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August

Seasonal ENSO Forecast

El Niño conditions are currently intensifying across the tropical Pacific, with SST anomalies in the Niño3.4 region (5°S–5°N, 120°–170°W) showing a steady upward trend. The observed SST anomaly reached 2.1°C in July 2026, placing a very strong El Niño level, consistent with our previous XRO forecast from May-July 2026. Our XRO forecast Niño3.4 anomalies exceeding +3.5°C by Oct 2026, reaching peak 4.3°C by Nov-Dec 2026, providing a high level of confidence of an unprecedented super El Niño event since 1950 characterized by significant warming in the central and eastern tropical Pacific (Figure 1).

Fig 1

Figure 1. Seasonal ENSO forecasts based on the Niño3.4 sea surface temperature (SST) anomalies (120-170W, 5S-5N, °C) from August 2026 using the XRO (blue).

Hawaii Wave Seasonal Outlook

The development of a super El Niño is expected to substantially modulate significant wave height (SWH) around the Hawaiian Islands over the coming seasons. Figures 2 and 3 show forecasts of seasonally mean and 90th-percentile SWH anomalies, respectively, from July-September (JAS) 2026 through early March-May (MAM) 2027. Positive SWH anomalies, indicative of enhanced wave activity, are already emerging along north- and northwest-facing shores in JAS 2026. These seasonal anomalies are expected to intensify progressively through boreal fall and winter as El Niño matures. The largest positive anomalies could exceed +0.4 m in mean SWH and +0.7 m in the 90th percentile for NDJ 2026 through JFM 2027.

The projected increase in wave heights around Hawaii is consistent with a strengthened North Pacific jet stream, an equatorward-shift of the storm track, and enhanced high-latitude swell generation, all of which are characteristics of strong El Niño winters (Stopa & Cheung, 2014; Zhao et al. 2025). In contrast, outlooks for south- and southeast-facing shores indicate weaker or near-neutral anomalies throughout the forecast period, although the forecast skill in these regions is comparatively lower.

Fig 2

Figure 2. Seasonal mean significant wave height anomaly outlook issued in August 2026 from the XROWaveModel. Hatched areas denote regions where the corresponding hindcast anomaly correlation coefficient (ACC) evaluated over the 1980–2024 period, is below 0.5, suggesting reduced forecast skill and lower confidence in the predicted anomalies.

Fig 3

Figure 3. Outlook of seasonal 90th percentile significant wave height anomalies (m) issued in August 2026 from the XROWaveModel. Hatched areas denote regions where the corresponding hindcast anomaly correlation coefficient (ACC) evaluated over the 1980–2024 period, is below 0.5, suggesting reduced forecast skill and lower confidence in the predicted anomalies.