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Forecast Forum - February 2002

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 F4a, F4b. 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.   Predictions from the ENSO-CLIPER statistical model (Knaff, J. A. and C. W. Landsea 1997, Wea. Forecasting, 12, 633-652) are shown in Fig. F10.

The CPC and the contributors to the Forecast Forum caution potential users of this predictive information that they can expect only modest skill.

Outlook

Based on the observed oceanic and atmospheric circulation patterns and their recent evolution, the SST predictions, and the time of year, it seems likely that warm-episode (El Nio) conditions will develop in the tropical Pacific during the next 3 months and persist during the remainder of 2002.

Discussion

The evolution towards warm-episode conditions in the tropical Pacific continued during February 2002. Warmer-than-normal sea surface (Fig. T9) and subsurface (Fig. T15) temperatures developed across the equatorial Pacific during the month. By late in the month equatorial SST anomalies exceeded +1C in the vicinity of the date line (Fig. T18) and in the extreme eastern equatorial Pacific near the South American coast. The warming of surface and subsurface waters along the South American coast was due to the arrival of an oceanic Kelvin wave that has been propagating eastward from the central equatorial Pacific since mid-December. The Kelvin wave contributed to a substantial deepening of the oceanic thermocline from the dateline eastward to the South American coast during January and February 2002 (Fig. T15). These conditions are often observed in the early stages of El Nio.

Atmospheric indices are giving mixed signals concerning the evolution toward warm-episode (El Nio/ Southern Oscillation - ENSO) conditions (Table T1). Those indices not yet supporting a developing El Nio include the Southern Oscillation Index (Tahiti-Darwin SOI), the low-level easterlies over the central equatorial Pacific, and the upper-tropospheric (200-hPa) winds. In contrast, enhanced rainfall has been observed over the tropical west-central Pacific, from Papua New Guinea eastward to the date line (180W) since the beginning of 2002 (Figs. T11, T25), and in late February enhanced rainfall also developed over the warmer-than-normal waters between the west coast of South America and the Galapagos Islands. These features reflect the warming in the sea surface temperatures, and are possibly the first atmospheric effects of a developing El Nio.

The latest statistical and coupled model predictions (Figs. F1, F2, F3, F4, F5, F6, F7, F8, F9, F10) show a spread from slightly cooler-than-normal conditions to moderate warm-episode conditions during the remainder of 2002. The coupled models and some statistical techniques that incorporate subsurface oceanic conditions indicate a slow evolution to weak or moderate warm-episode (El Nio) conditions during the next several months. Other techniques indicate that conditions will remain near normal or even return to slightly colder than normal for the remainder of 2002. The recent evolution in oceanic conditions supports the forecasts of a continued evolution toward El Nio.

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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