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

A gradual transition to warm episode conditions is expected to continue in the tropical Pacific during the remainder of 2001 and into the first half of 2002.

Discussion

Near-normal atmospheric and slightly warmer-than-normal oceanic conditions prevailed in the tropical Pacific during August. SST anomalies averaged less than 1°C at all locations in the tropical Pacific during the month (Fig. T18). However, SSTs and SST anomalies have steadily increased in the central equatorial Pacific since early 2001 rising to their highest levels since the 1997-1998 warm episode (Fig. T9). Accom-panying this evolution there has been a gradual return to near normal low-level winds throughout the equatorial Pacific (Fig. T7). The oceanic thermocline remained deeper-than-normal in the equatorial central and western Pacific (Fig. T15), with temperatures averaging up to 3°C above normal at thermocline depth (Fig. T17). Over the past two years there has been a gradual expansion of the area of positive equatorial subsurface temperature anomalies into the central Pacific (Fig. T15) and a gradual decrease in the strength and areal extent of the negative subsurface temperature anomalies in the eastern Pacific. This evolution is consistent with the decay of the subsurface thermal structure that characterizes the mature phase of cold episodes and the development of conditions usually found just prior to warm (El Niño) episodes.

The pattern of tropical convection [as inferred from anomalous outgoing longwave radiation (OLR)] was strongly modulated by tropical intraseasonal (30-60 day) fluctuations associated with the Madden Julian Oscillation (MJO) (Figs. T11, T12). Low-level wind fluctuations across the central and western tropical Pacific were consistent with this activity during the month (Fig. T13). In the past the MJO has been instrumental in producing low-level westerly wind bursts that are linked to subsequent oceanic warming in the eastern equatorial Pacific during the onset phase of warm episodes, especially during the transition seasons (March-May and September-November). Thus, special attention will be focused on the evolution of the MJO, and any effect that it has on surface and subsurface ocean temperatures over the next several months.

There is no clear consensus among the latest statistical and coupled model predictions. However, several of these predictions, including the NCEP statistical (Figs. F1 and F2) and coupled model forecasts (Figs. F3 and F4), indicate that positive SST anomalies will continue in the central equatorial Pacific during the remainder of 2001 and into the first half of 2002. The impacts that this warming will have on global temperature and precipitation patterns depend to a large degree on its intensity, areal extent, and location. At the moment, considering both the SST predictions and the observed oceanic and atmospheric circulation patterns, it seems most likely that the intensity of the warming will be weak or moderate.

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).