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 conditions and the SST predictions, weak-to-moderate warm episode (El Ni�o)conditions are expected to continue during the remainder of 2002 and into early 2003.

Discussion

Warm episode (El Ni�o) conditions prevailed in the tropical Pacific during July 2002. Sea surface temperature (SST) anomalies remained greater than +1�C throughout the central equatorial Pacific between 170�E and 130�W (Fig. T18). For the second consecutive month the Ni�o 3, Ni�o 3.4 and Ni�o 4 indices were all at or above +0.5�C (Table T2). Atmospheric indicators of a warm episode (El Ni�o) include consistently negative values of the Southern Oscillation Index (SOI) since March 2002 (Table T1), and weaker-than-average low-level easterly winds during May-July 2002 throughout the equatorial Pacific (Fig. T7).

The Madden-Julian Oscillation (MJO) continues to be a major source of week-to-week and month-to-month variability in the atmospheric circulation of the Tropics and subtropics (Figs. T11, T12, T13). The MJO contributed to a substantial weakening of the low-level easterly winds throughout the equatorial Pacific during July (Figs. T13, T20). As a consequence, drier-than-average conditions were observed over Indonesia and portions of Southeast Asia / India during the month (Figs. T25, E3, E4). In addition, the weaker-than-average easterly winds contributed to a deepening of the oceanic thermocline in the central equatorial Pacific (Figs. T15, T16), an increase in subsurface temperature anomalies (Fig. T17) and an increase in SST anomalies in the central equatorial Pacific (Fig. T9).

The oceanic and atmospheric variables discussed above reflect the presence of weak-to-moderate El Ni�o conditions. This assessment is consistent with most coupled model and statistical model forecasts (Figs. F1, F2, F3, F4, F5, F6, F7, F8, F9, F10), which indicate that El Ni�o conditions are likely to continue through the end of 2002 and into early 2003. While SST anomalies in several of the models decrease in the first season and then remain above average in subsequent seasons (e.g. Figs. F2 and F4), those in other models increase in the first season (e.g. Figs. F6 and F10). Since each model has its own initialization, this may be related to month-to-month variations in initial conditions due to the strong MJO activity noted above. Although there is considerable uncertainty in the forecasts about the timing and intensity of the peak of this warm episode, all of the forecasts indicate that it will be much weaker than the 1997-98 El Ni�o. It is important to add that the global impacts of this warm episode should be correspondingly weaker than those observed during the very strong 1997-98 El Ni�o.

Based on the current conditions in the tropical Pacific, on the SST predictions, and on results from historical studies of the effects of ENSO, we expect drier-than-average conditions to continue over Indonesia and eastern Australia during the next several months, and wetter-than-average conditions over southeastern South America during the next three months. In the United States drier-than-average conditions are expected in the Pacific Northwest and mid-Atlantic states during the fall and early winter and in the Ohio Valley states during the winter. Wetter-than-average conditions are expected in the Gulf Coast states during the winter, and warmer-than-average conditions are expected in the Northern Great Plains, upper Midwest, and western and central Canada during late fall and winter.