Forecast Forum - December 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.

Outlook

            El Niño conditions are likely to continue through March-May 2007.

Discussion     

Equatorial Pacific SST anomalies greater than +1ºC were observed in most of the equatorial Pacific between 170ºE and the South American coast during December (Fig. T18).  The latest SST departures in the Niño regions are around 1.0ºC, except near 0.5ºC for Niño 1+2 (Table T2, Fig. T5).  The increase in SST anomalies during the last several months has been accompanied by weaker-than-average low-level equatorial easterly winds across most of the equatorial Pacific (Fig. T13) and negative values of the Southern Oscillation Index (SOI) (Table T1; Fig. T1). Collectively, these oceanic and atmospheric anomalies indicated the development of El Niño in the tropical Pacific. 

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 October-December 2006 is +1.1°C, which indicates El Niño conditions.  Most of the statistical and coupled models indicate that SST anomalies are near their peak and that decreasing anomalies are likely during early 2007 (Figs. F1, F2, F3, F4a, F4b, F5, F6, F7, F8, F9, F10, F11, F12 and F13), with the NCEP Climate Forecast System (CFS) indicating a rapid weakening in the next month.  Recent observed trends in the upper ocean tend to support those forecasts.  This is a significant change from just a few weeks ago when a number of the forecast tools were indicating the persistence or even increases in SST anomalies during this period.  The large spread in the most recent set of forecasts indicates that there is considerable uncertainty in this outlook.  A resurgence of MJO activity in late December 2006 has the potential to trigger a more persistent pattern of cloudiness and precipitation over the anomalously warm waters of the central equatorial Pacific during the next several weeks. If that occurs, then the equatorial easterlies over the central Pacific will likely weaken possibly leading to a continuation of El Niño conditions beyond that which is currently indicated by the CFS.  Please refer to the ENSO Evolution, Status and Prediction Presentation available on the CPC El Niño/ La Niña page for weekly updates on the latest conditions in the tropical Pacific (see link below).

There is an increased probability of observing El Niño-related effects over North America during January-March 2007, including warmer-than-average temperatures over western and central Canada , and over the northern United States , wetter-than-average conditions over portions of the U.S. Gulf Coast and Florida , and drier-than-average conditions in the Ohio Valley and in portions of the Pacific Northwest . Global effects that can be expected during January-March include drier-than-average conditions over portions of Malaysia, Indonesia, northern and eastern Australia, some of the U.S.-affiliated islands in the tropical North Pacific, northern South America and southeastern Africa, and wetter-than-average conditions over central South America (Uruguay, northeastern Argentina, southeastern Paraguay and southern Brazil) and possibly along the coasts of Ecuador and northern Peru. 

            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/