Forecast Forum - December 2004

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.  Niño 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

Warm-episode (El Niño) conditions are expected to continue for the next three months.

Discussion

Positive sea surface temperature (SST) anomalies greater than +0.5°C (~1°F) persisted  across most of the central and western equatorial Pacific during December 2004 (Table T2, Fig. T18).  Positive equatorial SST anomalies greater than +1°C (~2°F) were found from 160°E eastward to 155°W (Fig. T18).  During December SST anomalies exceeded 0.5°C in the Niño 4, Niño 3.4 and Niño 3 regions, while anomalies remained near zero along the West Coast of South America (Niño 1+2 region) (Table T2). The pattern of anomalous warmth in the equatorial Pacific in recent months (Fig. T9) and the most recent 5-month running mean values of the Southern Oscillation Index (Fig. T1) indicate that a weak warm (mid-Pacific El Niño) episode has developed. However, through December 2004 there has been a lack of  persistent enhanced convection over the anomalously warm waters of the central equatorial Pacific (Figs. T8 and T25), which has limited El Niño-related impacts on the global pattern of precipitation.

Since late 2003 tropical intraseasonal (Madden-Julian Oscillation) activity has resulted in week-to-week and month-to-month variability in many atmospheric and oceanic indices (Tables  T1 and T2).  In the past few months the warmth in the central equatorial Pacific has supported eastward shifts of enhanced convection associated with the convectively active phase of the MJO across the western equatorial Pacific (Figs. T11 and T12).  The MJO activity weakened considerably during early November 2004 and remained weak through mid-December.  However, during the last half of December the MJO strengthened, as enhanced convection and precipitation over the Indian Ocean shifted eastward across Indonesia .  By early January 2005, enhanced convection extended into the western tropical Pacific. The Climate Prediction Center will continue to closely monitor the evolution of this activity over the next several weeks as it shifts eastward over the abnormally warm waters in the central equatorial 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 2004 is +0.9°C, which satisfies the NOAA operational definition of El Niño for the fifth consecutive month. Based on the recent evolution of oceanic and atmospheric conditions and on a majority of the statistical and coupled model forecasts (Figs. F1, F2, F3, F4a, F4b, F5, F6, F7, F8, F9, F10, F11, F12 and F13), it seems most likely that warm (mid-Pacific El Niño) episode conditions will persist for at least the next three months. However, there is considerable uncertainty concerning future developments in the extreme eastern equatorial Pacific (the classical El Niño region).

Expected global impacts include drier-than-average conditions over portions of Indonesia (through early 2005), northern and northeastern Australia (through February 2005), and southeastern Africa (through March 2005). If the warming in the tropical Pacific strengthens and spreads eastward to the South American coast, then wetter-than-average conditions would be expected in coastal sections of Ecuador and northern Peru during March-April 2005, and drier-than-average conditions would be expected to develop in Northeast Brazil during February through April 2005. Expected US impacts during Northern Hemisphere winter include warmer-than-average conditions in the West and in the northern Plains, and cooler- and wetter-than-average conditions for portions of the South and Southeast. (Note: The recent pattern of heavy precipitation in California during December 2004 and early January 2005 was associated with 1) persistent high-latitude blocking in the vicinity of the Gulf of Alaska and an associated trough along the West Coast, and 2) a weaker than average jetstream across the central and eastern Pacific. These circulation features are not consistent with El Niño, which would favor a stronger-than-average jetstream over the central and eastern Pacific and  a reduced tendency for blocking in the Gulf of Alaska ).

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.