Warm episode (El Niño) conditions continued to weaken during March 2003, as the equatorial easterlies strengthened and SST anomalies decreased throughout the eastern and central equatorial Pacific. Since December, SST anomalies have decreased by more than 2°C in the eastern equatorial Pacific between 130°W and the South American coast (Fig. 1). This decrease has resulted in near normal or slightly below normal SSTs in the region east of 120°W since February. During the same period there has also been a steady decrease in the magnitude and extent of the positive subsurface temperature anomalies, indicating a depletion of the excess warmth in the upper ocean of the equatorial Pacific (Fig. 2). This evolution is typical during the decay phases of warm episodes.

In spite of these trends, significant positive SST anomalies remained in the central equatorial Pacific during March 2003, with anomalies greater than +1°C extending from 170°E to 140°W (Fig. 1, middle panel). Greater-than-average precipitation and cloudiness were found over the western portion of this region, although the departures from average and the spatial coverage have decreased substantially during the last two months (Fig. 3). The Tahiti-Darwin SOI remained negative (-1.0) for the 13th consecutive month, while the equatorial SOI was near zero.

A comparison of the 2002-03 El Niño episode with previous events in the last 50 years (Fig. 4) indicates that for the equatorial Pacific as a whole the 2002-2003 event was moderate in intensity. The SST departures associated with the event were greatest in the central equatorial Pacific (Niño 4 and Niño 3.4 regions) and least in the eastern equatorial Pacific (e.g., Niño 3 and especially Niño 1+2). This pattern of anomalous warming, combined with the rapid weakening of the event, had a generally weaker than expected influence on the atmospheric circulation and hence the precipitation and temperature patterns over North and South America during January - March 2003.

Consistent with current conditions and recent observed trends, a majority of the coupled model and statistical model forecasts indicate that near-normal conditions will prevail through September 2003. However, there is uncertainty in this forecast as some forecasts indicate the possibility of continued weak El Niño conditions while others indicate the development of La Niña conditions during the second half of 2003.

This discussion is a consolidated effort of NOAA and its funded institutions. Weekly updates for SST, 850-hPa wind, OLR and features of the equatorial subsurface temperature structure are available on the Climate Prediction Center web page at http://www.cpc.ncep.noaa.gov (Weekly Update). Forecasts for the evolution of El Niño/La Niña are updated monthly in CPC's Climate Diagnostics Bulletin Forecast Forum. To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send your e-mail address to: