Tropical Highlights - March 2005

     Sea surface temperature (SST) anomalies remained positive across the central equatorial Pacific and negative in the eastern equatorial Pacific during March 2005, with a March value of 0.4 in the Niño 3.4 region and -0.9 in the Niño 1+2 region (Fig. T18, Table T2). Meanwhile, atmospheric features continued to show month-to-month variability associated with intraseasonal (Madden-Julian Oscillation - MJO) activity (Figs. T11, T12, T13, Table T1). The Tahiti - Darwin SOI (latest value -0.2, Table T1, Fig. T1) was slightly negative, primarily in response to higher-than-average pressure over Darwin.

     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 March (Figs. T15, T16). Consistent with these conditions, oceanic temperatures at thermocline depth were 2-6°C above average across the central equatorial Pacific and 2-4°C below normal in the eastern equatorial Pacific (Fig. T17).

     The monthly low-level (850-hPa) and upper-level (200-hPa) equatorial zonal wind indices, the Tahiti-Darwin SOI and the outgoing longwave radiation (OLR) index have all exhibited considerable variability since January 2004 in association with intraseasonal (Madden-Julian Oscillation) activity (Table T1).

     Near-average low-level winds were observed over most of the tropical regions during March 2005, except that strong low-level westerly anomalies (more than 3.0 m s-1) were observed over the eastern equatorial Pacific (Fig. T20). The global Tropics featured enhanced convection over the eastern tropical Pacific (near the west coast of Central America) and near-average convection elsewhere (Fig. T25).