December-February 2004-05: Seasonal Climate Summary

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December-February 2004-05: Seasonal Climate Summary

Dr. Gerald Bell

NOAA/ NWS/ Climate Prediction Center



  1. A weak Pacific warm episode (El Niño) continues

  2. Ongoing intraseasonal variability dominates ENSO signal


Positive sea surface temperature (SST) anomalies greater than +1.0°C (~2°F) were observed in the central equatorial Pacific during December-February (DJF), reflecting a continuation of weak warm (El Niño) episode conditions. However, the spatial coverage of the largest positive anomalies decreased as the season progressed, and by February anomalies greater than 1°C were confined to the date line. Aspects of the tropical rainfall pattern were consistent with past Pacific warm episodes. These included enhanced rainfall over the central equatorial Pacific during February, and suppressed rainfall over Indonesia and northern Australia, the Amazon basin, and southern Africa.

Considerable intra-seasonal variability was also evident in the patterns of tropical convection, which modulated the ENSO signal across the tropical Pacific. This intraseasonal variability contributed to large fluctuations in atmospheric circulation anomalies over the eastern North Pacific and North America, and likely contributed to excess precipitation in California and the southwestern U.S. during January (see Extratropics). During the past six months, the intraseasonal activity has also been associated with periods of weaker-than-average easterlies that have initiated eastward-propagating oceanic Kelvin waves. These Kelvin waves have contributed to fluctuations in sea-surface temperatures over the central and eastern equatorial Pacific, and to fluctuations in the depth of the oceanic thermocline in these regions.

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