EL NI?O/SOUTHERN OSCILLATION (ENSO)
DIAGNOSTIC DISCUSSION
issued by
CLIMATE PREDICTION CENTER/NCEP/NWS
and the International Research Institute for Climate and Society
6 November 2014
ENSO Alert System Status: El Ni?o Watch
Synopsis: There is a 58% chance of El Ni?o during the Northern Hemisphere winter, which is favored to last into the Northern Hemisphere spring 2015.
During October 2014, above-average sea surface temperatures (SST) increased slightly across the eastern half of the equatorial Pacific (Fig. 1). The weekly Ni?o indices were between +0.6oC (Ni?o-3.4 and Ni?o-1+2) and +0.9oC (Ni?o-3) at the end of the month (Fig. 2). Subsurface heat content anomalies (averaged between 180o-100oW) were largely unchanged (Fig. 3) even as a new downwelling Kelvin wave increased temperatures at depth in the central Pacific (Fig. 4). The monthly equatorial low-level winds were near average, although anomalous westerlies continued to emerge on occasion. Upper-level winds were also mostly average across the Pacific. The Southern Oscillation Index continued to be negative, accompanied by mostly average rainfall near the Date Line and suppressed rainfall over Indonesia (Fig. 5). Overall, several features across the tropical Pacific are characteristic of borderline El Ni?o conditions, but collectively, the combined atmosphere and oceanic state remains ENSO-neutral.
Similar to last month, most models predict El Ni?o to develop during October-December 2014 and to continue into early 2015 (Fig. 6). However, the ongoing lack of clear atmosphere-ocean coupling and the latest NCEP CFSv2 model forecast (Fig. 7) have reduced confidence that El Ni?o will fully materialize (at least five overlapping consecutive 3-month values of the Ni?o-3.4 index at or greater than 0.5oC). If El Ni?o does emerge, the forecaster consensus favors a weak event. In summary, there is a 58% chance of El Ni?o during the Northern Hemisphere winter, which is favored to last into the Northern Hemisphere spring 2015 (click CPC/IRI consensus forecast for the chance of each outcome)...
