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HOME > Expert Assessments > ENSO Diagnostic Discussion
issued by
January 9, 2002

The evolution towards a warm episode in the tropical Pacific continued during December 2001, as enhanced convection developed over the equatorial central Pacific for the first time since the 1997-98 El Niņo episode. In addition, the Tahiti-Darwin SOI (-1.2) and the equatorial SOI (-0.8) were the lowest since early 1998. By early January 2002 equatorial SST anomalies increased to +1°C at the date line (Fig. 1).

In recent months, many tropical Pacific atmospheric and oceanic variables have been strongly modulated by intraseasonal (30-60 day) fluctuations, associated with the Madden-Julian Oscillation (MJO). Low-level wind fluctuations over the central and western tropical Pacific have been consistent with this activity. Significant low-level westerly wind anomalies occurred over the western equatorial Pacific during mid-October. November featured a return to easterly anomalies in this region during the first three weeks, followed by westerly anomalies during late November. December featured significant low-level westerly anomalies over the western equatorial Pacific during the first half of the month and over the west-central equatorial Pacific during the second half of the month, as the period of the MJO appeared to lengthen. This activity generated a strong eastward propagating oceanic Kelvin wave that contributed to the deepening of the oceanic thermocline and an increase in subsurface temperature anomalies in the vicinity of the date line (Fig. 2). The magnitude of this Kelvin wave suggests that an increase in SST anomalies, with negative anomalies possibly being replaced by positive anomalies, is likely to occur in the eastern Pacific in late January or early February.

The latest statistical and coupled model predictions show a spread ranging from near-normal to moderate warm episode conditions over the next 3-6 months. All of these prediction techniques have difficulty in making skillful forecasts during ENSO transition periods. Considering the observed oceanic and atmospheric circulation patterns and their recent evolution, it seems most likely that warm-episode conditions will develop in the tropical Pacific during the next 3-6 months.

Weekly updates for SST, 850-hPa wind, OLR and the equatorial subsurface temperature structure are available on the Climate Prediction Center homepage 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 last modified: January 9, 2002
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