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HOME > Expert Assessments > Climate Diagnostics Bulletin
Forecast Forum - May 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.


Based on the recent evolution of the observed oceanic surface and subsurface conditions and the SST predictions, it is likely that further development towards El Niņo will continue, with weak-to-moderate El Niņo conditions through early 2003.


Further evolution toward a Pacific basin-wide warm episode (El Niņo) was observed during May 2002, as sea surface temperature (SST) anomalies increased throughout the equatorial Pacific between 170°E and 95°W (Figs. T9, T18). By the end of May warmer-than-normal SSTs were observed throughout the western and central equatorial Pacific, with departures from average greater than +1°C in the region from 165°E to 135°W and also locally between 130°W and the South American coast. This warming represents a significant transition from the localized warmth (central equatorial Pacific and South American coast), observed during recent months (Fig. T9), toward a more extensive basin-wide warming typical of El Niņo/Southern Oscillation (ENSO) events.

The warming during May resulted from a significant weakening of the equatorial easterly winds throughout the Pacific related to the Madden-Julian Oscillation (MJO) (Fig. T13). The MJO is an important source of variability that can contribute to the evolution toward El Niņo through related fluctuations in low-level winds and precipitation over the western and central equatorial Pacific. An eastward-propagating oceanic Kelvin wave, initiated by strong MJO activity in late 2001 (Figs. T11, T12), resulted in the rapid warming that was observed along the coasts of Ecuador and northern Peru in early February (Fig. T9). Subsequently, MJO activity was relatively weak during early 2002, with no additional significant Kelvin wave activity. However, in late April 2002 the MJO intensified (Figs. T11, T12) and during the last half of May the low-level equatorial easterly winds substantially weakened throughout the Pacific (Fig. T13), accompanied by an increase in equatorial SST anomalies (Fig. T9). NOAA TAO buoy data indicate that the oceanic thermocline has deepened east of the date line (180°W) since mid-May, consistent with the basin-wide weakening of the low-level equatorial easterly winds. This deepening is an indication of renewed Kelvin wave activity. Given the recent strength of the MJO and its period of about 40 days, it is likely that significant month-to-month fluctuations will continue to occur in many atmospheric indices used to monitor the ENSO cycle. In spite of this variability, the overall trends in SSTs and some atmospheric indices (Southern Oscillation Index, 850-hPa zonal wind) in recent months indicate that further development towards El Niņo will continue (Tables T1 and T2).

This assessment agrees well with the latest statistical and coupled model predictions (Figs. F1, F2F3F4a,   F4bF5F6F7F8,   F9) which indicate weak-to-moderate El Niņo conditions through early 2003. Based on the recent evolution of the observed oceanic conditions and the SST predictions, it appears most likely that warming will continue over the next several months, and that weak-to-moderate El Niņo conditions will continue into early 2003. It is important to add that a weak or moderate El Niņo would feature much weaker global impacts than were experienced during the very strong 1997-98 El Niņo.

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).

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