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.

Near-normal conditions are likely in the tropical Pacific during Northern Hemisphere summer, followed by near-normal or slightly warmer-than-normal conditions into early 2002.

Discussion

The large-scale oceanic and atmospheric circulation patterns were consistent with weak cold episode conditions in the tropical Pacific during April. Negative SST anomalies continued to weaken across the central tropical Pacific during the month (Figs. T9, T18). The anomalously warm SSTs that were present over most of the eastern tropical Pacific during February and March 2001 have weakened as cross-equatorial flow became established over the region during April. A similar evolution was observed in each of the last three years (Fig. T9). The slope of the oceanic thermocline remained greater than normal, with positive subsurface temperature anomalies in the western and central equatorial Pacific and negative anomalies in the eastern Pacific (Figs. T16 and T17). Cold episode related atmospheric features included stronger-than-normal low-level easterly winds over the western tropical Pacific (Fig. T20), above-normal precipitation over Indonesia (Fig. T25), and suppressed rainfall near the date line (Fig. T25). Overall, the patterns of anomalous 850-hPa zonal wind and convection have shown remarkable similarity over the central equatorial Pacific during the last three years, with a distinct annual cycle featuring maxima in the low-level easterly winds (Fig. T7) and maxima in the OLR anomalies (Fig. T8) during the northern winter seasons.

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). This evolution is consistent with a slow decay of the subsurface thermal structure that characterizes the mature phase of cold episodes. Thus, it is likely that cold episode conditions will continue to weaken, with near-normal conditions likely during the summer of 2001. This assessment is generally supported by the most recent NCEP statistical (Figs. F1 and F2) and coupled model forecasts (Figs. F3 and F4), as well as by other available coupled model and statistical model predictions (Figs. F5, F6, F7, F8, and F9), which indicate near-normal conditions during Northern Hemisphere summer. Thereafter, the models indicate near-normal or slightly warmer-than-normal conditions into early 2002.