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Forecast Forum - June 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

Near-normal or slightly warmer-than-normal conditions are expected in the tropical Pacific into early 2002

Discussion

Near-normal atmospheric and oceanic conditions prevailed in the tropical Pacific during June. SST anomalies averaged less than 1C at all locations in the tropical Pacific except along the immediate South American coast where negative anomalies of around -1C were found (Fig. T18). The oceanic thermocline remained deeper-than-normal in the equatorial west-central and western Pacific (Fig. T15), with temperatures averaging up to 4C above normal at thermocline depth (Fig. T17). The negative temperature anomalies that have characterized the subsurface thermal structure in the eastern Pacific since late 1998 have continued to weaken (Fig. T15). The pattern of anomalous tropical convection [as inferred from anomalous outgoing longwave radiation (OLR)] was rather disorganized during the month, with areas of above-normal precipitation over Indonesia and along the South Pacific Convergence Zone (SPCZ), and below-normal precipitation near the date line (Fig. T25). Consistent with this, the low-level winds across the central and western tropical Pacific were weak (Fig. T20).

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). SST’s near the international date line have gradually warmed and are now slightly warmer-than-normal for the first time since the 1997-98 El Nio (Figs. T5, T9). This evolution is consistent with a decay of the subsurface thermal structure that characterizes the mature phase of cold episodes towards a pre-warm episode state. Thus, it is likely that near-normal or slightly warmer-than-normal conditions will persist for the remainder 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, F9), which indicate near-normal or slightly warmer-than-normal conditions into early 2002.

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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