El Niño Tracker - May 2016

El Niño conditions continued for a 15th straight month, but the peak intensity has long since passed and the event is moving toward ENSO-neutral status. Forecast discussions focused on the decline of atmospheric and oceanic anomalies that characterize an El Niño event, many of which are trending towards—or have nearly reached—ENSO-neutral status. Seasonal ENSO outlooks and forecasts have coalesced around the likely transition to La Niña conditions in fall or winter 2016. The spring predictability barrier—a time during seasonal transition that introduces a high degree of uncertainty into seasonal forecast models—makes identifying the exact timing of this transition difficult, but most models and forecasts center on the general framing of “Not if, but when?” regarding La Niña in 2016.

On May 10, the Australian Bureau of Meteorology maintained its outlook at La Niña Watch status, noting that El Niño conditions had weakened to borderline neutral status and that there was a 50 percent probability of a La Niña event developing in 2016. On May 12, the Japan Meteorological Agency identified a decaying El Niño event that is expected to weaken to neutral conditions by late spring followed by a developing La Niña by summer 2016. On May 12, the NOAA-Climate Prediction Center (CPC) extended its El Niño Advisory and its La Niña Watch. The CPC identified current atmospheric anomalies as reflecting an ongoing but declining El Niño event, while oceanic anomalies were much more indicative of ENSO-neutral status. The CPC forecast an end to El Niño by early summer (i.e., a return to neutral conditions), with a 75 percent probability of a transition to La Niña in fall or winter 2016. On May 19, the International Research Institute for Climate and Society (IRI) and CPC forecasts described a rapidly declining El Niño event, with La Niña conditions more than likely developing by late summer (Fig. 3). The North American multi-model ensemble shows the current decline from strong to moderate El Niño status over the past few months, as well as the possibility of a relatively rapid swing to weak to moderate La Niña conditions by summer (Fig. 4).