El Niño Status and Forecast

Near-average sea surface temperatures (SSTs) reigned across the equatorial Pacific Ocean again this past month, reflecting ENSO-neutral conditions. Values of the Southern Oscillation Index (SOI), which tracks the atmospheric response to ENSO events, also dropped close to zero last month after peaking at record high values in April and May (Figure 14a). This also reflects a return to neutral conditions. There are some weak and lingering remnants of the La Niña event in the atmosphere, but they are having little impact on overall atmospheric circulation patterns, according to the NOAA-Climate Prediction Center (CPC).

Forecasts issued by the International Research Institute for Climate and Society (IRI) indicate a strong chance—greater than 80 percent—that neutral conditions will persist through the summer. This decreases in the fall to about 60 percent, while the chance that El Niño or La Niña will develop is 14 and 26 percent, respectively (Figure 14b). However, the combination of a weak but lingering La Niña pattern in the atmosphere and the emergence of slightly cooler-than-average water temperatures below the surface in the eastern Pacific suggest a possible return of La Niña conditions in the upcoming fall or winter. Most forecast models still paint the return of La Niña as an unlikely outcome, but the area of cool subsurface water will be monitored closely over the next several months. The return of La Niña conditions could be bad news for an already parched Southwest battered by a record dry winter and spring. La Niña events have a strong tendency to drive the winter storm track north and away from Arizona and New Mexico, as was the case this past winter.