Forecast Forum - August 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 likely through the end of 2006 and into early 2007.

Discussion

By early September equatorial SST anomalies greater than +0.5ºC were observed in most of the equatorial Pacific, with anomalies exceeding +1.0ºC in the central Pacific between 165ºE and 170ºW (Fig. T18).  The latest SST departures in the Niño regions are all greater than +0.5 (Table 2, Fig. T5).  Beginning in February the basin-wide upper ocean heat content increased, and since early April positive anomalies have been observed.  Since early July weaker-than-average low-level equatorial easterly winds have been observed across most of the equatorial Pacific (Fig. T20). In August the Southern Oscillation Index (SOI) was negative for the fourth consecutive month (Fig. T1). Collectively, these oceanic and atmospheric anomalies are consistent with developing warm episode (El Niño) conditions in the tropical Pacific. 

Over the past several months most of the statistical and coupled model forecasts have trended towards warmer conditions in the tropical Pacific through the Northern Hemisphere winter.  The latest NCEP coupled forecast system (CFS) predictions indicate El Niño conditions for the remainder of 2006 and into the NH spring 2007.  More than half of the other statistical and coupled model predictions are also favoring El Niño conditions during the same period (Figs. F1, F2, F3, F4a, F4b, F5, F6, F7, F8, F9, F10, F11, F12 and F13). The recent conditions (weaker-than-average easterly winds over the central equatorial Pacific) and warming trends in observed oceanic conditions support these predictions.

Some impacts from the developing El Niño are already evident in the pattern of tropical precipitation. During the last 30 days drier-than-average conditions have been observed across all of Indonesia , Malaysia and the Philippines , which are usually the first areas to experience ENSO-related impacts. This dryness can be expected to continue, on average, for the remainder of 2006.  

Typical El Niño effects are likely to develop over North America during the upcoming winter season. Those include warmer-than-average temperatures over western and central Canada , and over the western and northern United States . Wetter-than-average conditions are likely over portions of the U.S. Gulf Coast and Florida , while drier-than-average conditions can be expected in the Ohio Valley and the Pacific Northwest . 

            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/