Forecast Forum - October  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 conditions (borderline El Ni�o/ ENSO-neutral) will persist in the equatorial Pacific through the Northern Hemisphere winter of 2003-04.

Discussion

Oceanic conditions were warmer-than-average across most of the equatorial Pacific during October 2003, with SST anomalies greater than +0.5�C (~1�F) prevailing between Indonesia and the South American coast (Figs. T9, T18). By the end of the month, positive SST anomalies were observed in all four of the Ni�o index regions (Table T2). Positive equatorial upper-ocean temperature departures persisted in the central and east-central equatorial Pacific (Figs. T15, T17). Overall the basin-wide upper ocean heat content was warmer-than-average during the month (Fig. T17). Generally, atmospheric conditions in the tropical Pacific have been near average in recent months (Table T1), with no significant trends that would support either additional large-scale increases or decreases of SST anomalies in the equatorial Pacific.

A majority of the statistical and coupled model forecasts indicate near neutral conditions in the tropical Pacific (Ni�o 3.4 SST anomalies between -0.5�C and +0.5�C) for the remainder of 2003 and early 2004 (Figs. F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, F12, F13). However, over the past few months there has been a trend in the suite of forecasts towards somewhat warmer conditions, which is consistent with observed trends in SST anomalies. The SST anomalies in the Ni�o 3.4 region were +0.3�C in September and +0.6�C in October (Table 2). If the October value persists through November, then the three-month (September-November) running mean index value would reach the threshold of +0.5�C required for NOAA to declare a weak El Ni�o. At this point it appears likely that borderline El Ni�o/ ENSO-neutral conditions will persist in the equatorial Pacific through the Northern Hemisphere winter of 2003-04. However, further evolution of warm-episode (El Ni�o) conditions is possible if persistent enhanced equatorial convection (cloudiness and rainfall) and weaker-than-average low-level easterly winds develop in the vicinity of the anomalously warm waters near the date line (180�W).

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.