Warm episode (El Niño) conditions continued during January 2003, as equatorial SST anomalies remained greater than +1°C in the central equatorial Pacific (175°E-125°W, Fig. 1). In addition, enhanced precipitation and cloudiness were observed over the central tropical Pacific (Fig. 2), and positive subsurface temperature departures (Fig. 3) and a deeper-than-average oceanic thermocline were observed throughout the equatorial Pacific east of 180°W. These conditions are consistent with mature warm episode conditions.

During January 2003 there were indications that the warm episode is beginning to weaken. Sea-surface temperature anomalies decreased throughout the eastern equatorial Pacific by as much as 1.5°C during the month (Fig. 4), while equatorial easterly winds were near normal throughout the central and eastern equatorial Pacific. Over the past several weeks there has also been a steady eastward progression of negative subsurface temperature anomalies, indicating a gradual depletion of the excess warmth in the upper ocean of the equatorial Pacific. This evolution is typical during the mature phase of warm episodes.

Recent values of atmospheric and oceanic indices, such as the SOI, 850-hPa zonal wind index, Niño 3.4, Niño 3, Niño 1+2 are all considerably smaller in magnitude than those observed during the 1997-98 El Niño (Fig. 5). The warming associated with the current event has been greatest in the central equatorial Pacific (Niño 4 and Niño 3.4 regions). Regions farther east (e.g., Niño 3 and especially Niño 1+2) have warmed much less. A comparison with previous warm episodes in the last 50 years (Fig. 6) indicates that, for the equatorial Pacific as a whole, the current event is moderate in intensity.

Consistent with current conditions and recent observed trends, most coupled model and statistical model forecasts indicate that El Niño conditions will continue to weaken through April 2003. Thereafter, the consensus forecast is for near-normal conditions during May-October 2003. Those areas of the world usually affected by El Niño may continue to experience related impacts during the next 2-3 months.

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 updated ENSO Diagnostic Discussions are released please send your e-mail address to: