El Niño Status and Forecast

Sea surface temperatures (SSTs) across the equatorial Pacific Ocean continued to warm during the past 30 days, helping to reinforce the ENSO-neutral conditions that began to take hold in mid-April. The NOAA-Climate Prediction Center (CPC) reports that SSTs are currently close to average across much of the east Pacific Ocean and that the lingering La Niña-like atmospheric circulation, including enhanced easterly trade winds along the equator and enhanced convection in the western Pacific Ocean, also have started to wane. The Southern Oscillation Index (SOI) in April fell to -0.3, and the most current three-month moving average of the SOI is now at ENSO-neutral levels for the first time since last summer (Figure 15a). All of these observations indicate ENSO-neutral conditions have returned, at least for the short term.

How long neutral conditions will last is the big question. A substantial pool of water with above-average temperatures has started to accumulate just below the sea surface across much of the equatorial Pacific Ocean, and some of this warmer-than-average water already has surfaced in the far eastern Pacific. This pool has increased the prospect of an El Niño event developing as early as mid-summer, according to the latest forecast model simulations. The official ENSO forecast issued by NOAA-CPC and the International Research Institute for Climate and Society (IRI) indicates nearly a 50 percent chance of an El Niño event developing in the July–September season, matching the forecast chance of neutral conditions continuing (Figure 15b). IRI notes that several models that include information about the current state of the subsurface warm pool favor the development of El Niño conditions as early as July.

Overall, it looks like either ENSO-neutral or weak El Niño conditions will develop during the next six months. If El Niño is able to take hold and develop this fall, it could shift the upcoming fall and winter storm track to favor wetter conditions in the Southwest, providing some desperate drought relief in the region.