Skip Navigation Links 
NOAA logo - Click to go to the NOAA home page National Weather Service   NWS logo - Click to go to the NWS home page
Climate Prediction Center

CPC Search
About Us
   Our Mission
   Who We Are

Contact Us
   CPC Information
   CPC Web Team

HOME > Expert Assessments > ENSO Diagnostic Discussion
issued by
September 9, 2004

Synopsis: Warm-episode conditions are expected to continue into early 2005.

Positive sea surface temperature (SST) anomalies greater than +0.5°C persisted in the central and western equatorial Pacific during August 2004 (Fig. 1). By early September, positive SST anomalies greater than +0.5°C (~1°F) were found between 160°E and 120°W, with anomalies greater than +1°C extending from 170°E eastward to 140°W (Fig. 2).   The increase and eastward expansion of the area of anomalous warmth in the central equatorial Pacific during July-August indicate the early stages of a warm (El Niņo) episode. Through the end of August conditions were not yet indicative of a basin-wide El Niņo, particularly due to the presence of below normal sea-surface temperatures in the far eastern equatorial Pacific from about 120oW eastward to the South American coast (Fig. 2). 

In spite of the anomalous warmth in the central equatorial Pacific during August, there appears to be little or no reflection of that warmth in the average pattern of deep convection (precipitation) over the region (Fig. 3). However, the warmth has contributed to farther eastward shifts in enhanced convection associated with the convectively active phase of the Madden Julian Oscillation (MJO). MJO activity in recent months has resulted in week-to-week and month-to-month variability in many atmospheric and oceanic indices. For example, during mid-June through early July the easterlies weakened in many areas of the equatorial Pacific, as enhanced convection shifted eastward from the Indian Ocean to the western tropical Pacific. By mid-July the low-level winds and equatorial convection returned to near average in many areas of the equatorial Pacific. However, a strong oceanic Kelvin wave, initiated by the weaker-than-average easterly winds in June, propagated eastward resulting in a substantial deepening of the oceanic thermocline and an increase in the subsurface temperature anomalies in the central and eastern equatorial Pacific (Fig. 4). This Kelvin wave reached the South American coast during late August, resulting in an increase in SSTs in along the coasts of Ecuador and northern Peru (Fig. 5). Another substantial weakening of the equatorial easterlies during late August appears to have initiated another eastward-propagating Kelvin wave in the central equatorial Pacific. 

The NOAA operational definition for El Niņo [Oceanic Niņo Index (ONI), a three-month running mean of the Niņo 3.4 index, greater than or equal to +0.5°C] was satisfied for the period June-August 2004, with a value of +0.7°C. 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 SST anomalies in the Niņo 3.4 region will remain positive, at or above +0.5°C, through early 2005. At this time it is not clear what, if any, impacts this event will have on ocean temperatures in the classical El Niņo region (Niņo 1+2) along the west coast of South America. CPC will continue to monitor the situation in the tropical Pacific and will provide more detailed information on possible regional impacts due to this event in coming 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 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 7 October 2004.  To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send your e-mail address to: or to

Climate Prediction Center
National Centers for Environmental Prediction
NOAA/National Weather Service
Camp Springs, MD 20746-4304

NOAA/ National Weather Service
National Centers for Environmental Prediction
Climate Prediction Center
5200 Auth Road
Camp Springs, Maryland 20746
Climate Prediction Center Web Team
Page last modified: July 10, 2003
Disclaimer Privacy Notice