Experimental Seasonal ENSO Forecasts

The June experimental predictions produced by SPEAR indicate a high probability of a very strong El Niño by fall. Compared with last month, the uncertainty of the strength due to chaotic weather variability is reduced, as shown by the reduced model spread (the differences between the individual purple lines). This month, all 30 ensemble members (dotted purple lines) have a peak relative Niño-3.4 index above 2 °C next fall or early winter, values that generally are only reached every one to two decades. This level of agreement among ensemble members indicate high confidence in a strong El Niño.

The figure shows the latest experimental seasonal predictions of the El Niño-Southern Oscillation (ENSO) from the GFDL SPEAR prediction system. The predictions (purple lines) started on June 1, 2026 and extend through May 31, 2027 (x-axis). The y-axis indicates the strength of El Niño or La Niña, with more positive values indicating a stronger El Niño (warmer water in the east-central tropical Pacific relative to the tropical average temperature). The individual lines represent different forecast realizations starting from slightly different initial states, representing the forecast uncertainty from chaotic climate variability. The thick solid lines represent the average of all realizations, showing the forecast signal after filtering out the influence of chaotic climate variability. The green lines represent the predictions from the previous month, illustrating how much the forecast has changed.

For a comparison with other experimental ENSO predictions from the North American Multi-Model Ensemble (NMME), click here, and for latest NOAA ENSO Outlook, click here. Additional information on ENSO, including impacts, can be found here.

The latest experimental predictions continue to indicate a likely transition to El Niño conditions by summer and the high probability of a strong El Niño by fall. However, the large model spread (the differences between the individual purple lines) indicates that there still is considerable uncertainty in the precise strength of the El Niño predicted by SPEAR due to the influence of chaotic weather variability.

The figure shows the latest experimental seasonal predictions of the El Niño-Southern Oscillation (ENSO) from the GFDL SPEAR prediction system. The predictions (purple lines) started on May 1, 2026 and extend through April 30, 2027 (x-axis). The y-axis indicates the strength of El Niño or La Niña, with more positive values indicating a stronger El Niño (warmer water in the east-central tropical Pacific relative to the tropical average temperature). The individual lines represent different forecast realizations starting from slightly different initial states, representing the forecast uncertainty from chaotic climate variability. The thick solid lines represent the average of all realizations, showing the forecast signal after filtering out the influence of chaotic climate variability. The green lines represent the predictions from the previous month, illustrating how much the forecast has changed. For a comparison with other experimental ENSO predictions from the North American Multi-Model Ensemble (NMME), click here, and for latest NOAA ENSO Outlook, click here. Additional information on ENSO, including impacts, can be found here.

The latest experimental predictions indicate an elevated probability of a transition to El Niño conditions by summer and continued El Niño strengthening through early winter. Although chaotic climate variability (the spread of the individual lines) limits confidence in the strength of the predicted El Niño, the SPEAR predictions indicate an unusually high likelihood of a moderate-to-strong El Niño by fall.

The figure shows the latest experimental seasonal predictions of the El Niño-Southern Oscillation (ENSO) from the GFDL SPEAR prediction system. The predictions (purple lines) started on April 1, 2026 and extend through March 31, 2027 (x-axis). The y-axis indicates the strength of El Niño or La Niña, with more positive values indicating a stronger El Niño (warmer water in the east-central tropical Pacific relative to the tropical average temperature). The individual lines represent different forecast realizations starting from slightly different initial states, representing the forecast uncertainty from chaotic climate variability. The thick solid lines represent the average of all realizations, showing the forecast signal after filtering out the influence of chaotic climate variability. The green lines represent the predictions from the previous month, illustrating how much the forecast has changed. For a comparison with other experimental ENSO predictions from the North American Multi-Model Ensemble (NMME), click here, and for latest NOAA ENSO Outlook, click here. Additional information on ENSO, including impacts, can be found here.