Forecast Forum - October 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.  Ni�o 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

            ENSO-neutral or weak La Ni�a conditions are likely during the next 6-9 months.

Discussion

During October, equatorial SST anomalies greater than +0.5�C were found between Indonesia and 170�W, while negative anomalies less than �0.5�C were observed at most locations between 130�W and the South American coast (Figs. T9 and T18).  The SST departures in the Ni�o 3, and Ni�o 1+2 regions were negative, while weak positive departures were observed in the Ni�o 4 and Ni�o 3.4 regions (Table T2 and Fig. T5).  During the last three months surface and subsurface temperature anomalies decreased, especially in the eastern equatorial Pacific(Figs. T9, T15 and T17), and the Southern Oscillation Index (SOI) increased (Fig. T2). During the same period persistent stronger-than-average low-level equatorial easterly winds were observed over the central Pacific (Figs. T7 and T13), while near-average patterns of convection (Figs. T8 and T25) and sea level pressure (Figs. T10 and T19) occurred over most of the tropical Pacific.  Collectively, the present oceanic and atmospheric anomalies are consistent with ENSO-neutral conditions in the tropical Pacific.

           The value of the Oceanic Ni�o Index (ONI; 3-month running mean average of SST anomalies in the Ni�o 3.4 region � computed using the Extended Reconstructed SST version-2 data set) for August-October 2005 is 0.0�C, which indicates ENSO neutral conditions.  The spread of the most recent statistical and coupled model forecasts (weak La Ni�a to weak El Ni�o) indicates some uncertainty in the outlooks (Figs. F1, F2, F3, F4a, F4b, F5, F6, F7, F8, F9, F10, F11, F12 and F13). However, current conditions (stronger-than-average easterly winds over the central equatorial Pacific) and recent observed trends (decreasing SST anomalies throughout the central and eastern equatorial Pacific) do not support the development of El Ni�o. Rather, they support either a continuation of ENSO-neutral conditions or the development of weak La Ni�a conditions during the next 6-9 months.