Tropical Highlights - November 2002
The evolution toward mature Pacific warm episode (El Niño)
conditions continued during November 2002 as sea surface temperatures
(SST) and SST anomalies increased across the equatorial Pacific east
of the date line (Table T2). Positive SST anomalies exceeded +2°C
across much of the equatorial Pacific between the date line and 110°W,
and exceeded +1°C between 170°E
and the west coast of South America (Fig. T18). Consistent with
this warmth the Niño 3.4
SST index increased to 1.8, its largest value since February 1998 near
the end of the 1997-98 El Niño
episode (Fig. T5, Table T2).
Consistent with this evolution the oceanic thermocline has steadily
deepened across the eastern half of the equatorial Pacific during the
past few months, and was more than 30 m deeper than average between
160°W and 100°W
during November, and more than 50 m deeper than average between 135°W
and 120°W (Figs. T15, T16).
In the western Pacific the thermocline has shoaled in recent months,
and was 10 m shallower than normal during November. At thermocline
depth sub-surface ocean temperatures have increased to 6-7°C
above normal between 155°W
and 130°W, and decreased to
1-2°C below normal in the
western equatorial Pacific (Fig. T17). This pattern of
sub-surface ocean temperatures is consistent with developing mature
warm episode conditions.
Convection remained enhanced across the central equatorial Pacific
and suppressed over Indonesia and the western Pacific during November
(Fig. T25). This pattern has persisted since August (Fig.
T11) and is also consistent with ongoing warm episode conditions.
Because of the enhanced convection near the date line the central
Pacific OLR index has averaged -1.5 since August (Table T1),
its lowest value since late 1997 (Fig T1).
The upper-level circulation featured anticyclonic circulation
anomalies in the subtropics of both hemispheres over the central
Pacific (Fig. T22). These anomalies flanked the region of
enhanced convection over the central equatorial Pacific, and are
consistent with the atmospheric response to mature El Niño
The tropical sea-level pressure (SLP) pattern reflected an
anomalous wave-1 pattern during November, with below-average pressure
over most of the tropical Pacific and above-average pressure elsewhere
(Fig. T19). This pattern again resulted in small, negative
values of both the Tahiti-Darwin Southern Oscillation Index (SOI)
(-0.6) and the equatorial SOI (-0.4) (Figs. T1,
The SOI has fluctuated between -0.5 and -1.5 since March 2002 (Table
T1), with the most recent five-month running mean of -0.9.