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HOME > Expert Assessments > ENSO Diagnostic Discussion
issued by
May 19, 2003

Warm episode (El Niņo) conditions rapidly dissipated in the tropical Pacific during March and April 2003, as sea-surface temperature anomalies continued to decrease across the central and eastern equatorial Pacific and drier-than-average conditions developed over the central equatorial Pacific (Fig. 1). Significant deceases in SST anomalies occurred in all of the Niņo regions during April and early May (Fig. 2 and Fig. 3). By mid-May equatorial SSTs were near or below normal between 165°W and the South American coast, with only a small area of residual positive SST anomalies west of the date line between 155°E and 175°E (Fig. 3, bottom panel).

Consistent with the cooling trend in SSTs, the equatorial easterlies have been stronger than average over the central and west-central equatorial Pacific since late February, and the equatorial SOI has switched from negative to positive (Fig. 4). In addition, in recent months the depth of the oceanic thermocline has steadily decreased across the central and eastern equatorial Pacific, and negative subsurface temperature departures have developed and intensified in the upper ocean of this region (Fig. 5). By late-April subsurface temperatures at thermocline depth were below average throughout the eastern Pacific, with negative anomalies ranging between -1°C and -3°C (Fig. 5, bottom panel). These observed trends in oceanic and atmospheric variables indicate that a transition to La Niņa is underway and that La Nina conditions are likely to develop over the next few months.

The latest statistical and coupled model forecasts show a large spread in the forecasts for the next several months. While some indicate the possibility that La Niņa will develop during the second half of 2003, others indicate a resurgence of El Niņo conditions by the end of the year. However, based on current conditions and recent observed trends, it appears likely that cold episode (La Niņa) conditions will develop in the tropical Pacific during the next few months.

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 (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 the monthly ENSO Diagnostic Discussions are released, please send your e-mail address to:

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