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HOME > Expert Assessments > ENSO Diagnostic Discussion
issued by
June 12, 2003

Oceanic and atmospheric conditions in the tropical Pacific during May were consistent with a developing cold episode. Negative sea-surface temperature anomalies strengthened across the central and eastern equatorial Pacific during May, as significant decreases in SST anomalies occurred in all of the Niņo regions (Fig. 1). By early June 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. 2).

Consistent with the trend in SST anomalies, the equatorial easterlies have been near or slightly stronger than average over the central and west-central equatorial Pacific, and the equatorial SOI has been slightly positive during the last two months. 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. 3). By mid-May subsurface temperatures at thermocline depth were below average throughout the eastern Pacific, with negative anomalies ranging between -1°C and -4°C (Fig. 3, 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.

Most statistical and coupled model forecasts indicate that either near-neutral or La Niņa conditions will occur during the last half of 2003. However, current conditions and recent trends favor the development of cold episode (La Niņa) conditions 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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