Thermodynamics of Convectively Induced Extreme Rainfall over the Guinea Coast of West Africa

Due to their rapidly changing atmospheric processes, forecasting thunderstorms from a merger of isolated cells is a complex task for highly-resolved numerical weather prediction models. This study employs a novel approach to identify mechanisms driving updrafts and downdrafts in thunderstorms that caused heavy rainfall and flooding in Kumasi and the Ashanti Region on June 23-24, 2021. Findings show that the moisture gradient between the south and north of the region deepens the planetary boundary layer through differential surface heating. Additionally, colder air aloft a warmer surface triggers atmospheric overturning, impacts CAPE and generates significant updrafts. Lower equivalent potential temperature before storms, combined with reduced warming, moisture, and increased mid-level vertical motions, promotes dry air entrainment, enhancing mid-tropospheric updrafts. Strong rainfall correlates with high soil moisture, evaporative fraction(EF), and variable CAPE and updrafts, sustaining surface convergence and upper-level divergence for prolonged convective activity. African Easterly Waves (AEWs) and low-level wind shear (LLWS) significantly influence updrafts and rainfall propagation. Furthermore, we found a single-cell thunderstorm with a variable wind pattern that impacted a defined path during the storm progression. These findings provide valuable information to enhance the development of early warning systems for detecting localized thunderstorm activities during the monsoon period.