DIAGNOSTIC DISCUSSION
issued by
CLIMATE PREDICTION CENTER/NCEP/NWS
and the International Research Institute for Climate and Society
13 August 2015
ENSO Alert System Status: El Niño Advisory
Synopsis: There is a greater than 90% chance that El Niño will continue through Northern Hemisphere winter 2015-16, and around an 85% chance it will last into early spring 2016.
During July, sea surface temperatures (SST) anomalies were near +1.0oC in the central equatorial Pacific Ocean, and in excess of +2.0oC across the eastern Pacific (Fig. 1). SST anomalies increased in the Niño-3 and Niño-3.4 regions, while the Niño-4 and Niño-1+2 indices decreased slightly during the month (Fig. 2). Positive subsurface temperature anomalies strengthened in the central and east-central equatorial Pacific during the month (Fig. 3), in association with the eastward movement of a downwelling oceanic Kelvin wave (Fig. 4). The atmosphere remained coupled to the oceanic warming, with significant low-level westerly wind anomalies continuing from the western to east-central equatorial Pacific, along with anomalous upper-level easterly winds. Also, the traditional and equatorial Southern Oscillation Index (SOI) were both negative, consistent with enhanced convection over the central and eastern equatorial Pacific and suppressed convection over Indonesia (Fig. 5). Collectively, these atmospheric and oceanic features reflect a significant and strengthening El Niño.
All models surveyed predict El Niño to continue into the Northern Hemisphere spring 2016, and all multi-model averages predict a strong event at its peak in late fall/early winter (3-month values of the Niño-3.4 index of +1.5oC or greater; Fig. 6). At this time, the forecaster consensus unanimously favors a strong El Niño, with peak 3-month SST departures in the Niño 3.4 region potentially near or exceeding +2.0oC. Overall, there is a greater than 90% chance that El Niño will continue through Northern Hemisphere winter 2015-16, and around an 85% chance it will last into early spring 2016 (click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).
Across the contiguous United States, temperature and precipitation impacts associated with El Niño are expected to remain minimal during the remainder of the Northern Hemisphere summer and increase into the late fall and winter (the 3-month seasonal outlook will be updated on Thursday August 20th). El Niño will likely contribute to a below normal Atlantic hurricane season, and to above-normal hurricane seasons in both the central and eastern Pacific hurricane basins.
