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Tropical Highlights
NOVEMBER 2007
Forecast Forum
During
November 2007, equatorial sea surface temperature (SST) anomalies became
increasingly negative from 160ºE to the South American coast (Fig.
T18). This cooling is reflected by a
drop in the monthly Niño-3.4 index to -1.5°C and a drop in the Niño-4 index
to -0.9°C (Table
T2). The sub-surface temperature departures
remained negative across the eastern equatorial Pacific,
where temperatures at thermocline depth ranged from -2°C to -4°C below
average (Fig.
T17).
During
November 2007, low-level easterly anomalies (more than
3.0 m s-1) and upper-level westerly anomalies (more than 5.0 m s-1)
spanned the central equatorial Pacific (Figs.
T20, T21). This
pattern is consistent with a shallower-than-average thermocline and the
additional cooling of the surface and sub-surface ocean temperatures (Figs. T15, T16).
These conditions were associated with enhanced convection (above-average
rainfall amounts) over the western equatorial Pacific and a continuation
of suppressed convection (below-average rainfall amounts) across the central
and eastern equatorial Pacific (Figs. T25,
T26, E3).
Consistent with these anomalies, the
Tahiti
– Darwin SOI increased to +0.9 during November (Table
T1, Fig. T1). Collectively, these oceanic and
atmospheric conditions reflect a strengthening La Niña.
For the latest status of the ENSO cycle see the ENSO Diagnostic Discussion at:
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
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