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HOME > Expert Assessments > ENSO Diagnostic Discussion
issued by
December 11, 2003

Surface and subsurface temperatures remained warmer than average across most of the equatorial Pacific Ocean during November (Fig. 1 and Fig. 2, respectively). Equatorial ocean surface temperatures greater than +0.5°C (~1°F) above average were found in most areas between Indonesia and the South American coast. Departures greater than +1°C were found between 150°E and 170°W. Positive SST anomalies were observed in all four Niņo index regions for the second consecutive month (Fig. 3). However, the 850-hPa zonal wind indices, OLR index, 200-hPa zonal wind index, SOI and EQSOI all indicate ENSO-neutral conditions. Over the past few months these atmospheric indices have not shown any significant trends that would support either additional large-scale increases or any substantial decreases of SST anomalies in the equatorial Pacific.

A majority of the statistical and coupled model forecasts indicate near-average conditions in the tropical Pacific (Niņo 3.4 SST anomalies between -0.5°C and +0.5°C) through Northern Hemisphere winter 2003-2004. However, some forecasts indicate that weak warm episode conditions will develop during the winter, which is consistent with observed trends in SST anomalies, particularly in the vicinity of the date line.

The three-month (September-November) average SST anomaly in the Niņo 3.4 region (+0.4°C) is just below the threshold (+0.5°C) required for NOAA to declare a weak Pacific warm episode (El Niņo). It is likely that the October-December 2003 average will reach that threshold and that borderline weak El Niņo / ENSO-neutral conditions will persist through the Northern Hemisphere winter of 2003-04. However, it seems unlikely that classical El Niņo conditions will develop along the west coast of South America.

In the past, weak Pacific warm episodes have not shown consistent temperature and precipitation impacts, especially for areas outside the tropical Pacific. Therefore, these conditions are not likely to have significant impacts on the wintertime temperature and precipitation patterns over the United States.

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 temperature 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 CPC's Climate Diagnostics Bulletin Forecast Forum. 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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