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Forecast Forum - December 1999

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 Cane and Zebiak model (Cane et al. 1986, Nature, 321, 827-832; Zebiak and Cane 1987, Mon. Wea. Rev., 115, 2262-2278) are shown in Figs. F5 and F6. Predictions from the modified Cane and Zebiak model (Chen et al. 1998, Geophys. Res. Let., 103, 2387-2840), referred to in the figures as LDEO3, are shown in Figs. F7 and F8. Predictions using linear inverse modeling (Penland and Magorian 1993, J. Climate, 6, 1067-1076) are shown in Figs. F9 and F10. Predictions from the Scripps / Max Planck Institute (MPI) hybrid coupled model (Barnett et al. 1993, J. Climate, 6, 1545-1566) are shown in Fig. F11.

The CPC and the contributors to the Forecast Forum caution potential users of this predictive information that they can expect only modest skill.

Discussion and Outlook

Cold episode conditions continued in the tropical Pacific during December, as equatorial sea surface temperatures (SSTs) remained well below normal across the central and east-central equatorial Pacific (Fig. T18 and Table T2). Negative subsurface temperature anomalies and a shallower than normal oceanic thermocline also continued to dominate the equatorial Pacific east of the date line, with the thermocline more than 30 m shallower than normal from 145W to 95W (Fig. T16). Accompanying these conditions, the mean low-level equatorial easterly winds were stronger than normal over the western and central tropical Pacific and near normal over the eastern Pacific (Fig. T20). Low-level easterly anomalies have been observed in the western and central equatorial Pacific since June 1998 (Fig. T7). At upper levels, enhanced westerlies were found over much of the central and eastern tropical Pacific during December, consistent with cold episode conditions (Fig. T21). Tropical convection was suppressed across the western and central equatorial Pacific and enhanced over Indonesia, and the Philippines (Fig. T25). This pattern has been very persistent for the past 19 months (Fig. T8), consistent with the ongoing cold episode.

Over the past several months the pattern of subsurface temperature anomalies has been very persistent, with positive anomalies in the western equatorial Pacific and negative anomalies in the eastern equatorial Pacific (Fig. T17). At the present time this pattern shows no sign of evolving toward a pre-warm episode state. Thus, it is likely that cold episode conditions will continue for the next several months. This assessment is supported by the most recent NCEP coupled model forecast (Figs. F3 and F4) and by other available coupled model and statistical model predictions that indicate cold episode conditions persisting through the first half of 2000.

Based on current conditions in the tropical Pacific, on the NCEP SST predictions, and on results from historical studies on the effects of cold episodes, we expect wetter-than-normal conditions to continue during the January-March period over Indonesia, northern Australia, southern Africa, and northeastern South America. Drier- and warmer-than-normal conditions are expected along the southern tier of the United States from New Mexico to the Carolinas.

Weekly updates of SST, 850-hPa wind and OLR are available on the Climate Prediction Center homepage at: http://www.cpc.ncep.noaa.gov (Weekly Update).


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