Forecast Forum - MAY 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 to dominate the tropical Pacific oceanic and atmospheric circulation during May. Sea surface temperature (SST) anomalies decreased in the central equatorial Pacific (Table T2), but the overall pattern remained similar to that observed in recent months (Figs. T9, T18). The pattern of equatorial subsurface temperature anomalies has also been highly persistent, with negative temperature anomalies in the upper ocean throughout the region east of the date line and positive anomalies in the western Pacific below about 50 m depth (Fig. T17). The positive subsurface temperature anomalies have shown little evidence of an eastward shift in recent months, consistent with the continuation of cold episode conditions.

The pattern of tropical convection during May (as inferred from Outgoing Longwave Radiation (OLR) measured by NOAA's polar-orbiting satellites) was again suppressed over the western and central equatorial Pacific and enhanced over Indonesia/ Malaysia and the Philippines (Fig. T25). This pattern of tropical convection is consistent with the pattern of low-level (850-hPa) winds, which show easterly anomalies over the central and west-central tropical Pacific and near normal winds over the eastern Pacific (Fig. T20).

The latest NCEP coupled model forecast (Figs. F3 and F4) maintains present cold episode conditions in the tropical Pacific through August 1999 followed by strengthening cold episode conditions into early 2000. The NCEP statistical model forecast (Figs. F1 and F2) maintains present cold episode conditions through the same period. Other statistical and coupled model forecasts are generally consistent with the NCEP forecasts through the remainder of 1999.

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).