10 April 2014
Synopsis: While ENSO-neutral is favored for Northern Hemisphere spring, the chances of El Niño increase during the remainder of the year, exceeding 50% by summer.
ENSO-neutral continued during March 2014, but with above-average sea surface temperatures (SST) developing over much of the eastern tropical Pacific as well as near the International Date Line (Fig. 1). The weekly SSTs were below average in the Niño1+2 region, near average but rising in Niño3 and Niño3.4 regions, and above average in the Niño4 region (Fig. 2). A significant downwelling oceanic Kelvin wave that was initiated in January greatly increased the oceanic heat content to the largest March value in the historical record back to 1979 (Fig. 3) and produced large positive subsurface temperature anomalies across the central and eastern Pacific (Fig. 4). Also during March, low-level westerly wind anomalies were observed over the central equatorial Pacific. Convection was suppressed over western Indonesia, and enhanced over the central equatorial Pacific (Fig. 5). Although these atmospheric and oceanic conditions collectively reflect ENSO-neutral, they also reflect a clear evolution toward an El Niño state.
The model predictions of ENSO for this summer and beyond are indicating an increased likelihood of El Niño this year compared with last month. Most of the models indicate that ENSO-neutral (Niño-3.4 index between -0.5oC and 0.5oC) will persist through much of the remainder of the Northern Hemisphere spring 2014 (Fig. 6), with many models predicting the development of El Niño sometime during the summer or fall. Despite this greater model consensus, there remains considerable uncertainty as to when El Niño will develop and how strong it may become. This uncertainty is amplified by the inherently lower forecast skill of the models for forecasts made in the spring. While ENSO-neutral is favored for Northern Hemisphere spring, the chances of El Niño increase during the remainder of the year, and exceed 50% by the summer (click CPC/IRI consensus forecast for the chance of each outcome).
