El Niño Status and Forecast

The march towards a possible El Niño event slowed this past month as sea surface temperatures (SSTs) held steady and even cooled in some areas across the equatorial Pacific Ocean. An El Niño Watch issued several months ago by the NOAA-Climate Prediction Center (CPC) remains in effect this month, meaning that El Niño conditions may still develop in the next several months. Mixed signals across the equatorial Pacific Ocean include a slight cooling of SSTs and weak atmospheric circulation pattern shifts—the Southern Oscillation Index is only slightly negative (Figure 12a)—but widespread warmer-than-average water just below the surface indicates the steady progression towards the El Niño event observed over the past several months has slowed.

Official forecasts issued jointly by the CPC and the International Research Institute for Climate and Society (IRI) still depict a strong chance (82 percent) that El Niño conditions will develop sometime in the September–November period (Figure 12b). This is up slightly from the 78 percent chance forecast last month for the same time period. The chance of El Niño conditions developing is quite high relative to the chance of current neutral conditions persisting (18 percent). Regardless, the event is forecast to be  weak at best and is expected to quickly wane in the late winter season. The CPC notes that this may limit the impact that El Niño conditions have on the upcoming winter circulation. A weaker forecast of above-average winter precipitation across the Southwest that is limited to far southern portions of Arizona and New Mexico. Conditions in the Pacific Ocean will continue to change over the next 30 days, and forecasts will continue to be adjusted; confidence in the ultimate fate of the El Niño event will grow in coming months.