above-normal (Fig. T17).
Tropical convection [as inferred from anomalous outgoing longwave radiation (OLR)]
during August was suppressed across the western and central equatorial Pacific and
enhanced across eastern Indonesia and the Philippines (Fig. T25).
This pattern has prevailed since mid-1998, and is also consistent with ongoing cold
episode conditions (Fig. T8). Elsewhere, convection was
again enhanced across the African Sahel, with well-above-normal rainfall recorded in the
region for the second consecutive month (Fig. E4).
The pattern of tropical convection over the western and central equatorial Pacific was
again accompanied by anomalous easterly winds at low-levels (850 hPa) over the western
equatorial Pacific (Fig. T20). These stronger-than-normal
easterlies have prevailed since May 1998 (Fig. T7).
Elsewhere, low-level westerly wind anomalies covered the sub-tropical North Atlantic
during the month, consistent with above-normal rainfall across West Africa.
The upper-level atmospheric circulation (200-hPa) in the Tropics remained consistent
with the pattern of tropical rainfall and cold episode conditions, with well-defined
troughs observed over the low-latitudes of the mid-Pacific in both hemispheres and
amplified low-latitude ridges observed across most of the remainder of the two hemispheres
(Figs. T21, T22).
The Southern Oscillation Index (SOI) was 0.1 (Table T1, Fig. T1), and the equatorial SOI was 0.6 (Fig.
T2) during August. Both of these indices have decreased in magnitude over the past
few months, as positive sea level pressure (SLP) anomalies have overspread most of the
tropical Pacific and Indian Ocean basins (Figs. T6, T19).