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Forecast Forum - March 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 March. As in previous months, sea surface temperatures (SSTs) were well below normal across the central and east-central equatorial Pacific (Fig. T18 and Table T2). Negative subsurface temperature anomalies (Fig. T17) and a shallower than normal oceanic thermocline continue to dominate the equatorial Pacific with the thermocline more than 30 m shallower than normal from 150° W to 115° W (Fig. T16). Accompanying these conditions, the mean low-level equatorial easterly winds remained much stronger than normal over the central tropical Pacific and near normal over the eastern Pacific (Fig. T20). At upper levels, enhanced westerlies were found over much of the central tropical Pacific (Fig. T21). These conditions contributed to a vigorous Walker circulation over the equatorial western and central Pacific (Fig. T29). The pattern of anomalous precipitation as inferred from the anomalous Outgoing Longwave Radiation (OLR), indicated enhanced convection over the eastern Indian Ocean, Indonesia, and the Philippines and suppressed convection over the remainder of the equatorial Pacific east of New Guinea (Fig. T25). This pattern has been very persistent since SeptemberNovember 1998 (Fig. T8 ), consistent with cold episode conditions.

The latest NCEP statistical (Figs. F1 and F2 ) and coupled model forecasts (Figs. F3 and F4) indicate that cold episode conditions in the tropical Pacific will likely continue for the next three months. Other statistical and coupled model forecasts are consistent with the NCEP models through this period. The dynamical and statistical model forecasts exhibit considerable variability thereafter, which is also a period of climatologically low skill.

Weekly updates of SST, 850-hPa wind and OLR are available on the Climate Prediction Center homepage at: (La Niña / Weekly Update).

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