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: La
or La Niña conditions are equally likely during May-June 2011.
Niña persisted during January 2011 as reflected by well below-average sea
surface temperatures (SSTs) across much of the equatorial Pacific Ocean (Fig.
However, some weakening was evident in certain atmospheric and oceanic
anomalies, in part due to Madden-Julian Oscillation activity.
Most Niño indices were between –1.4°C and –1.7°C for the month,
with the easternmost Niño-1+2 region warming to –0.7°C (Table T2). A
lessening of the negative subsurface oceanic heat content anomalies (average
temperatures in the upper 300m of the ocean) was observed mostly in association
with an eastward shift in the above-average temperatures at depth in the central
equatorial Pacific (Fig. T17). Convection remained
enhanced over Indonesia and suppressed over the western and central equatorial
Pacific (Fig. T25).
Also over the western and central equatorial Pacific, the anomalous
low-level easterly and upper-level westerly winds decreased in magnitude (Figs.
T20, T21). Collectively,
these oceanic and atmospheric anomalies reflect an ongoing, mature La Niña that
has begun to weaken.
all of the ENSO model forecasts weaken La Niña in the coming months (Figs.
A majority of the models predict a return to ENSO-neutral conditions by
May-June-July 2011, although some models persist a weaker La Niña into the
Northern Hemisphere summer 2011. Recent
trends in the observations and models do not offer many hints on which outcome
is more likely. Also, model skill is
historically at a minimum during the Northern Hemisphere spring (the “spring
barrier”). Therefore La Niña is
expected to weaken during the next several months, with ENSO-neutral or La Niña
conditions equally likely during May-June 2011.
updates of oceanic and atmospheric conditions are available on the Climate
Niño/La Niña Current Conditions and Expert Discussions).