During May, ENSO-neutral continued, though sea surface temperatures (SSTs) were above average in the east-central Pacific Ocean [Fig. 1]. The latest weekly Niño index values were near +0.5°C in most of the Niño regions, except for the easternmost Niño-1+2, which was at +0.2°C [Fig. 2]. The upper-ocean heat content anomaly increased during May [Fig. 3], reflecting the expansion of above-average sub-surface temperatures across the central and eastern Pacific [Fig. 4] in association with a downwelling oceanic Kelvin wave. While ocean temperatures were elevated, the atmosphere was close to average. Atmospheric convection anomalies were weak over the central tropical Pacific and Maritime Continent [Fig. 5], while the lower-level and upper-level winds were near average over most of the tropical Pacific. Both the Southern Oscillation Index (SOI) and Equatorial SOI were also near zero. Overall, the ocean and atmosphere system remains consistent with ENSO-neutral.
Many models predict the onset of El Niño (3-month average Niño-3.4 index at or greater than 0.5°C) during the Northern Hemisphere summer [Fig. 6]. However, the NCEP CFSv2 and most of the models from the latest runs of the North American Multi-Model Ensemble (NMME) are now favoring the continuation of ENSO-neutral. These predictions, combined with the near-average atmospheric conditions over the Pacific, have resulted in slightly more confidence for the persistence of ENSO-neutral (50 to ~55% chance). However, chances for El Niño remain elevated (35-50%) relative to the long-term average into the fall. In summary, ENSO-neutral is favored (50 to ~55% chance) through the Northern Hemisphere fall 2017 (click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).
This discussion is a consolidated effort of the National Oceanic and Atmospheric Administration (NOAA), NOAA's National Weather Service, and their funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center web site (El Niño/La Niña Current Conditions and Expert Discussions). Forecasts are also updated monthly in the Forecast Forum of CPC's Climate Diagnostics Bulletin. Additional perspectives and analysis are also available in an ENSO blog. The next ENSO Diagnostics Discussion is scheduled for 13 July 2017. To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send an e-mail message to: firstname.lastname@example.org.