Predictability of cyclones associated with heavy precipitation events in the Sahara

Abstract. Heavy precipitation events (HPEs) are a precious source of water in the Sahara, but often trigger devastating flooding. These events are strongly associated with surface cyclones, making accurate cyclone forecasting crucial for predicting hazards related to HPEs and their impacts. In this study, we investigate the predictability of HPE-associated cyclones across the Sahara and its drivers. We use ERA5 reanalysis and ECMWF initialized reforecasts between December 2000 and November 2020. Forecast skill on short-, medium-, and extended-range timescales is evaluated based on the overlapping areas of observed and forecasted cyclones over the Sahara. Results show that the lead time of skillful prediction is up to about 10 days. In winter, when cyclones are mainly located in the northern Sahara, forecast skill is higher for deeper cyclones. In summer, skill is higher for cyclones located in the southwestern Sahara. On short-range lead times, forecast skill is higher in winter, whereas on medium to extended lead times, skill is higher in summer and fall. Rossby wave patterns extending over the North Atlantic are associated with both high and low skill forecasts, highlighting a flow-dependent control on predictability over the Sahara and underscoring the need for more detailed investigation. These findings identify key controls and characteristics of skillful forecasts of cyclones that lead to HPEs in the Sahara on timescales of a few days to two weeks in advance. Understanding these variations across regions and seasons is key to improving the predictability of HPEs and their related impacts.