Structure and Evolution of Developing and Non-developing African Easterly Waves during NAMMA

A modeling and data impact study using the HWRF model was performed to explore the mechanisms by which some African easterly waves (AEWs) develop into tropical cyclones and others fail to intensify. Two AEWs from the 2006 hurricane season were examined. One AEW is the precursor of Hurricane Helene (HAEW). The second AEW preceded the Helene AEW, but failed to intensify into a tropical cyclone. The Hurricane EnKF Data Assimilation System was utilized to assimilate HWRF dropwindsonde data collected during the NAMMA campaign, which was not ingested into NOAA/NCEP numerical models in real time. East-west zonal vertical cross sections of moisture, winds, shear, and vorticity have been created for HWRF model output of runs in which dropwindsonde data were and were not assimilated in order to evaluate the dynamic-thermodynamic vertical structure and environment evolution of the AEWs. Results from the runs without data assimilation suggest that moisture availability in the AEW immediate environment and the formation of a strong consolidated vortex aligned with the wave axis is essential for development. However, other favorable conditions in a horizontal and vertical scale must persist in order for tropical cyclogenesis to occur. It is expected that by assimilating dropwindsonde data into HWRF, triggers of tropical cyclogenesis can be confirmed, and improvements in the track and intensity predictions of the HAEW can be achieved.