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

Sea surface temperature (SST) anomalies decreased in the equatorial Pacific everywhere east of the date line during January 2005, resulting in decreases in all of the Niño indices with the exception of Niño 4 (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 early February 2005, positive equatorial SST anomalies greater than +0.5°C (~0.9°F) were found from 140°E eastward to 155°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, through December there was a lack of persistent enhanced convection over the anomalously warm waters of the central equatorial Pacific, which limited El Niño-related impacts.

Since late 2003 MJO activity has resulted in week-to-week and month-to-month variability in many atmospheric and oceanic indices. The MJO activity weakened considerably during early November 2004 and remained weak through mid-December. During the last half of December the MJO strengthened, as enhanced convection and precipitation over the Indian Ocean shifted eastward across Indonesia into the western tropical Pacific. Since early January enhanced convection has persisted in the western equatorial Pacific and expanded eastward into the central equatorial Pacific (Fig. 4), accompanied by a weakening of the low-level easterly winds over the region. At this time it is not clear whether the recent enhanced convection and weakening of the easterly winds in the central equatorial Pacific are transient features (related to the MJO) or perhaps evidence of a coupling between the anomalously warm waters and the overlying atmospheric circulation.

Based on the recent evolution of oceanic and atmospheric conditions and on a majority of the statistical and coupled model forecasts, it seems most likely that weak warm episode (El Niño) conditions will gradually weaken during the next three months and that ENSO-neutral conditions will prevail during the last half of 2005

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 3 March 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.