Forecast Forum - December  2003

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 ocean/atmosphere model (Ji et al. 1998, Mon. Wea. Rev, 126, 1022-1034) are presented in Figs. F3 and F4a, F4b.  Predictions from the Markov model (Xue, Y. et al. 2000: ENSO prediction with Markov model: The impact of sea level. J. Climate, 13, 849-871) are shown in Figs. F5 and F6.   Predictions from the latest version of the LDEO model (Chen, D. 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, J. A. and C. W. Landsea 1997, Wea. Forecasting, 12, 633-652) are shown in Fig. F12.  Ni�o 3.4 predictions are summarized in F13, which is 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

Based on current conditions and recent observed trends, it is likely that slightly warmer-than-average conditions will persist in the equatorial Pacific into the Northern Hemisphere early spring 2004.

Discussion

Surface and subsurface temperatures remained warmer than average across most of the equatorial Pacific Ocean during December. Equatorial ocean surface temperatures more than +0.5�C (~1�F) above average were found in many areas between Indonesia and the South American coast (Fig. T9), while departures greater than +1�C were found between 160�E and 180�W (Fig. T18). Positive SST anomalies were observed in all four Ni�o index regions for the third consecutive month (Table T2). Positive equatorial upper-ocean temperature departures persisted throughout the equatorial Pacific during December (Figs. T15, T17). Overall the basin-wide upper ocean heat content was slightly greater than average during the month (Fig. T17).

At the moment there are no discernable impacts from the anomalously warm waters on the atmospheric circulation. In fact, none of the atmospheric indices typically used to monitor ENSO reflect warm episode conditions (Table T1). Over the past few months, these atmospheric indices have not shown any significant trends that would support either additional large-scale increases or any substantial decreases of SST anomalies in the equatorial Pacific. However, many of these indices have exhibited considerable week-to-week variability during late November and December in response to tropical intraseasonal (Madden-Julian Oscillation) activity. Wetter-than-average conditions, observed over the Indian Ocean in late November, shifted eastward to the western Pacific by late December (Fig. T11). At the same time, the equatorial easterlies weakened over the western Pacific and westerly anomalies developed in that region (Fig. T13). NOAA�s Climate Prediction Center will continue to monitor these features to determine what, if any, impacts this activity will have on surface and subsurface temperatures in the region between the date line and the South American coast.

A majority of the statistical and coupled model forecasts indicate near-average conditions in the equatorial Pacific (Ni�o 3.4 SST anomalies between -0.5�C and +0.5�C) through the early Northern Hemisphere spring 2004 (Figs. F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, F12, F13). However, some forecasts indicate weak El Ni�o conditions developing during the winter and intensifying thereafter. The three-month (October-December) average SST anomaly in the Ni�o 3.4 region (+0.5�C) is at the threshold (+0.5�C) required for NOAA to declare a weak Pacific warm episode (El Ni�o). However, the SST indices all decreased slightly during December and the atmospheric indices do not currently reflect warm episode conditions. Based on current conditions and recent observed trends, it is likely that slightly warmer-than-average conditions will persist in the equatorial Pacific into the Northern Hemisphere early spring 2004. These conditions are not expected to have any significant impacts on winter/early spring temperature and precipitation patterns over the United States.

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.