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HOME > Expert Assessments > ENSO Diagnostic Discussion
issued by
September 12, 2002

Warm episode (El Niņo) conditions prevailed during August, as SST anomalies (departures from average) remained greater than +1°C throughout the central equatorial Pacific between 175°E and 130°W (Fig. 1), and positive subsurface temperature departures and a deeper-than-average oceanic thermocline prevailed throughout most of the equatorial Pacific (Fig. 2). Atmospheric indicators of a warm episode (El Niņo) 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, during August above-average precipitation was observed over the tropical Pacific, especially in the vicinity of the date line (180°W), while drier-than-average conditions prevailed over many sections of Indonesia, Mexico and Central America (Fig. 3). These oceanic and atmospheric conditions reflect the presence of El Niņo conditions.

The Madden-Julian Oscillation (MJO) has been a major source of week-to-week and month-to-month variability in the atmospheric circulation of the Tropics and subtropics. The MJO contributed to substantial weakening of the low-level easterly winds throughout the equatorial Pacific during late May and again in early July. During August the MJO weakened, as a more persistent pattern of weaker-than average easterly winds and enhanced cloudiness and precipitation developed over the central equatorial Pacific Most coupled model and statistical model forecasts indicate that El Niņo conditions are likely to continue through the end of 2002 and into early 2003. Although there is some uncertainty in the forecasts about the timing and intensity of the peak of this warm episode, all of the forecasts indicate that it will be weaker than the 1997-98 El Niņo. It is important to add that the global impacts of this warm episode should generally be weaker than those observed during the very strong 1997-98 El Niņo. However, strong impacts are still possible in a few locations.

Based on the current conditions in the tropical Pacific, on the SST predictions, and on results from historical studies of the effects of ENSO, we expect drier-than-average conditions to continue over Indonesia and eastern Australia during the next several months, and wetter-than-average conditions over southeastern South America during the next three months. Over North America drier-than-average conditions are expected in the Pacific Northwest and mid-Atlantic states during fall 2002 and in the Ohio Valley states during winter 2002-2003. Wetter-than-average conditions are expected in the Gulf Coast states during winter 2002-2003, and warmer-than-average conditions are expected in the northern tier of the conterminous United States, southern/southeastern Alaska, and western and central Canada during late fall 2002 and winter 2002-2003.

This discussion is a team effort of NOAA and its funded institutions. Updates of SST, 850-hPa wind, OLR and the equatorial subsurface temperature structure are available on the Climate Prediction Center web page at (Weekly Update).  Forecasts for the evolution of El Niņo/La Niņa 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:

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Page Author: Climate Prediction Center Internet Team
Page last modified: September 12, 2002
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