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Forecast Forum - August 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

The overall patterns of oceanic temperatures and atmospheric circulation during August were consistent with strengthening cold episode conditions. Sea surface temperatures (SSTs) remained below normal throughout the equatorial Pacific east of 160E, with negative anomalies exceeding -1C between 170W and 120W (Fig. T18 and Table T2). Accompanying these conditions, weaker-than-normal convection (Fig. T25) prevailed throughout the equatorial Pacific east of 160E, and low-level easterlies remained stronger-than-normal between 150E and 150W (Fig. T20). Consistent with the negative SST anomalies, the oceanic thermocline remained shallower than normal in the eastern equatorial Pacific and deeper than normal in the western equatorial Pacific (Fig. T16). Subsurface temperature anomalies near 130W averaged as much as 5C below normal (Fig. T17) for the first time since March 1999.

The positive subsurface temperature anomalies in the west-central equatorial Pacific continue to show little evidence of an eastward shift indicating that cold episode conditions are likely to persist in the tropical Pacific for at least the next several months. This assessment is supported by the most recent NCEP coupled model forecast (Figs. F3 and F4) and other available coupled model and statistical model predictions that indicate cold episode conditions persisting through the Northern Hemisphere spring of 2000.

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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