Tropical Highlights - February 2003

Pacific warm episode (El Niño) conditions continued to weaken during February 2003 as sea surface temperature (SST) anomalies decreased across the equatorial Pacific (Table T2). SSTs remained more than 1.0°C above normal in the central Pacific between 170°E and 155°W, but were slightly cooler than normal east of 120°W (Fig. T18). The anomalies in all four Niño region indices decreased for the second consecutive month, with the largest decrease again occurring in the Niño 3 region (Table T2, Fig. T5). The values observed in both Niño 3 and Niño 3.4 were the smallest since May 2002 (Table T2, Fig. T5).

Consistent with weakening El Niño conditions, the oceanic thermocline continued to shoal across the east-central and eastern equatorial Pacific, with near-normal depths observed during February across the central and eastern Pacific (Figs. T15, T16). The shoaling has contributed to a decrease in upper-ocean heat content, with anomalies decreasing to 1-2°C above normal in the central and east-central Pacific (Fig. T17). Also associated with this decrease in thermoclime depth, negative ocean temperature anomalies (1-2°C below normal) were recorded beneath the positive anomalies in the east-central Pacific.

Convection (precipitation and cloudiness) remained enhanced across the central equatorial Pacific and was near-normal or slightly above normal over Indonesia during February (Fig. T25). Enhanced convection has persisted over the central equatorial Pacific since August (Fig. T11), consistent with ongoing warm episode conditions. Elsewhere, the pattern of convection in the south-central Pacific reflected an eastward shift from normal in the position of the South Pacific Convergence Zone.

The tropical sea-level pressure (SLP) pattern during February featured small negative SLP anomalies over the Indian and Pacific oceans and small positive anomalies over the Atlantic (Fig. T19). This pattern was associated with negative values of both the Tahiti-Darwin Southern Oscillation Index (SOI) (-1,2) and the equatorial SOI (-0.2) (Figs. T1, T2, respectively). The SOI has been negative for the past twelve months (Fig. T1).