From March to May 2024, East Africa (EA) experienced several heavy rainfall events, resulting in flooding, loss of life, destruction of infrastructure and crops, and loss of livestock and wildlife. However, the underlying causes of this unprecedented heavy rainfall remain unexplored. This study investigated the anomalous atmospheric circulation associated with these extreme rainfall events, utilizing daily observations of rainfall, atmospheric reanalysis, and sea surface temperatures. Here, the study shows that the heavy rainfall events were driven by the Madden-Julian Oscillation (MJO) and Tropical Cyclone (TC) Hidaya over the southwest Indian Ocean (SWIO). In early/late March, the presence of the MJO-related westerly/easterly wind anomaly over the Congo Basin/western Indian Ocean, brought warm air temperature into EA, resulting in moisture convergence and a positive rainfall anomaly. In early and late April, MJO-related northeasterly/westerly wind anomaly from the western Indian Ocean/Congo Basin transported warm air toward EA, leading to moisture convergence and wet conditions. In early May, extreme rainfall resulted from both the MJO and TC Hidaya. These systems led to anomalous westerly and easterly winds that brought warm air and moisture convergence over EA. Despite the MJO being active in late May, the Mascarene high shifted westward and strengthened, steering a cool southerly wind anomaly that caused dry conditions in EA in two ways: first, by blocking MJO-related moist westerly winds anomaly from the Congo Basin, and second, by triggering frictionally induced subsidence along the coastal region. This knowledge of the interplay between the extreme rainfall, the MJO, TC activity, and the Mascarene high movement can help local weather forecasters enhance the accuracy of sub-seasonal predictions.
Laban Lameck Kebacho (Tue,) studied this question.