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Forecast Forum - November 2001

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 over the next several months.

Discussion

Most oceanic and atmospheric indices reflected a continuation of ENSO-neutral conditions during November (Tables T1, T2). However, there are indications of a slow evolution towards a warm episode. Since June 2001 sea surface temperatures (SSTs) have become anomalously warm in the central equatorial Pacific, with anomalies near 1°C just to the west of the date line (Fig. T9). During the same period subsurface temperature anomalies remained positive in the central equatorial Pacific (Fig. T15), indicating a deeper-than-normal thermocline in that region. Similar patterns have been observed immediately prior to the onset of warm episodes.

In recent months, many tropical Pacific atmospheric and oceanic variables have been strongly modulated by tropical intraseasonal (30-60 day) fluctuations associated with the Madden Julian Oscillation (MJO). Low-level wind fluctuations over the central and western tropical Pacific have been consistent with this activity (Fig. T13). In the past, the convectively active phase of the MJO 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). A significant westerly wind burst occurred over the western equatorial Pacific during mid-October (Fig. T13). November featured stronger-than-normal easterlies during much of the month, followed by westerly anomalies near the end of the month.

The majority of the latest statistical and coupled model predictions (Figs. F1, F2, F3, F4, F5, F6, F7, F8, F9) indicate either weak warm or near-normal conditions in the equatorial Pacific during the next three to six months. However, all of these prediction techniques have difficulty in making skillful forecasts during ENSO transitions. Considering the SST predictions, the time of year, and the observed oceanic and atmospheric circulation patterns, it seems most likely that a gradual evolution to warm episode conditions will continue in the tropical Pacific over the next several months.

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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