Forecast Forum - May 2007

          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

            A transition from ENSO-neutral to La Ni�a conditions is possible during the next 1-3 months.

Discussion     

           The pattern of anomalous sea surface temperatures (SSTs) during May 2007 was consistent with ENSO-neutral conditions in the tropical Pacific, with average to below-average SSTs extending from the date line to the west coast of South America (Fig. T18).  The latest SST departures are negative in the Ni�o 1+2 (-1.6�C) and Ni�o 3 (-0.7 �C) regions, and remain near zero in the Ni�o 3.4 (-0.2 �C) and Ni�o 4 (+0.2 �C) regions (Table T2).  An area of anomalously warm SSTs persisted well west of the date line (near 150�E) (Fig. T18).  

The equatorial upper-ocean heat content (average temperature departures in the upper 300 m of the ocean) remained below-average across the central and east-central equatorial Pacific, with temperatures at thermocline depth ranging from 1�- 4�C below average (Fig. T17).  Consistent with the surface and sub-surface temperature patterns, stronger than-average low-level easterly winds persisted over the central equatorial Pacific (Figs. T7 and T20), and convection was enhanced over the western equatorial Pacific and suppressed east of the date line (Fig. T25). Collectively, these atmospheric and oceanic conditions continue to indicate that La Ni�a conditions could develop over the next 1-3 months.   

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 March � May 2007 is -0.1�C, which reflects ENSO-neutral conditions in the tropical Pacific.  Nearly all of the model forecasts predict below-average SSTs in the Ni�o 3.4 region (5�N-5�S, 120-170�W) during the remainder of the year (Figs. F1, F2, F3, F4a, F4b, F5, F6, F7, F8, F9, F10, F11, F12 and F13).   Most statistical models show ENSO-neutral conditions persisting through August 2007, while most dynamical models indicate La Ni�a will develop within the next three months.  Some forecast models, especially the NCEP Climate Forecast System (CFS), continue to predict a rapid transition to La Ni�a conditions.  However, for the past few months the CFS forecasts have been predicting a stronger and more rapid cooling than has actually occurred.  Historically, the next few months are a favorable period for the development of La Ni�a.

            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/