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HOME > Expert Assessments > ENSO Diagnostic Discussion
issued by
August 8, 2002

Warm episode (El Niņo) conditions prevailed during July, as SST anomalies (departures from average) remained greater than +1°C throughout the central equatorial Pacific between 170°E and 120°W (Fig. 1). 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 during May-July 2002 throughout the equatorial Pacific.

The Madden-Julian Oscillation (MJO) continues to be 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 a substantial weakening of the low-level easterly winds throughout the equatorial Pacific during July. As a consequence, drier-than-average conditions were observed over Indonesia and portions of Southeast Asia/ India during the month (Fig. 2). In addition, the weaker-than-average easterly winds contributed to a deepening of the oceanic thermocline in the central equatorial Pacific, evident by the increase in subsurface temperature anomalies (Fig. 3), and an increase in SST anomalies in the central equatorial Pacific (Fig. 4) during July.

The oceanic and atmospheric variables discussed above reflect the presence of weak-to-moderate El Niņo conditions. 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 considerable 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 much weaker than the 1997-98 El Niņo. It is important to add that the global impacts of this warm episode should be correspondingly weaker than those observed during the very strong 1997-98 El Niņo.

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.

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: August 8, 2002
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