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Tropical Highlights - December 2003

Surface and sub-surface oceanic conditions across the Tropical Pacific remained slightly warmer than average during December 2003 (Table T2), while atmospheric features continued to reflect ENSO-neutral conditions (Table T1). Although sea surface temperature (SST) anomalies remained above average across the entire equatorial Pacific, the departures across the central Pacific decreased from November (Fig. T5). The largest SST departures (exceeding 1C) remained in the western Pacific between 160E and the date line (Fig. T18).

Oceanic thermocline depths, measured by the depth of the 20C isotherm (Figs. T15, T16), remained slightly deeper than average across most of the equatorial Pacific during December. Thermocline depths have been slightly deeper than normal across most of the equatorial Pacific since May (Fig. T15). Consistent with these conditions, oceanic temperatures at thermocline depth remained 1-2̊C above average across most of the equatorial Pacific (Fig. T17).

The low-level (850-hPa) equatorial winds were stronger than average across the central and western Pacific and near average over the eastern Pacific during December 2003 (Fig. T20, Table T1). The index values in the western and central Pacific regions are the largest since April and February 2001, respectively (Fig. T4). The Tahiti-Darwin SOI was 1.1 during the month, the largest value of this index since February 2001. These indices have, however, exhibited large week-to-week variability since late November, in response to stronger intraseasonal (Madden-Julian Oscillation) activity (Figs. T12, T13).

Tropical outgoing longwave radiation (OLR) anomalies were negative (enhanced cloudiness and precipitation) over Indonesia, northern Australia, and near 10N across the central Pacific and positive along and just south of the equator near the date line (Fig. T25). Tropical convection was also influenced by intraseasonal activity during the month, although there continues to be a tendency for enhanced equatorial convection to persist over the Pacific between 130E and 160E (Fig. T11).


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