Tropical Highlights - August 2003

Current atmospheric and oceanic conditions continue to reflect neutral conditions across the Tropical Pacific and do not support the development of La Niña or El Niño during the next few months. Sea surface temperatures (SSTs) remained slightly warmer than average across the western and west-central Pacific and were slightly cooler than average along the South American coast (Fig. T18). SST anomalies in the four Niño regions exhibited little changes during August (Table T2, Fig. T4).

Oceanic thermocline depths, as measured by the depth of the 20°C isotherm (Figs. T15, T16) was deeper than average across most of the equatorial Pacific during August. This pattern has been modulated by a strong eastward-propagating Kelvin wave that originated in late May/early June. Consistent with the conditions observed during August, oceanic temperatures at thermocline depth were 2-3°C above average in the east-central Pacific and 1-2°C in the western Pacific (Fig. T17).

Both the low-level and upper-level equatorial winds were near average across the Pacific during August (Table T1, Fig. T20), and the Tahiti-Darwin SOI also remained near zero (-0.3) during the month (Table T1, Fig. T1). None of these indicators have exhibited any trend towards warm or cold episodes during the past four months and all are consistent with near neutral conditions across the Tropical Pacific.

Relatively weak outgoing longwave radiation (OLR) anomalies were again observed throughout much of the global Tropics during August (Fig. T25). Enhanced convection (negative OLR anomalies and above-average precipitation) was observed over the west African Sahel (Figs. E3, E4), while suppressed convection (positive OLR anomalies and below-average precipitation) was found over the central Pacific Ocean near the date line (Fig. T25).