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Forecast Forum
SEPTEMBER 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: El
Niņo Advisory
Outlook:
El Niņo is expected to
strengthen and last through the Northern Hemisphere
Winter 2009-2010.
Discussion:
A
weak El Niņo continued during September 2009, as sea surface temperature (SST)
anomalies remained nearly unchanged across much of the equatorial
Pacific Ocean
(Fig. T9).
Since the transition to El Niņo conditions during June, the monthly values of
the Niņo-3.4 index have remained between +0.6°C and +0.9°C (Table T2). Subsurface
oceanic heat content (average temperatures in the upper 300m of the ocean)
anomalies continued to reflect a deep layer of anomalous warmth between the
ocean surface and the thermocline, particularly in the central and east-central
Pacific (Fig. T17). The
pattern of tropical convection also remained consistent with El Niņo, with
enhanced convection over the west-central Pacific and suppressed convection over
Indonesia
(Fig. T25).
In addition, two westerly wind bursts were observed over the western
equatorial Pacific, the first occurring early in the month and the second
occurring near the end of the month (Fig. T13).
These oceanic and atmospheric anomalies reflect an ongoing weak El Niņo.
A
majority of the model forecasts for the Niņo-3.4 SST index (Figs.
F1-F13) suggest
that El Niņo will reach at least moderate strength during the Northern
Hemisphere fall (3-month Niņo-3.4 SST index of +1.0°C or greater).
Many model forecasts even suggest a strong El Niņo (3-month Niņo-3.4
SST index in excess of +1.5°C) during the fall and winter, but in recent months
some models, including the NCEP
CFS
, have over-predicted
the degree of warming observed so far in the Niņo-3.4 region.
Based on the model forecasts, the seasonality of El Niņo, and the
continuation of westerly wind bursts, El Niņo is expected to strengthen and
most likely peak at moderate strength.
Weekly
updates of oceanic and atmospheric conditions are available on the Climate
Prediction
Center
homepage (El
Niņo/La Niņa Current Conditions and Expert Discussions).
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www.nws.noaa.gov
