Factors Leading to Extreme Precipitation on Dominica from Tropical Storm Erika (2015)

Tropical Storm Erika was a weak tropical storm in a sheared environment that passed through the Lesser Antilles on August 27th of 2015. Radar and rain gauges measured at least a half meter of rainfall on the Commonwealth of Dominica in about five hours. This unexpected heavy rainfall caused substantial loss of life and property in Dominica, exposing prediction challenges and devastating power of tropical cyclone-induced rainfall. Understanding the factors leading to heavy rainfall for this case is important for future prediction of similar weak, sheared, tropical storms passing near mountainous islands.

In this study, we use a combination of several observational datasets, from both ground- and aircraft-based platforms. Observations show that the combination of a sheared environment, a dry northern sector, and a mesovortex contributed to the significant storm precipitation. The sheared environment (especially below 500 hPa) affected the storm, causing it to weaken, but also organized the heaviest precipitation in the region that passed over Dominica. A mesovortex embedded within the sheared-organized convection moved over Dominica and persisted for several hours, thus enhancing rainfall totals. These results highlight the multi-scale interactions that can contribute to heavy precipitation associated with tropical cyclone passage near mountainous islands.