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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 early 2002.
Discussion
Near-normal atmospheric and slightly warmer-than-normal oceanic conditions prevailed in
the tropical Pacific during July. SST anomalies averaged less than 1°C at all locations in the tropical Pacific during the
month (Fig. T18). However, SSTs and SST anomalies have
steadily increased in the central equatorial Pacific since early 2001 (Fig.
T9) rising to their highest levels since the 1997-1998 warm episode by late July.
The oceanic thermocline remained deeper-than-normal in the equatorial central and western
Pacific (Fig. T15), with temperatures averaging around 3°C above normal at thermocline depth (Fig. T17). Over the past two years there has been a gradual
eastward expansion of the area of positive subsurface temperature anomalies into the
central Pacific (Fig. T15) and a gradual decrease in the
strength and areal extent of the negative subsurface temperature anomalies in the eastern
Pacific. This evolution is consistent with a decay of the subsurface thermal structure
that characterizes the mature phase of cold episodes and with the development of
conditions usually found just prior to warm episodes. The pattern of anomalous tropical
convection [as inferred from anomalous outgoing longwave radiation (OLR)] was rather
disorganized during the month, with areas of below-normal precipitation extending from
Indonesia to the date line (Figs. T25, E4).
Consistent with this, the low-level wind anomalies across the central and western tropical
Pacific were weak (Fig. T20).
Positive SST anomalies are likely to continue in the equatorial Pacific during the
remainder of 2001 and the first half of 2002. This assessment is generally consistent with
the most recent NCEP statistical (Figs. F1 and F2) and coupled model forecasts (Figs. F3
and F4), as well as most other coupled model and statistical
model predictions (Figs. F5, F6, F7, F8, F9) that
indicate warmer-than-normal oceanic conditions through early 2002. The impacts that this
warming will have on global temperature and precipitation patterns depend to a large
degree on its intensity, areal extent, and location. There is considerable spread in the
predicted SST anomalies, with most predictions indicating a weak or moderate warm episode
(El Niño) by the end of 2001 and the beginning of 2002.
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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www.nws.noaa.gov
