Evolution of Precipitation in Easterly Wave Critical Layers during Tropical Cylogenesis as Observed in TRMM Data

Data from the Tropical Rainfall Measurement Mission (TRMM) Microwave Imager (TMI) are used to examine the spatial and temporal evolution of precipitation during the tropical cyclogenesis stage for tropical cyclones over the Atlantic and East Pacific basins. Recent work has demonstrated that the Kelvin cat's eye circulation within the critical layer of an easterly wave is the preferred location for tropical cyclogenesis. Initial results from TMI composite rain rate analyses centered on this location, moving westward with the parent wave, show that convection is favored in the Kelvin cat's eye circulation as genesis nears. Precipitation within the critical layer is disorganized spatially and temporally from 72-48 hours prior to genesis. Within 24 hours of genesis, areal coverage and intensity of convection increases rapidly. There is a rapid increase in the number of convectively-dominated heavy precipitation pixels within the entirety of the critical layer immediately preceding genesis. This suggests the presence of a convectively divergent heating profile, conditions that are favorable for "bottom-up" type development. Asymmetries the in highest rain rates are observed within 24 hours of genesis, with precipitation maxima to the northwest and southeast of the critical layer center. To further support these findings, data from the TRMM Precipitation Radar (PR) is presented. The TRMM PR offers direct retrievals of latent heating profiles and a superior algorithm for stratiform versus convective partitioning. Data from the TRMM PR allows validation of the spatial and temporal pattern observed in the TMI observations and provides additional details on the evolution of precipitation in developing easterly waves.