Tropical Highlights - February 2005

Positive sea surface temperature (SST) anomalies persisted in the central equatorial Pacific during February 2005.  SST departures decreased throughout the equatorial Pacific east of the date line, as negative SST anomalies in the eastern equatorial Pacific expanded westward.  Negative SST anomalies were observed in the Niño 1+2 (-0.6) and Niño 3 (-0.2) regions (Fig. T18, Table T2). The SST anomaly in the Niño 3.4 region decreased to 0.3 (Table T2). 

In spite of the recent cooling trend in the SSTs, the Tahiti-Darwin SOI (Table T1, Fig. T1) fell to -4.1 in February, which is the lowest monthly value of the SOI since February 1983. This is consistent with the patterns of strongly enhanced convection (Fig. T25) and low-level westerly anomalies (Fig. T20), that persisted over the central equatorial Pacific throughout the month. It is noteworthy that most of Australia , southern Africa and tropical South America observed rainfall deficits during the month.

The oceanic thermocline, measured by the depth of the 20°C isotherm, remained deeper than average across the central and east-central equatorial Pacific and shallower than average in the eastern equatorial Pacific during February (Figs. T15, T16). Consistent with these conditions, subsurface ocean temperatures at thermocline depth were 2-3°C above average across the central equatorial Pacific and 2-4°C below average in the eastern equatorial Pacific (Fig. T17).