We’d like our forecasts—both weather and climate—to be simple and certain. Because of the fluid and chaotic nature of the ocean and atmosphere, however, forecasts are never about certainty: they’re about probability.
Chances that an El Niño will occur by summer are above 70%, hitting 80% by the fall. But subsurface temperature anomalies have tapered off some from earlier this spring, decreasing the odds the event will be as strong as the El Niño of 1997-98.
The forecast models are largely in agreement that SSTs will continue to trend upward, with the majority of models indicating a Niño3.4 index value above 0.5°C by early summer. Forecast show the chance of El Niño increasing during the remainder of the year, exceeding 65% during the summer.
Though ENSO is a single climate phenomenon, it has three states, or phases, it can be in. The two opposite phases, “El Niño” and “La Niña,” require certain changes in both the ocean and the atmosphere because ENSO is a coupled climate phenomenon. “Neutral” is in the middle of the continuum.