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The canonical correlation analysis (CCA) forecast
of SST in the central Pacific (Barnett et al. 1988, Science, 241, 192-196;
Barnston and Ropelewski 1992, J. Climate, 5, 1316-1345), is shown in Figs.
F1 and F2. This forecast is produced
routinely by the Prediction Branch of the Climate Prediction Center. The predictions from
the National Centers for Environmental Prediction (NCEP) coupled ocean/atmosphere model
(Ji et al. 1998, Mon. Wea. Rev, 126, 1022-1034) are presented in Figs. F3 and F4. Predictions from the latest
version of the LDEO model (Chen, D., M. A. Cane, S. E. Zebiak, Rafael Canizares and A.
Kaplan, 2000, Geophys. Res. Let., accepted) are shown in Figs. F5 and F6. Predictions using linear
inverse modeling (Penland and Magorian 1993, J. Climate, 6, 1067-1076) are
shown in Figs. F7 and F8.
Predictions from the Scripps / Max Planck Institute (MPI) hybrid coupled model (Barnett et
al. 1993, J. Climate, 6, 1545-1566) are shown in Fig. F9.
The CPC and the contributors to the Forecast
Forum caution potential users of this predictive information that they can expect only
modest skill.
Outlook
A gradual transition to warm episode conditions is expected to continue in the tropical
Pacific through the first half of 2002.
Discussion
Most oceanic and atmospheric indices reflected ENSO-neutral conditions during September
(Tables T1, T2). However, over
the past two years there has been a gradual eastward shift of positive equatorial
subsurface temperature anomalies from the western equatorial Pacific into the central
equatorial Pacific (Fig. T15). This evolution is
consistent with the decay of the subsurface thermal structure that characterizes the
mature phase of cold episodes and the development of conditions usually found just prior
to warm (El Niņo) episodes. Consistent with this evolution, there has been a gradual
transition from negative to positive SST anomalies (Fig. T9)
and a gradual return to near normal low-level winds (Fig. T7)
in the central equatorial Pacific. The anomalously cool SSTs over the eastern equatorial
Pacific during September reflected the amplified annual cycle that has been observed in
that region since 1998 (Fig. T9).
Over the past several months the pattern of tropical convection [as inferred from
anomalous outgoing longwave radiation (OLR)] has been strongly modulated by tropical
intraseasonal (30-60 day) fluctuations associated with the Madden Julian Oscillation (MJO)
(Figs. T11, T12). Low-level wind
fluctuations across the central and western tropical Pacific were consistent with this
activity during the month (Fig. T13). In the past MJO
activity has been instrumental in producing low-level westerly wind bursts that are linked
to subsequent oceanic warming in the eastern equatorial Pacific during the onset phase of
warm episodes, especially during the transition seasons (March-May and
September-November). Since we are currently in a transition season, special attention will
be focused on the evolution of the MJO, and any effect that it has on surface and
subsurface ocean temperatures.
There is no clear consensus amongst the latest statistical and coupled model
predictions (Figs. F1, F2, F3, F4, F5, F6, F7, F8, F9). However, several of these predictions indicate that positive
SST anomalies will continue in the central equatorial Pacific through the first half of
2002. The impacts that this warming will have on global temperature and precipitation
patterns depend to a large degree on its intensity. At the moment, considering both the
SST predictions and the observed oceanic and atmospheric circulation patterns, it seems
most likely that the intensity of any warming will be weak or moderate.
Weekly updates of SST, 850-hPa wind, OLR, and the equatorial subsurface temperature
structure are available on the Climate Prediction Center homepage at:
http://www.cpc.ncep.noaa.gov (Weekly Update).
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