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Tropical Highlights - October 2000

Sea surface temperatures (SSTs) remained weakly negative over portions of the central and eastern equatorial Pacific during October, with all four Niņo region indices indicating SSTs within 0.5°C of normal for the third consecutive month (Fig. T18, Table T2). The oceanic thermocline was deeper than normal west of 130°W during the month (Fig. T16), as the thermocline deepened in the central Pacific during October (Fig. T15). Consistent with this pattern, temperature anomalies at thermocline depth were weakly positive across the central Pacific and weakly negative in the eastern Pacific (Fig. T17).

Tropical convection during October [as inferred from anomalous outgoing longwave radiation (OLR)] was slightly below-normal over the western and central Pacific (Figs. T1, T25) and above normal over Indonesia. The large increase in convection over Indonesia was associated with tropical intraseasonal activity (Madden-Julian Oscillation-MJO), which has persisted during the past 6 months with a period near 45 days (Fig. T11).

Low-level (850 hPa) easterly wind anomalies persisted over the western equatorial Pacific during October (Fig. T20, Table T1), while anomalous cross-equatorial flow continued over the central tropical Pacific. This pattern of low-level winds was consistent with the suppressed convection over the central tropical Pacific, and also with a strengthening of the ITCZ over the eastern Pacific (Fig. T25). At upper levels, westerly anomalies were observed over the central equatorial Pacific, in association with an anomalous cyclonic couplet centered near the date line (Fig. T21).

The sea level pressure (SLP) pattern across the Tropics during October featured negative anomalies extending from the eastern Indian Ocean across Indonesia to the western Pacific (Fig. T19). These anomalies were associated with positive values of both the Southern Oscillation Index (SOI) (1.0) and the equatorial SOI (1.3) during the month (Table T1, Fig. T2).

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