<p>Despite relatively constant surface temperatures, seasonally-varying rainfall in the Lake Victoria Basin is approximately bimodal with maxima during the equinoctial seasons. Rainfall amounts are lower during boreal winter, and boreal summer is dry. Explanations of this seasonality involving movement of the intertropical convergence zone (ITCZ) are incorrect since the ITCZ, characterized by low-level meridional moisture convergence, is not identifiable over the Lake Victoria Basin. The ERA5 reanalysis is evaluated and used to understand the seasonality of Lake Victoria Basin precipitation, including the influence of land/lake mesoscale circulations and local topography. A consideration of diurnal time scales is included since averaging over the region’s pronounced diurnal cycles obscures physical processes. The unique features of the Lake Victoria Basin precipitation and the large-scale connections that determine its seasonality are evaluated. Seasonal variations in the continental-scale geopotential height field and the seasonal formation and breakdown of the Somali jet provide a large-scale framework for understanding the region’s seasonality. Interactions with mesoscale hydrodynamics associated with lake/land circulations and orographic flow superimpose to provide a more complete understanding.</p>