Synopsis: A transition from weak warm-episode (El Niño) conditions to ENSO-neutral conditions is expected to continue during the next three months.

Sea surface temperature(SST) anomalies decreased in all of the Niño regions during February 2005 (Fig. 1). However, positive sea surface temperature (SST) anomalies greater than +1°C (~1.8°F) persisted in portions of the central and western equatorial Pacific (Fig. 2). By late February 2005, positive equatorial SST anomalies greater than +0.5°C (~0.9°F) were found from 155°E eastward to 165°W (Fig. 3). The pattern of anomalous warmth in the equatorial Pacific in recent months and the most recent 5-month running mean value of the Southern Oscillation Index (-0.5) indicate that a weak warm (mid-Pacific El Niño) episode is in progress. However, the recent decrease in SST anomalies throughout the equatorial Pacific suggests that a return to ENSO-neutral conditions is taking place.

In spite of the recent trend in SST anomalies, drier-than-average conditions prevailed over Indonesia and northern Australia during February, while enhanced convection and precipitation persisted over the anomalously warm waters of the central equatorial Pacific (Fig. 4, top panel). This enhanced convection has been accompanied by strong low-level westerly wind anomalies (Fig. 4, bottom panel) that initiated an eastward-propagating oceanic Kelvin wave (Fig. 5). This wave appears to be stronger than those that have occurred in recent months in association with MJO activity. At this time there is uncertainty concerning the possible influence of this latest Kelvin wave on the surface and subsurface conditions in the eastern equatorial Pacific.

Based on the recent evolution of SST anomalies and on a majority of the statistical and coupled model forecasts, it seems most likely that weak warm episode (El Niño) conditions will continue to weaken during the next three months and that ENSO-neutral conditions will prevail during the northern summer. Some lingering effects of the weak warm episode, such as drier-than-average conditions over portions of Indonesia, may continue to be experienced for the next month or two.

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 thermal structure are available on the Climate Prediction Center web page at http://www.cpc.ncep.noaa.gov (Weekly Update). Forecasts for the evolution of El Niño/La Niña are updated monthly in the Forecast Forum section of CPC's Climate Diagnostics Bulletin. The next ENSO Diagnostics Discussion is scheduled for 7 April 2005.  To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send your e-mail address to: ncep.list.enso-update@noaa.gov.