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HOME > Expert Assessments > ENSO Diagnostic Discussion
issued by
January 6, 2005
Spanish Version (Español -- Courtesy of INFOCLIMA, Peru)

Synopsis: Weak warm-episode (El Niņo) conditions are expected to continue for the next three months.

Positive sea surface temperature (SST) anomalies greater than +0.5°C (~1°F) persisted across most of the central and western equatorial Pacific during December 2004 (Fig. 1). By the end of the month, positive equatorial SST anomalies greater than +1°C (~2°F) were found from 160°E eastward to 155°W and locally in the region near 110°W (Fig. 2). During December SST anomalies exceeded 0.5°C in the Niņo 4, Niņo 3.4 and Niņo 3 regions, while anomalies remained near zero along the West Coast of South America (Niņo 1+2 region) (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 (-0.6) indicate that a weak warm (mid-Pacific El Niņo) episode has developed. However, through December there has been a lack of persistent enhanced convection over the anomalously warm waters of the central equatorial Pacific (Fig. 4), which has limited El Niņo-related impacts on the global pattern of precipitation. (Note: The recent pattern of heavy precipitation in California has been associated with 1) a persistent high-latitude blocking ridge in the vicinity of the Gulf of Alaska and an associated trough along the West Coast, and 2) a weaker than average jetstream across the central and eastern Pacific. These circulation features are not consistent with El Niņo, which would favor a stronger-than-average jetstream over the central and eastern Pacific and a reduced tendency for blocking in the Gulf of Alaska.

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. However, during the last half of December the MJO strengthened, as enhanced convection and precipitation over the Indian Ocean shifted eastward across Indonesia (Fig. 5). By early January 2005, enhanced convection extended into the western tropical Pacific. The Climate Prediction Center will continue to closely monitor the evolution of this activity over the next several weeks as it shifts eastward over the abnormally warm waters in the central equatorial Pacific.

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 Niņo) conditions will persist for at least the next three months. However, there is considerable uncertainty concerning future developments in the extreme eastern equatorial Pacific (the classical El Niņo region).

Expected global impacts include drier-than-average conditions over portions of Indonesia (through early 2005), northern and northeastern Australia (through February 2005), and southeastern Africa (through March 2005). If the warming in the tropical Pacific strengthens and spreads eastward to the South American coast, then wetter-than-average conditions would be expected in coastal sections of Ecuador and northern Peru during March-April 2005, and drier-than-average conditions would be expected to develop in Northeast Brazil during February through April 2005. Expected US impacts during Northern Hemisphere winter include warmer- than-average conditions in the West and in the northern Plains, and cooler- and wetter-than-average conditions for portions of the South and Southeast.

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 (Weekly Update). Forecasts for the evolution of El Niņo/La Niņa are updated monthly in the Forecast Forum section of CPC's Climate Diagnostics Bulletin. The next ENSO Diagnostics Discussion is scheduled for 10 February 2005.  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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