Forecast Forum - April 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.  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 ENSO-neutral to La Niña conditions is possible during the next 2-3 months.

Discussion     

           The pattern of anomalous sea surface temperatures (SSTs) during April 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 slightly positive in the Niño 4 and Niño 3.4 regions, slightly negative in the Niño 3 region and negative in the Niño 1+2 region (Table T2).  An area of anomalously warm SSTs persisted well west of the date line (near 150ºE) (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 generally 2°-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 reflect an evolution toward a Pacific cold (La Niña) episode. 

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 2007 is +0.1°C, which reflects ENSO-neutral conditions in the tropical Pacific.   Most of the statistical and coupled model forecasts, including those from the NCEP Climate Forecast System (CFS), indicate below-average SSTs in the tropical central and eastern Pacific during the next several months (Figs. F1, F2, F3, F4a, F4b, F5, F6, F7, F8, F9, F10, F11, F12 and F13).   Some forecast models, including the CFS, indicate a transition to La Niña during May-July 2007.  These forecasts are consistent with the observed evolution in atmospheric and oceanic conditions towards a Pacific cold episode. However, the spread of the most recent statistical and coupled model forecasts (ENSO-neutral to La Niña) indicates considerable uncertainty as to exactly when  La Niña might develop and how strong it might be.

            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/