Forecast Forum
MAY 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 Watch
Outlook:
Conditions
are favorable for a transition from ENSO-neutral to El Niņo conditions during
June − August 2009.
Discussion:
ENSO
-neutral conditions
persisted across the equatorial
Pacific Ocean
during May 2009.
However, sea surface temperatures (SST) departures increased for the fifth
consecutive month, with above-average temperatures extending across the
equatorial
Pacific Ocean
by the end of May (Fig.
T18).
Accordingly, the monthly SST indices ranged between +0.3° to +0.6°C in
all four Niņo regions (Table T2).
Subsurface oceanic heat content anomalies (average temperatures in the
upper 300m of the ocean) also continued to increase in response to a large area
of above-average temperatures (+1° to +3°C) near thermocline depth (Fig.
T17). These
surface and subsurface oceanic anomalies typically precede the development of El
Niņo.
From
early 2007 through April 2009, enhanced low-level easterly winds persisted near
the Date Line, interrupted only briefly by Madden- Julian Oscillation (MJO)
activity (Fig. T20). However, during May 2009,
both the lower-level equatorial winds were near-average in that region despite
the absence of the MJO. Also,
suppressed convection expanded westward along the equator from the Date Line to
Indonesia
(Fig. T25).
The recent oceanic and atmospheric anomalies are consistent with ENSO-neutral
conditions, but also reflect the evolution towards a potential El Niņo.
There
continues to be considerable spread in the model forecasts for the Niņo-3.4
region (Figs. F1-F13). All statistical models
predict
ENSO
-neutral conditions
will continue for the remainder of 2009. However,
most dynamical models, including the NCEP Climate Forecast System, predict the
onset of El Niņo during June − August 2009.
Current observations, recent trends, and the dynamical model forecasts
indicate that conditions are favorable for a transition from
ENSO
-neutral
to El Niņo conditions during June − August 2009.
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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