Abstract
Lake Victoria in East Africa supports the livelihood of thousands of fishermen and it is estimated that 3000–5000 human deaths occur per year over the lake. It is hypothesized that most of these fatalities are due to localized, severe winds produced by intense thunderstorms over the lake during the rainy season and larger scale, intense winds over the lake during the dry season. The intense winds produce a rough state of the lake (big wave heights) that cause fishing boats to capsize. In this region, weather radars have never been a primary tool for monitoring and nowcasting high impact weather. The Tanzania Meteorological Agency operates an S-band polarimetric radar in Mwanza, Tanzania, along the south shore of Lake Victoria. This radar collects high temporal and spatial resolution data that is now being used to detect and monitor the formation of deep convection over the lake and improve scientific understanding of storm dynamics and intensification. Nocturnal thunderstorms and convection initiation over the lake are well observed by the Mwanza radar and are strongly forced by lake and land breezes and gust fronts. Unexpected is the detection of clear air echo to ranges ≥100 km over the lake that makes it possible to observe low-level winds, gust fronts, and other convergence lines near the surface of the lake. The frequent observation of extensive clear air and low-level convergence lines opens up the opportunity to nowcast strong winds, convection initiation, and subsequent thunderstorm development and incorporate this information into a regional early warning system proposed for Lake Victoria Basin (LVB). Two weather events are presented illustrating distinctly different nocturnal convection initiation over the lake that evolve into intense morning thunderstorms. The evolution of these severe weather events was possible because of the Mwanza radar observations; satellite imagery alone was insufficient to provide prediction of storm initiation, growth, movement, and decay.
Highlights
The purpose of this paper is to provide the first radar observations obtained over Lake Victoria in East Africa
In this study we have explored the contribution of S-Band dual polarization radar data for observation, evaluation, and movement of localized, large clusters of deep convection compared to traditional observation platforms that have existed in the region, including satellite observation
During the first storms propagated to the west coast of Tanzania with new storms being triggered along the leading edge of the storms by the low-level gust front
Summary
The purpose of this paper is to provide the first radar observations obtained over Lake Victoria in East Africa. These radar observations are important since they are from an area where deep intense thunderstorms are common, and they are responsible for the loss of many lives. The data shows clear-air features over the lake that has great potential for developing severe storm and wind warnings. This initial data has only been minimally integrated with other observations such as lightning, satellite, and surface station.
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