Forecast Forum - November  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 warmer-than-average (borderline weak El Ni�o and ENSO-neutral) conditions will persist in the equatorial Pacific through the Northern Hemisphere winter of 2003-2004.

Discussion

Surface and subsurface temperatures remained warmer than average across most of the equatorial Pacific Ocean during November. Equatorial ocean surface temperatures greater than +0.5�C (~1�F) above average were found in most areas between Indonesia and the South American coast (Fig. T9), while departures greater than +1�C were found between 150�E and 170�W (Fig. T18). Positive SST anomalies were observed in all four Ni�o index regions for the second consecutive month (Table T2). Positive equatorial upper-ocean temperature departures persisted throughout the equatorial Pacific during November (Figs. T15, T17). Overall the basin-wide upper ocean heat content was 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, all of the atmospheric indices typically used to monitor ENSO remained near zero during November (Table 1), indicating a continuation of ENSO-neutral atmospheric conditions. 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.

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 Northern Hemisphere 2003-2004 winter (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, which is consistent with observed trends in SST anomalies in the vicinity of the date line. The three-month (September-November) average SST anomaly in the Ni�o 3.4 region (+0.4�C) is just below the threshold (+0.5�C) required for NOAA to declare a weak Pacific warm episode (El Ni�o). It is likely that the October-December 2003 average will reach that threshold and that borderline weak El Ni�o / ENSO-neutral conditions will persist through the winter. However, it seems unlikely that classical El Ni�o conditions will develop along the west coast of South America.

In the past, weak Pacific warm episodes have not shown consistent temperature and precipitation impacts for areas outside the tropical Pacific. Therefore, at this time these conditions are not expected to have any significant impacts on wintertime 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.