The impact of wind circulation on the incidence and nature of rainstorms over Dar es Salaam, Tanzania

Using storm rainfall data from a dense network of autographic raingauges at Dar es Salaam, Tanzania, storm characteristics (morphology, alignment and time of occurrence) are related to prevailing gradient wind. There is a pronounced seasonal variation in the time of day at which storms generally occur, related to seasonal changes in the larger‐scale wind regime between the north‐easterly and south‐easterly trade winds. Many storms occur at times when there is a convergence between locally‐generated land‐ or sea‐breezes and the gradient wind, and their origin along these lines of convergence is further demonstrated by occurrence of both elliptical and linear morphology storms aligned along the coast. The trend of the coast is shown to control the alignment of storms, particularly by day, whereas by night gradient wind is more important. At this time, storms tend to form along the direction of the gradient wind. The most active storms form in the middle of the day, are linear in nature, aligned parallel to the coast, and occur when the gradient wind is either offshore or blows along the coast from the south‐south‐east.