REVIEW OF SEASONAL FORECASTING TECHNIQUES AND THEIR APPLICABILITY TO SOUTHERN AFRICA

The development of a seasonal rainfall forecasting capability has rece ntly become a priority of many research organisations in Southern Afri ca, but the methodologies used are still at an early stage of developm ent In other areas, high forecast skills are generally associated with tropical atmospheric variability, largely because of a thermally dire ct response of the tropical atmosphere to oceanic heat anomalies. Over South Africa, most current forecast skill relates to rainfall variabi lity attributable to the tropical atmospheric circulation, including E l Nino-Southern Oscillation (ENSO)-related anomalies. Consequently, hi ghest forecastability exists in the summer rainfall region during the peak rainfall months, December to February, and is particularly high i n areas that are strongly affected by ENSO activity. The extratropical atmosphere has an important influence on the rainfall of the region d uring the first half of the summer season, when forecast skill is rela tively low. Occasionally, the extratropical atmosphere also remains do minant during the peak summer months, resulting in a poor forecast for that season. Consequently, an improved understanding of the response of the temperate atmosphere to tropical anomalies and internal blockin g should result in considerably improved skill for seasonal forecasts throughout the summer season.