Forecast Forum - March 2005

          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 Forecast System Model (CFS03) are presented in Figs. F3 and F4a, F4b.  Predictions from the Markov model (Xue, et al. 2000: J. Climate, 13, 849‑871) are shown in Figs. F5 and F6.   Predictions from the latest version of the LDEO model (Chen 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 and Landsea 1997, Wea. Forecasting, 12, 633‑652) are shown in Fig. F12.  Niño 3.4 predictions are summarized in Fig. F13, 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

            A transition from weak warm-episode (El Niño) conditions to ENSO-neutral conditions is expected during the next three months.

Discussion

     Sea surface temperature (SST) anomalies increased in the Niño 3.4 and Niño 3 regions during March 2005 (Table T2). Positive SST anomalies greater than +1.0°C were observed in portions of the central and west central equatorial Pacific between 165°E and 165°W (Fig. T18). Cloudiness and precipitation returned to near average over Indonesia (Fig. T25), while the enhanced precipitation, observed over the central tropical Pacific in February, weakened and drier-than-average conditions developed over that region (Fig. T11).

     The increase in SST anomalies and upper-ocean heat content (Fig. T15) in the east-central equatorial Pacific during the last half of March was associated with an eastward-propagating oceanic Kelvin wave (downwelling phase) (Fig. T17). This wave is stronger than those that have occurred in recent months in association with MJO activity. Surface and subsurface ocean temperatures are expected to increase along the west coast of South America (Ecuador and northern Peru) during April 2005. However, substantial cooling in the upper ocean has occurred in the wake (upwelling phase) of this Kelvin wave (Fig. T17), accompanied by a strengthening of the easterly winds over the central and western equatorial Pacific during March (Fig. T20). This cooling is expected to propagate eastward, eventually reaching the eastern equatorial Pacific during May. Thus, the effects of the expected warming along the west coast of South America during April should be brief.

     The value of the Oceanic Niño Index (ONI; 3-month running mean average of SST anomalies in the Niño 3.4 region – computed using the Extended Reconstructed SST version-2 data set) for January-March 2005 is +0.5°C, which satisfies the NOAA operational definition of El Niño. However, a majority of the statistical and coupled model forecasts (Figs. F1, F2, F3, F4a, F4b, F5, F6, F7, F8, F9, F10, F11, F12 and F13) indicate that a transition from weak warm-episode (El Niño) conditions to ENSO -neutral conditions will continue during the next three months, and that ENSO-neutral conditions will likely prevail during the northern summer.

     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/