Sea surface temperature (SST) anomalies were between 1.0° and 1.5°C across most of the central and eastern equatorial Pacific Ocean during early April (Fig. 1), having weakened appreciably over the last month. The latest weekly values for all of the Niño indices dropped to below 1.5°C (Fig. 2). The subsurface temperature anomaly in the central and eastern Pacific decreased to negative values (Fig. 3) in association with a significant expansion of below-average temperatures at depth (Fig. 4). Low-level westerly wind anomalies and upper-level easterly wind anomalies weakened compared to February. The equatorial Southern Oscillation Index (SOI) remained negative but weakened, while the traditional SOI was near zero. Enhanced convection continued over the central tropical Pacific but weakened east of the Date Line, and was suppressed over northern Indonesia and the Philippines (Fig. 5). Collectively, these anomalies reflect a weakening El Niño.
Nearly all models predict further weakening of El Niño, with a transition to ENSO-neutral likely during late spring or early summer 2016 (Fig. 6). Then, the chance of La Niña increases during the late summer or early fall. The official forecast is consistent with the model forecasts, also supported by a historical tendency for La Niña to follow strong El Niño events. A transition to ENSO-neutral is likely during late Northern Hemisphere spring or early summer 2016, with an increasing chance of La Niña during the second half of the year.
