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Climate Diagnostics Bulletin

Forecast Forum - August 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 Markov model (Xue, Y., A. Leetmaa, and M. Ji, 2000: ENSO prediction with Markov model: The impact of sea level. J. Climate, 13, 849-871) are shown in Figs. F5 and F6.   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., 27, 2585-2587) 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.   Predictions from the ENSO-CLIPER statistical model (Knaff, J. A. and C. W. Landsea 1997, Wea. Forecasting, 12, 633-652) are shown in Fig. F12.

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


Based on the observed oceanic and atmospheric conditions and the SST predictions, moderate warm episode (El Niņo) conditions are expected to continue during the remainder of 2002 and into early 2003.


Warm episode (El Niņo) conditions prevailed during August 2002. Sea surface temperature (SST) anomalies (departures from average) remained greater than +1°C throughout the central equatorial Pacific between 175°E and 130°W (Fig. T18). Atmospheric indicators of a warm episode (El Niņo) include consistently negative values of the Southern Oscillation Index (SOI) since March 2002 (Table T1), and weaker-than-average low-level easterly winds since May 2002 throughout the equatorial Pacific (Fig. T7).

The Madden-Julian Oscillation (MJO) continues to be a major source of week-to-week and month-to-month variability in the atmospheric circulation of the Tropics and subtropics (Figs. T11, T12, T13). The MJO contributed to substantial weakening of the low-level easterly winds throughout the equatorial Pacific during early July and again during late August (Figs. T13, T20), helping to maintain positive subsurface temperature anomalies (Fig. T17) and a deeper-than-average oceanic thermocline (Figs. T15 and T16) throughout most of the equatorial Pacific.

The oceanic and atmospheric variables discussed above reflect the presence of moderate El Niņo conditions. This assessment is consistent with most coupled model and statistical model forecasts (Figs. F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, F12), which indicate that moderate El Niņo conditions are likely to continue through the end of 2002 and into early 2003. While SST anomalies in several of the models decrease in the first season and then remain above average in subsequent seasons (e.g. Figs. F2 and F6), those in other models increase in the first season (e.g. Fig. F8). Although there is considerable uncertainty in the forecasts about the timing and intensity of the peak of this warm episode, all of the forecasts indicate that it will be much weaker than the 1997-98 El Niņo. It is important to add that the global impacts of this warm episode should be correspondingly weaker than those observed during the very strong 1997-98 El Niņo.

Based on the current conditions in the tropical Pacific, on the SST predictions, and on results from historical studies of the effects of ENSO, we expect drier-than-average conditions to continue over Indonesia and eastern Australia during the next several months, and wetter-than-average conditions over southeastern South America during the next three months. Over North America drier-than-average conditions are expected in the Pacific Northwest and mid-Atlantic states during fall 2002 and in the northern Rockies and Ohio Valley states during winter 2002-2003. Wetter-than-average conditions are expected in the southern tier-of-states from central/ southern California to the Carolinas during winter 2002-2003, and warmer-than-average conditions are expected in the northern Great Plains, upper Midwest, southern/southeastern Alaska, and western and central Canada during late fall 2002 and winter 2002-2003.

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