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Forecast Forum - April 2006

          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.


            ENSO-neutral conditions are expected during the next 3-6 months. 


           The patterns of anomalous ocean temperatures are consistent in indicating a return to ENSO-neutral conditions in the tropical Pacific. During April SSTs were close to average at most locations between Indonesia and 90oW (Fig. T18), which is reflected in the near zero departures observed in all of the Niño regions, except for Niño 1+2 (Table T2 and Fig. T5). During the month, negative SST departures developed in the extreme eastern equatorial Pacific (Fig. T18), which is a reversal from conditions observed during February-March (Table T2).

           During April above-average precipitation (negative OLR anomalies) was observed over portions of Indonesia and northern Australia, while below-average precipitation (positive OLR anomalies) was observed over the central equatorial Pacific and the eastern tropical Pacific between the equator and 20ºN (Fig. T25).  Slightly stronger-than-average low-level (850-hPa) easterly winds persisted over the central equatorial Pacific (Figs. T7 and T20), and anomalous upper-level (200-hPa) cyclonic circulation centers were observed in both hemispheres (Fig. T22).  Although these atmospheric features are lingering effects of the La Niña, they are weaker than in previous months. The equatorial subsurface temperature anomaly pattern featured negative anomalies in the eastern Pacific and positive anomalies in the western and central Pacific during April 2006 (Fig. T17).  Since February the area of positive anomalies at depth has expanded to the east (Fig. T15), and the basin-wide upper ocean heat content has increased. Collectively, these atmospheric and oceanic features are consistent in indicating the demise of La Niña and a return to ENSO-neutral conditions.

           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 February - April 2006 is -0.4°C, which indicates ENSO neutral conditions.  Most of the statistical  and coupled model forecasts indicate ENSO-neutral conditions in the tropical Pacific through the end of 2006 (Figs. F1, F2, F3, F4a, F4b, F5, F6, F7, F8, F9, F10, F11, F12 and F13). The spread of these forecasts (weak La Niña to weak El Niño) indicates considerable uncertainty in the outlook for the last half of the year.

            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:


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