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HOME > Expert Assessments > ENSO Diagnostic Discussion
issued by
July 8, 2004

Synopsis: ENSO-neutral conditions are expected to continue during the next 3 months.

Oceanic and atmospheric conditions in the Pacific basin continued to reflect the neutral phase of the ENSO cycle during June 2004. Sea surface temperatures were warmer-than-average in the western equatorial Pacific (Niņo 4 region), near average in the central equatorial Pacific (Niņo 3.4 and Niņo 3 regions) and cooler-than-average in the eastern equatorial Pacific (Niņo 1+2 region) during the month (Fig. 1). Positive SST anomalies greater than +0.5°C (~1°F) were found between 160°E and 150°W, while negative SST anomalies less than -0.5°C were found between 95°W and the South American coast (Fig. 2).

During the past several months, positive SST anomalies have persisted in the west-central equatorial Pacific (150°E-160°W), low-level easterly wind anomalies (enhanced east-to-west flow) have been observed over the central equatorial Pacific, and low-level westerly anomalies have persisted over the western equatorial Pacific (Fig. 3, top). These features have favored persistent enhanced tropical convection (negative OLR anomalies) in the region 140°E-180°W (Fig. 3, bottom). The low-level easterly wind anomalies over the central equatorial Pacific have also contributed to a steeper-than-average thermocline slope in the upper ocean, which is reflected in the pattern of subsurface temperature anomalies [positive (negative) in the central-western (eastern) equatorial Pacific] (Fig. 4). Both the surface and subsurface temperature fields showed trends toward near-average conditions (decreased magnitude of the anomalies) during June.

Considerable intraseasonal variability (MJO activity) in recent months has resulted in week-to-week and month-to-month variability in many atmospheric and oceanic indices. 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. The greatest wind and convection anomalies occurred north of the equator in the western Pacific, associated with two typhoons. It is too early to determine whether this event will have any significant impact on the thermal structure of the equatorial Pacific Ocean.

Slightly more than half of the statistical and coupled model forecasts indicate near neutral conditions in the tropical Pacific (Niņo 3.4 SST anomalies between -0.5°C and +0.5°C) through the northern summer and fall 2004. The remaining forecasts indicate borderline El Niņo conditions (Niņo 3.4 SST anomalies slightly greater than +0.5°C) will develop within the next 3-6 months. Given the recent trends and observed oceanic and atmospheric patterns discussed above, ENSO-neutral conditions are expected to continue for the next 3 months (through September 2004).

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. 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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Page last modified: July 10, 2003
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