Forecast Forum - January 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

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

Discussion

Sea surface temperatures remained warmer than average in the central and western equatorial Pacific and near average in the eastern equatorial Pacific during January (Figs T9, T18). Equatorial ocean surface temperatures greater than +0.5°C (~1°F) above average were found between Indonesia and 165°W, and departures greater than +1°C were found between 160°E and 175°W (Fig. T18). Positive SST anomalies decreased in all of the Niño regions from December to January (Table T2).

At the moment there are no discernable impacts from the anomalously warm waters on the atmospheric circulation. The monthly 850-hPa zonal wind indices, OLR index, 200-hPa zonal wind index, SOI and EQSOI have not shown any significant trends over the last few months that would support a transition to either El Niño or La Niña (Table T1, Fig. T2). However, many of these indices have exhibited considerable week-to-week variability since late November in response to tropical intraseasonal (Madden-Julian Oscillation) activity. Wetter-than-average conditions, observed over the tropical Indian Ocean in late November, shifted eastward to the western Pacific by late December and into the central Pacific by early January (Fig. T11). As the convective activity shifted eastward, the equatorial easterlies weakened over the western and central Pacific (Fig. T13) and westerlies developed near the date line (180°W). During the last half of January the equatorial easterlies intensified, becoming stronger than average over the central and western equatorial Pacific, as the convectively inactive phase of the MJO shifted eastward over the region (Fig. T13).

The weakening of the equatorial easterlies in late December - early January initiated an eastward propagating oceanic Kelvin wave, which is evident in the recent evolution of upper ocean temperature anomalies (Figs. T15, T17). More recent observations from the TAO buoy array indicate that this Kelvin wave is propagating eastward at about 8-10 degrees of longitude per week. At that rate, the Kelvin wave is expected to reach the vicinity of the west coast of South America around the end of February. NOAA’s Climate Prediction Center (CPC) will continue to monitor this situation to determine what, if any, impacts the Kelvin wave will have on surface and subsurface temperatures along the South American coast.

A majority of the statistical and coupled model forecasts indicate near-average conditions in the equatorial Pacific (Niño 3.4 SST anomalies between -0.5°C and +0.5°C) through the early Northern Hemisphere spring 2004 (Figs. F1, F2, F3, F4a, F4b, F5, F6, F7, F8, F9, F10, F11, F12, F13). Thereafter, the forecasts show increasing spread and greater uncertainty. The three-month (November-January) average SST anomaly in the Niño 3.4 region (+0.5°C) is at the threshold (+0.5°C) required for NOAA to declare a weak Pacific warm episode (El Niño). However, the SST indices all decreased slightly during January 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 through the Northern Hemisphere early spring 2004.

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.