CPC and the contributors to the Forecast Forum caution potential users of
this predictive information that they can expect only modest skill.
Alert System Status: Final La Niņa Advisory
are expected to continue into the Northern Hemispheric Summer.
April 2009, the equatorial
transitioned from La
-neutral conditions, ending the 2008-09 La Niņa.
Negative sea surface temperature (SST) anomalies weakened across the
anomalies developed in areas of the eastern Pacific (Fig. T18)
. Correspondingly, the monthly SST
indices were near zero in all Niņo regions, except for the easternmost Niņo-1+2
region (Table T2).
Subsurface oceanic heat content anomalies (average temperatures in the
upper 300m of the ocean) became positive for the first time since mid-August
2008, reflecting an eastward spread of above-average temperatures near
thermocline depth (Fig. T17).
anomalies consistent with La Niņa weakened during April, with enhanced
convection decreasing over
, although convection
remained suppressed near the International Date Line (Fig. T25).
Also, Madden Julian Oscillation (MJO) activity strongly influenced the
atmospheric circulation across the global tropics, and contributed to the
periodic fluctuation in the strength of the low-level easterly winds and
upper-level westerly winds over the equatorial
). Collectively, these oceanic and
atmospheric anomalies are consistent with a transition to ENSO-neutral
A majority of
model forecasts for the Niņo-3.4 region show that ENSO-neutral conditions will
continue through the remainder of 2009 (Figs. F1-F13). The
dynamical models, such as the NCEP Climate Forecast System (CFS), increasingly
favor above-average temperatures in the Niņo-3.4 region, while statistical
models predict below- or near-average temperatures.
Compared to the statistical models, the dynamical models are more
responsive to subsurface temperatures, which have recently increased as positive
anomalies have spread eastward. Based
on current observations, recent trends, and model forecasts, ENSO-neutral
conditions are expected to continue into the Northern Hemisphere Summer.
updates of oceanic and atmospheric conditions are available on the Climate
Niņo/La Niņa Current Conditions and Expert Discussions).