The Evolution of Rainfall and Convection in Rapidly Intensifying Tropical Cyclones based on 16 years of TRMM Data

Using 16 years of observations from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI), rainfall and convection distributions in tropical cyclones (TCs) are examined with respect to the evolution of rapid intensification (RI) events. The onset of RI follows a significant increase in the areal coverage of total rainfall (rain rate > 0.5 and 1 mm/hr), cyan of 37 GHz color composites, and shallow precipitation (defined as 85 GHz polarization corrected brightness temperature (PCT85) between 260 K and 275 K) upshear-left, which in turn could be used as potential parameters to predict RI. Storms during RI periods (RI onset to 24 hours before RI ends) are featured with increased total rainfall and moderate precipitation (200 K < PCT85 ≤ 260 K). This increase concentrates in the upshear semicircle, especially upshear-right, in the early stage of RI and rotates cyclonically, concentrating to the right of shear in the middle of RI. Very deep convection (PCT85 ≤ 160 K) is most frequent upshear-left 12-24 hours before the RI onset but rapidly decreases in the follow 24 hours, with a percent occurrence < 1% during RI. The beginning of RI ending period (a 24-h period before RI ends) is related to a significant decrease in the total rainfall and cyan coverage. The magnitude of vortex vertical misalignment is quantified using the Automated Rotational Center Hurricane Eye Retrieval (ARCHER). The tilt of vortex is large prior to, and near the onset of RI, but decreases quickly in the middle of RI events, indicating that the vertical alignment is a result rather than a trigger of RI.