Characteristics of African Easterly Waves in the SubX forecasting systems

The amounts of rainfall received during the single rainy season directly impact agricultural production and food security in the Sahel. Besides the seasonal totals, the distribution and intensity of rainfall within the season are also critical with prolonged dry spells affecting crops productivity and intense rainfall often leading to floods, crop and asset destruction and impacts on health and sanitation. The sub-seasonal forecasts, with multi-week lead-times, can provide much needed early warnings and increase preparedness to extreme events but their reliability over the Sahel has not been well documented yet. In this study, we take advantage of the CPO MAPP Test-bed project SubX providing 17 years of sub-seasonal re-forecast and two years of real-time forecasts from seven North American models. These re-forecasts and forecasts are issued once a week with up to four weeks lead time, following an inter-model consistent forecast protocol and are publicly available via the IRI Data Library. African Easterly Waves (AEWs) have been identified as a dominating mechanism of rainfall variability within the West African Monsoon on timescales of less than 10 days but their characteristics in the GCMs and relationship to model rainfall have often been found unsatisfactory. We will examine the main characteristics of the AEWs in the SubX model outputs, such as tracks, variability and relation to rainfall at different lead-times. We will also explore the potential for dynamico-statistical approaches to enhanced lead-time forecast of extreme events using predicted AEWs in support of a sub-seasonal forecasting system for Senegal.