Review of seasonal forecasting techniques and their applicability to Southern Africa

The development of a seasonal rainfall forecasting capability has recently become a priority of many research organisations in Southern Africa, but the methodologies used are still at an early stage of development. In other areas, high forecast skills are generally associated with tropical atmospheric variability, largely because of a thermally direct response of the tropical atmosphere to oceanic heat anomalies. Over South Africa, most current forecast skill relates to rainfall variability attributable to the tropical atmospheric circulation, including El Nino-Southern Oscillation (ENSO)-related anomalies. Consequently, highest forecastability exists in the summer rainfall region during the peak rainfall months, December to February, and is particularly high in areas that are strongly affected by ENSO activity. The extratropical atmosphere has an important influence on the rainfall of the region during the first half of the summer season, when forecast skill is relatively low. Occasionally, the extratropical atmosphere also remains dominant 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 blocking should result in considerably improved skill for seasonal forecasts throughout the summer season.