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HOME > Expert Assessments > Climate Diagnostics Bulletin

Forecast Forum - March 2000

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 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 sea surface temperatures (SSTs) remained 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 (Fig. T16) continue to dominate the equatorial Pacific east of 140° W, although the magnitude of the anomalies has decreased from those observed earlier in the year (Fig. T15). Accompanying these conditions, the mean low-level equatorial easterly winds remained much stronger than normal over the west-central and central tropical Pacific and slightly weaker than normal over the eastern Pacific (Fig. T20). Enhanced low-level westerlies were observed over the eastern Indian Ocean and Indonesia. This pattern of low-level winds contributed to enhanced low-level convergence and precipitation, as inferred from the anomalous Outgoing Longwave Radiation (OLR), over Indonesia, the Philippines and northwestern Australia and suppressed precipitation in the equatorial central Pacific (Fig. T25). These patterns of anomalous convection and low-level winds have been highly persistent since the summer of 1998 (Figs. T7 and T8 ), consistent with ongoing cold episode conditions.

Since December 1999 there has been a slow eastward expansion of the positive subsurface anomalies into the central Pacific, which is consistent with a slow evolution of the subsurface thermal structure toward a pre-warm episode state. Historically, this "build-up" phase of the ENSO cycle has lasted between one and two years before the subsequent development of warm episode conditions.

The latest NCEP coupled model and statistical model forecasts and other available forecasts all indicate a weakening of La Niņa conditions during the next 3-6 months. The NCEP coupled model forecast (Figs. F3 and F4) continues to indicate that cold episode conditions will weaken during the next 3 months, followed by a return to near-normal conditions during the remainder of the year. The NCEP statistical model forecast (Figs. F1 and F2) also shows a return to near normal conditions, but during July–September, while the other available coupled model and statistical model predictions (Figs. F9, F10, F11) indicate a gradual weakening of cold episode conditions and a return to near-normal conditions by early 2001. The NCEP statistical model is now the only forecast that develops warm episode conditions, and this technique has delayed the onset of El Niņo conditions to early 2001. Thus, it is expected that cold episode conditions will weaken over the next 3-6 months and that near-normal or slightly cooler-than-normal conditions will be present by the end of the year.

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

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