August 2026 ENSO Discussion

August 2026 ENSO Discussion

ENSO Current State: Ocean–Atmosphere Overview

The 2026 El Niño event continues to intensify across the central-eastern equatorial Pacific. The traditional Niño 3.4 index shows a clear and sustained increase, with the most recent seasonal mean reaching +1.51 °C during May–July 2026 and the July monthly value increasing to +2.03 °C. The latest weekly Niño 3.4 index, centered on August 12, 2026, reached +2.7 °C. Together, these observations indicate that El Niño is strengthening further and evolving toward a very strong event.

Oceanic and atmospheric indicators are becoming increasingly aligned, providing stronger evidence that the ongoing El Niño event will continue to intensify. On the atmospheric side, the Southern Oscillation Index (SOI) reached −29.1 in July 2026, while the latest 30-day SOI value, through August 17, remained strongly negative at −18.6. These persistently negative SOI values indicate a weakening of the Walker circulation, consistent with continued El Niño development. In addition, the Equatorial SOI reached −2.3 in July 2026, further indicating that the atmosphere is responding to the warming Pacific Ocean. This provides evidence that ocean–atmosphere coupling associated with El Niño is becoming increasingly established. During 8 July–6 August 2026, pronounced low-level (850-hPa) westerly wind anomalies extended across the western to east-central equatorial Pacific, while easterly anomalies dominated the eastern Pacific. This pattern is consistent with a weakening of the trade winds and continued strengthening of the El Niño circulation. Consistent with the atmospheric response to the strengthening El Niño, below-average outgoing longwave radiation (OLR)—indicating enhanced convection and precipitation—was observed along the equator near the Date Line and across the east-central equatorial Pacific Ocean. In contrast, above-average OLR, indicating suppressed convection and precipitation, persisted over the Philippines, Indonesia, and Papua New Guinea.

Further evidence of El Niño’s strengthening comes from the subsurface ocean. A pronounced reservoir of anomalous heat has developed across the central–eastern equatorial Pacific, with temperatures at depths of approximately 50–150 m between 150°W and 80°W exceeding climatological values by more than 8 °C in some areas. This substantially increased subsurface heat content provides a strong source of energy for continued surface warming and further El Niño intensification, particularly if favorable ocean–atmosphere coupling persists. The magnitude of this subsurface warming is exceptional, raising the potential for a further increase in surface temperature anomalies during the boreal fall and early winter. If this evolution continues, the 2026 El Niño could emerge as one of the strongest events in the historical ENSO record.

ENSO Strength

Forecasts of ENSO strength are estimated through a consensus-based model counting approach using a set of Niño 3.4 sea surface temperature anomaly thresholds, to indicate weak, moderate, strong and very strong El Nino and La Nina categories.

The mid-August 2026 intensity assessment provides a striking indication of the exceptional strength of the ongoing El Niño event. The model ensemble points to a remarkably strong 2026 El Niño, with the vast majority of models forecasting a “very strong” El Niño (Niño 3.4 ≥ +2.0 °C) from ASO 2026 through DJF 2026–27. The signal peaks in OND 2026, when 25 of 26 models place Niño 3.4 in the very strong category, compared with 23 of 26 models in ASO, SON, and NDJ. OND 2026 is truly off the charts: although our current intensity classification stops at +2.0 °C, 15 models forecast Niño 3.4 SST anomalies reaching or exceeding +3.0 °C—well beyond our highest defined intensity category. Importantly, this is not simply a high-probability El Niño; the ensemble shows an unusually strong and consistent signal for an event of exceptional intensity. Even as the ensemble shifts toward weaker categories in early 2027, the persistence of strong-to-moderate El Niño conditions through MAM 2027 underscores the unusual magnitude and durability of the 2026 event. Taken together, the mid-August objective ENSO outlook points to a sustained, exceptionally strong El Niño, with little indication of a transition away from El Niño before spring 2027.

Notes:

The SST anomalies cited below are based on the NOAA Optimum Interpolation Sea Surface Temperature (OISSTv2)dataset. The climatology period is 1991–2020.

The primary metric used to monitor the El Niño–Southern Oscillation (ENSO) is the traditional Niño3.4 index (TONI), defined as the area-averaged sea surface temperature anomaly over the Niño3.4 region (5°S–5°N, 170°W–120°W).

According to the CCSR/IRI definition, El Niño conditions occur when monthly TONI exceeds +0.5 °C, while La Niña conditions occur when monthly TONI falls below −0.5 °C.

An ENSO “event” is considered established when the TONI threshold (±0.5 °C) persists for at least five consecutive overlapping 3-month seasons (e.g., SON, OND, NDJ, DJF, JFM).