potential phase developments. Probabilities are computed using an ensemble-member counting method, where all ensemble members from the contributing models (92 in this case), and pooled to determine the likelihood of a negative, neutral, or positive IOD phase for the upcoming months. Climatological probabilities for each IOD phase, based on historical data, are shown as dotted lines for reference. Throughout the February–June 2026 period, IOD-neutral conditions remain the most likely state, with the main shift being a gradual rise in the probability of a positive IOD. By July, positive IOD and neutral conditions are equally likely, each with a 47% chance. In August 2026, the likelihood of a positive IOD increases to 56%, while neutral conditions drop to 37%; the probability of a negative IOD remains below 10%.

In summary, February 2026 favors IOD-neutral conditions, which continue to dominate through the outlook period, while positive IOD emerges as the next most probable scenario.