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
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,
Consistent with these anomalies, the
– 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: