Quantification of Shear-relative Precipitation Asymmetries of Tropical Cyclones in Different Intensity Change Stages and during the Evolution of Rapid Intensification Using 16 years of TRMM Data

In this study, the precipitation asymmetry of Tropical Cyclones (TCs) is quantified by the Fourier decomposed perturbation normalized by the azimuthal mean rain rate from the 16–yr Tropical Rainfall Measuring Mission (TRMM) Mircowave Imager (TMI) 2A12 rain rate estimates. The dataset of 2,107 TMI overpasses of global TCs including tropical storms through category 2 hurricanes is categorized by the future 24–h intensity change into rapidly intensifying (RI), slowly intensifying, neutral, and weakening stages. For the subset of 595 overpasses associated with RI events, it is classified into before RI, during RI, and RI ending categories. The TMI 2A12 rain rate is categorized into four precipitation types including total precipitation (rain rate greater than 0.5 mm hr^-1), light precipitation (rain rate between 0.5 and 5 mm hr^-1), moderate precipitation (rain rate between 5 and 10 mm hr^-1), and heavy precipitation (rain rate greater than 10 mm hr^-1). Distributions of the shear–relative precipitation asymmetry are examined for different intensity change stages and during the evolution of RI events. The distribution of normalized wavenumber 1–6 asymmetries indicates that all four types of precipitation of non–RI storms are more asymmetric than RI storms. For the RI event-based analysis, the normalized wavenumber 1–6 asymmetries in the inner core region of all four types of precipitation decrease 3 to 9 hours before RI onset. Especially, the frequency of light precipitation increases in the upshear quadrants and gradually wraps around the storm center after the onset of RI. This type of decrease in rainfall asymmetry could be used as a predictor of RI.