El Niño Status and Forecast

ENSO-neutral conditions prevail in the tropical Pacific Ocean, but forecast models continue to favor the development of an El Niño later this year. Sea surface temperatures (SSTs), which had been warming in recent months, leveled during the last 30 days but remain near average across most of the eastern equatorial Pacific Ocean. This indicates that ENSO-neutral conditions currently dominate the Pacific Ocean basin, closing the door on the La Niña event of this past winter. This shift back towards average conditions is reflected in the May value of the Southern Oscillation Index (SOI), which returned to near zero (Figure 14a).

Last month, a large pool of warmer-than-average water flowed just below the surface across much of the eastern equatorial Pacific Ocean. Forecasters and forecast models expected this warm water to make its way to the surface sometime within a few months, bringing on weak El Niño conditions as early as this fall. While forecast models continued to favor the development of an El Niño event this month, they now depict the possibility of a slower onset of El Niño. Official forecasts issued jointly by the NOAA-Climate Prediction Center (CPC) and International Research Institute for Climate and Society (IRI) show a near 50–50 split between neutral conditions and El Niño conditions for the July–September period, with chances for the development of El Niño rising thereafter (Figure 14b). If and when El Niño develops, the current expectations are that it will be weak and may not heavily influence weather conditions in fall and winter. This forecast, however, will continue to evolve as the summer progresses.