Forecast Forum - July 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.  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 the observed oceanic and atmospheric patterns and recent trends, it is likely that warm-episode (El Ni�o) conditions will develop during the next 3 months.

Discussion

Sea surface temperature anomalies increased substantially in the central equatorial Pacific (Ni�o 3.4 region) during July 2004, while anomalies greater than +0.5�C persisted in the Ni�o 4 region (Table T2). 

Positive SST anomalies greater than +1�C were found between 180�W and 140�W, while negative SST anomalies less than -0.5�C were found between 120�W and the South American coast (Fig. T18). By the end of July, positive SST anomalies greater than +1�C extended from 180�W eastward to 125�W. The recent increase and eastward expansion of positive SST anomalies in the central equatorial Pacific indicate the possible early stages of a warm episode. In spite of the anomalous warmth in the central equatorial Pacific during July, there appears to be little or no reflection of that warmth in the pattern of deep convection (precipitation) (Figs. T25, E3) or in the pattern of low-level winds (Fig. T20) over the region.

Considerable intraseasonal variability (MJO activity) in recent months has resulted in week-to-week and month-to-month variability in many atmospheric and oceanic indices (Table T1). During mid-June through early July the easterlies weakened in many areas of the equatorial Pacific (Fig. T13), as enhanced convection shifted eastward from the Indian Ocean to the western tropical Pacific (Figs. T11, T12). By mid-July the low-level winds and equatorial convection returned to near average in many areas of the equatorial Pacific. However, a strong oceanic Kelvin wave, initiated by the weaker-than-average easterly winds in June, has propagated eastward resulting in a substantial deepening of the oceanic thermocline (Figs. T15 and T16) and an increase in the subsurface temperature anomalies in the central and east-central equatorial Pacific (Fig. T17). This Kelvin wave is expected to reach the South American coast during August.

Given the recent trends and observed oceanic and atmospheric patterns discussed above, there is about a 50% chance that the NOAA operational definition for El Ni�o [Oceanic Ni�o Index (ONI), a three-month running mean of the Ni�o 3.4 index, greater than or equal to +0.5�C] will be satisfied for the period June-August 2004. It seems most likely that SST anomalies in the Ni�o 3.4 region will remain positive, at or above +0.5�C, through the end of 2004. At this time it is not clear what, if any, impacts this event will have on ocean temperatures in the classical El Ni�o region (Ni�o 1+2) along the west coast of South America.

Approximately half 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) through the end of 2004 (Figs. F1, F2, F3, F4a, , F4b, F5, F6, F7, F8, F9, F10, F11, F12, F13) The remaining forecasts indicate El Ni�o conditions (Ni�o 3.4 SST anomalies greater than or equal to +0.5�C) will develop within the next 3-6 months.

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.