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Forecast Forum
FEBRUARY 2009
Forecast Forum
The
CPC and the contributors to the Forecast Forum caution potential users of
this predictive information that they can expect only modest skill.
ENSO
Alert System Status: La Niña Advisory
Outlook:
La
Niña is expected to gradually weaken with increasing chances (greater than 50%)
for
ENSO
-neutral conditions during the Northern Hemisphere Spring.
Discussion:
Atmospheric
and oceanic conditions during February 2009 continued to reflect La Niña.
Equatorial sea surface temperatures
(SST) across the central and east-central
Pacific Ocean
remained below-average ((Fig. T18),
but weakened throughout the month. The
Niño-3.4 SST index also gradually increased, but remained cooler than
−0.5°C (Table T2).
Negative subsurface oceanic heat content anomalies (average temperatures
in the upper 300m of the ocean) and temperature anomalies at thermocline depth
also weakened across the eastern half of the Pacific (Fig. T17).
However, convection remained suppressed near the Date Line, and enhanced
across
Indonesia
(Fig. T25).
Also, low-level easterly winds and upper-level westerly winds continued
across the equatorial
Pacific Ocean
(Figs. T20
and T21).
Collectively, these oceanic and atmospheric anomalies are consistent with
a weakening La Niña.
While
nearly all the model forecasts for the Niño-3.4 region show that La Niña will
have dissipated by May – July 2009, the exact timing of the transition to
ENSO
-neutral conditions is uncertain (Figs. F1-F13).
The timing of the expected transition will depend on the strength of the
low-level easterly wind anomalies and on how quickly the reservoir of
below-average subsurface temperatures dwindles. Therefore, based on current
observations, recent trends, and model forecasts, La Niña is expected to
gradually weaken with increasing chances (greater than 50%) for
ENSO
-neutral conditions during the Northern
Hemisphere Spring.
Weekly
updates of oceanic and atmospheric conditions are available on the Climate
Prediction
Center
homepage (El
Niño/La Niña Current Conditions and Expert Discussions).
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www.nws.noaa.gov
