Rainfall, Convection, and Latent Heating Distributions in Rapidly Intensifying Tropical Cyclones

Abstract

ropical cyclone (TC) rainfall, convection, and latent heating distributions are compiled from 14 years of Tropical Rainfall Measuring Mission (TRMM) precipitation radar overpasses. The dataset of 818 Northern Hemisphere tropical storms through category 2 hurricanes is divided by future 24-h intensity change and exclusively includes storms with at least moderately favorable environmental conditions. The rapidly intensifying (RI) category is further subdivided into an initial [RI (initial)] and continuing [RI (continuing)] category based on whether the storm is near the beginning of an RI event or has already been undergoing RI for 12 or more hours prior to the TRMM overpass. TCs in each intensity change category are combined into composite diagrams orientated relative to the environmental vertical wind shear direction. Rainfall frequency, defined as the shear-relative occurrence of PR near-surface reflectivity >20 dBZ, is most strongly correlated with future intensity change. The rainfall frequency is also higher in RI (continuing) TCs than RI (initial). Moderate-to-deep convection and latent heating only increase significantly after RI is underway for at least 12 h in the innermost 50 km relative to the TC center. The additional precipitation in rapidly intensifying TCs is composed primarily of a mixture of weak convective and stratiform rain, especially in the upshear quadrants. The rainfall frequency and latent heating distributions are more symmetric near the onset of RI and continue to become more symmetric as RI continues and the rainfall coverage expands upshear. The relationship between rainfall distributions and future TC intensity highlights the potential of 37-GHz satellite imagery to improve real-time intensity forecasting.