Further evolution toward basin-wide mature El Niño conditions occurred during October, as sea surface temperature (SST) anomalies increased in all of the Niño regions (Fig. 1). SST anomalies (departures from average) were greater than +1^oC throughout most of the equatorial Pacific between 180^oW and the South American coast, and SST anomalies exceeded +2^oC between 175^oW and 140^oW (Fig. 2). Positive subsurface temperature departures and a deeper-than-average oceanic thermocline prevailed throughout most of the equatorial Pacific (Fig. 3). Atmospheric indicators of El Niño include consistently negative values of the Southern Oscillation Index (SOI) since March 2002, and weaker-than-average low-level easterly winds since May 2002 throughout the equatorial Pacific. In addition, above-average precipitation has been observed over the tropical Pacific, especially in the vicinity of the date line (180^oW) since August 2002, while drier-than-average conditions prevailed over many sections of Indonesia, India, Mexico and Central America (Fig. 4). These oceanic and atmospheric conditions indicate the presence of El Niño.

Most coupled model and statistical model forecasts indicate that El Niño conditions will continue through spring 2003. Based on the recent evolution of conditions in the tropical Pacific, we expect SST anomalies to increase further in the eastern equatorial Pacific (Niño 3 and Niño 1+2 regions), with the establishment of basin-wide mature El Niño conditions during December 2002-February 2003. However, based on the latest predictions and an assessment of current oceanic and atmospheric conditions, we expect that this event will be weaker than the 1997-98 El Niño.

Expected global impacts include: 1) drier-than-average over Indonesia and eastern Australia continuing during the next several months, 2) wetter-than-average over southeastern South America (Uruguay, northeastern Argentina, and southern Brazil) through the end of 2002, 3) drier-than-average over southeastern Africa during December 2002-February 2003, 4) drier-than-average over Northeast Brazil and northern South America during December 2002-April 2003, and 5) wetter-than-average conditions over coastal sections of Ecuador and northern Peru during December 2002-April 2003. Over the United States and Canada we expect: 1) drier-than-average conditions in the Ohio Valley states and northern U.S. Rockies during winter 2002-2003, 2) wetter-than-average conditions along much of the southern tier of the U.S. during winter 2002-2003, and 3) warmer-than-average conditions in the northern tier states, southern and southeastern Alaska, and western and central Canada during late fall 2002 and winter 2002-2003.

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