Understanding the environmental conditions of the extreme precipitation event on June 20, 2015, in the city of Douala, Cameroon

Abstract

Understanding the atmospheric conditions that trigger extreme precipitation events is paramount for advancing weather forecasting. For this purpose, the present study aims diagnosing the physical and synoptic processes that underpinned the June 20, 2015, extreme rainfall event in the city of Douala, using ERA5 reanalysis datasets. The results reveal the occurrence of stronger mass convergence (5.0 × 10-4Kg.m-1s-1) on June 20 compared to the days before (2.24 × 10-4Kg.m-1s-1, June 19) and after (2.85 × 10-4Kg.m-1s-1, June 21). This convergence originated from the eastern equatorial Atlantic Ocean. This process initiated during the night at 0000 UTC and progressively intensified, reaching its peak (21.59 Kg.m-1s-1) at 0900 UTC corresponding to the peak of precipitation (4.4 mm/hour). Afterwards, it gradually decreased from 1200 UTC to 2100 UTC. In response to the increased moisture availability, atmospheric instability was enhanced due to a strengthening of latent static energy, which led to an increase in moist static energy. This resulted in anomalously strong and deep convection on June 20 compared to June 19 and 21. The present work demonstrates that analyzing moisture and energy budgets can assist forecasters in nowcasting such extreme precipitation events over southern Cameroon with a high level of accuracy.