Validation of MM5 and WRF Forecasts of the Development of Hurricane Helene

Each year, about 50 African Easterly Waves (AEWs) move off the West African coast and traverse the tropical Atlantic. Of these 50 AEWs, ten to fifteen may develop into tropical storms and half of that number into hurricanes. With an increase in the number and intensity of tropical cyclones (TCs) in the Atlantic over the past few years, questions have arisen on the effects of the Saharan Air Layer (SAL) and its interaction with tropical cyclogenesis. It is known that when TCs interact with the SAL they have a hard time sustaining development due to a decrease in moisture content dryness and overabundance of cloud condensation nuclei (CCN). When TCs move away from the SAL, rapid intensification has been noted. Numerical simulations using both MM5 and WRF along with NAMMA data are being conducted to better understand the interaction of AEWs with the SAL. For these simulations to be useful, a measure of the simulation accuracy is needed. Multiple simulations using different cumulus, boundary layer, and microphysics parameterization schemes were conducted to identify the parameterization schemes necessary to adequately model the development of the TCs off western Africa. Hurricane Helene was chosen for these simulations because of the wealth of data collected during the NAMMA field campaign in 2006. The goal is to simulate the evolution of Helene from an AEW into a tropical storm and then into hurricane as accurately as possible. These simulations will then be used to explore the effects of the SAL on Helene in hopes of gaining a better understanding of this intricate interaction.