Polarimetric signatures of severe convective storms in Lake Victoria: from waterspouts to downbursts in the tropics!

Abstract

<p>Lake Victoria is the largest freshwater lake in Africa, supporting the livelihood of more than 5 million people subsisting on its prosperous fishing industry and agriculture. However, the lake’s surrounding complex topography and geographic location makes this one of the deadliest regions of the world when it comes to weather-related accidents. It is estimated that more than 1,000 fishermen die yearly due to high waves produced by severe convective wind phenomena. Furthermore, severe hailstorms and flood-producing heavy rain events have increased in recent years in the extended East Africa (EA) regions, unfortunately also reporting several fatalities. </p> <p>In 2017, the World Meteorological Organization (WMO) launched the 3-year “High impact weather lake System” (HIGHWAY) project, with the main objective to reduce the loss of lives and goods in the lake basin and to improve resilience for the local communities. The project included a field campaign in 2019 to provide forecasters with high-resolution observations and to study the storm life cycle on the lake basin, with the utilization of S- and C-band dual-polarization radars in the surrounding countries. In this study, we use the high spatiotemporal resolution radar data from the field campaign in 2019 to investigate severe convection over the lake. We analyze two severe storms affecting the south and north shores of the lake (Tanzania and Uganda, respectively), identifying polarimetric signatures indicating severe weather, and testing the current capabilities of the radars’ scanning strategies. The results presented here are part of the ongoing high impact weather forecasting trainings and advancement efforts for East African countries towards the WMO Early Warning and Early Action 2025 goal, with a joint effort between WMO-led international projects, the National Center for Atmospheric Research, international non-profit organizations, and the National Meteorological and Hydrological Services in EA countries.</p>