Tropical Highlights - April 2005

     

The pattern of global tropical sea surface temperature (SST) during April 2005 featured negative anomalies in the eastern equatorial Pacific and near-average SSTs elsewhere. The SST anomaly in the Niño 3.4 region remained 0.4 during April and the Niño 1+2 anomaly remained negative, with an April value of -0.6 (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 -1.0, Table T1, Fig. T1) was 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 slightly shallower than average in the eastern equatorial Pacific during April (Figs. T15, T16). Consistent with these conditions, oceanic temperatures at thermocline depth were 2-4°C above average across the central and east-central equatorial Pacific and near 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 April 2005, except for over the western (west-central) equatorial Pacific, where strong low-level westerly (easterly) anomalies (more than 3.0 m s^-1) were observed (Fig. T20). This pattern is consistent with enhanced convection over the western and west-central tropical Pacific (between 140^oE and the dateline) (Fig. T25).