Forecast Forum - May 2004

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. et al. 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. et al. 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.  Niño 3.4 predictions are summarized in F13, which is provided by the Forecasting and Prediction Research Group of the IRI.

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 observed atmospheric and oceanic conditions and recent trends, ENSO-neutral conditions are expected to continue for the next 3 months.

Discussion

Oceanic and atmospheric conditions in the Pacific basin continued to reflect the neutral phase of the ENSO cycle during May 2004.  Sea surface temperatures were warmer-than-average in the western and central equatorial Pacific (Niño 3.4 and 4 regions) and cooler-than-average in the eastern equatorial Pacific (Niño 3 and 1+2 regions) during the month (Table T2). 

Positive SST anomalies greater than +0.5°C (~1°F) were found between 130°E and 170°W, and in portions of the region between 170°W and 120°W, while negative SST anomalies less than          -0.5°C were found between 120°W and the South American coast (Figs. T9, T18).    

Over the past several months equatorial Pacific SST anomalies have been largest in the western Pacific, resulting in an enhanced east-west gradient of SST that has been associated with stronger-than-average easterly winds over the central equatorial Pacific (Figs. T13, T20) and enhanced precipitation over the western equatorial Pacific (Figs. T25, E3). These conditions are consistent with a steeper-than-average thermocline slope in the central equatorial Pacific, with positive (negative) subsurface temperature departures in the western (eastern) portion of the basin (Fig. T17).

Slightly more than half of the statistical and coupled model forecasts indicate near neutral conditions in the tropical Pacific (Niño 3.4 SST anomalies between -0.5°C and +0.5°C) through the northern summer and fall 2004 (Figs. F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, F12, F13).  The remaining forecasts indicate that El Niño conditions will develop within the next 3-6 months.   The increasing spread of the forecasts during the last half of 2004 indicates greater uncertainty.  Given the recent trends and observed oceanic and atmospheric patterns discussed above, it is more likely that ENSO-neutral conditions will continue for the next 3 months (through August 2004). There is considerable uncertainty about what will happen after August 2004.

Weekly updates of SST, 850-hPa wind, OLR and features of the equatorial subsurface thermal structure are available on the Climate Prediction Center homepage at: http://www.cpc.ncep.noaa.gov.