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Tropical Highlights - June 2001

Near-normal conditions prevailed across the tropical Pacific during June 2001. Sea surface temperatures (SSTs) across the tropical Pacific were again near normal during the month (Fig. T18), with the Niņo 3, Niņo 3.4, and Niņo 4 region indices all within 0.2°C of 0°C (Table T2). The Niņo 3.4 and Niņo 4 values were positive for the first time since the end of the 1997/98 warm episode (Fig. T5).

The equatorial oceanic thermocline remained deeper than normal in the western Pacific, deepened in the central Pacific, and remained shallower than normal in the extreme eastern Pacific during the month (Fig. T15). Consistent with this pattern, oceanic temperatures at thermocline depth were above normal throughout the western and central Pacific and below normal in the extreme eastern Pacific (Fig. T17). Over the past few months, the region of above normal ocean temperatures has shifted east, with positive anomalies at thermocline depth observed across the equatorial Pacific west of 120°W (Fig. T17).

Tropical convection during June was near normal over the west-central and central Pacific and slightly enhanced over the western Pacific and Indonesia (Fig. T25). Over the past few months, the pattern of tropical convection over the western and central Pacific, which has persisted since mid-1998 has weakened (Fig. T11). Elsewhere, convection was enhanced over India and the southern part of the Sahel, implying a good start to the rainy seasons in these two regions.

The low-level (850 hPa) winds across the Pacific basin featured near-normal easterlies across the entire equatorial Pacific (Fig. T20). Enhanced equatorial easterlies had persisted across the western Pacific since the onset of cold episode conditions in mid-1998 (Fig. T7). The West Pacific 850-mb wind index value of 0.1 is the smallest value observed since March 1998 (Fig. T4). At upper levels, near normal winds were observed over the equatorial Pacific, while easterly anomalies were observed throughout the global subtropics of both hemispheres (Fig. T21). These easterly anomalies were associated with enhanced subtropical ridges (Fig. T22), which are typically observed during the mature phase of a cold episode.

The sea level pressure (SLP) pattern during June featured negative SLP anomalies throughout much of the western and central tropical Pacific and small positive anomalies over the extreme eastern Pacific and South America (Fig. T19). This pattern was associated with small values of both the Southern Oscillation Index (SOI) (-0.1) and the equatorial SOI (0.7) (Table T1, Fig. T2).

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