Warm episode (El Niño) conditions dominated the tropical Pacific during December 2002. Equatorial SST anomalies were greater than +1°C throughout most of the Pacific between the date line and the South American coast, and exceeded +2°C at several locations between 175°W and 95°W (Fig. 1). Positive subsurface temperature departures (Fig. 2) and a deeper-than-average oceanic thermocline prevailed throughout the equatorial Pacific east of 180°W. Negative subsurface temperature departures were observed west of 180°W at a depth of between 100 and 150 m. This dipole pattern in subsurface temperature anomalies is a typical feature observed during the mature phase of El Niño.

Atmospheric indicators of El Niño include consistently negative values of the Tahiti-Darwin Southern Oscillation Index (SOI) since March 2002, and weaker-than-average low-level easterly winds since May 2002 throughout the equatorial Pacific. Notable climate anomalies during October-December 2002, consistent with the ongoing El Niño, include: drier-than-average conditions over Indonesia, northern and eastern Australia, Central America and northeastern South America and wetter-than-average conditions over the central equatorial Pacific, southeastern South America and the southeastern United States (Fig. 3).

Values of atmospheric and oceanic indices, such as the SOI, 850-hPa zonal wind index, Niño 3.4, are all considerably less in magnitude than those observed during the 1997-98 El Niño (Fig. 4). Collectively, oceanic and atmospheric indices are indicative of a moderate warm (El Niño) episode.

Most coupled model and statistical model forecasts indicate that El Niño conditions will continue through the northern spring of 2003. Thereafter the forecasts are more uncertain, during a time of the year when all of the techniques have difficulty in making skillful forecasts. A critical factor governing the duration of the current warm episode is the rate of evolution of the dipole pattern in the subsurface thermal structure along the equatorial Pacific, which is linked to the persistence and eastward extension of the pattern of deep convection into the eastern Pacific and the intensity and persistence of low-level westerly zonal wind anomalies. The Climate Prediction Center will continue to monitor these features over the next few months.

Expected global impacts of the warm episode include: 1) drier-than-average over most of Indonesia, Micronesia and northern/northeastern Australia continuing during the next three months, 2) drier-than-average over southeastern Africa during January-March 2003, 3) drier-than-average over Northeast Brazil and northern South America during January-April 2003, and 4) wetter-than-average conditions over coastal sections of Ecuador and northern Peru during February-April 2003. Over the United States and Canada, during the remainder of the northern winter, expected conditions include: 1) drier-than-average over the Ohio and Tennessee Valleys, the eastern Great Lakes, and the northern U.S. Rockies, 2) wetter-than-average along much of the southern tier of the U.S., and 3) warmer-than-average in the northern tier states, southern and southeastern Alaska, and western and central Canada.

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: