A Metric for Rainfall Asymmetry in Recurving Tropical Cyclones

Using a data set of 138 recurving tropical cyclones (TCs) from 2004 to 2015 in the western North Pacific, a new metric, B_rain, is proposed, which quantifies the asymmetry in the rainfall within the TC circulation relative to its track. When B_rain is positive (negative), the rainfall has a right of track (left of track) preference. Using the new metric, the rainfall asymmetry is found to be closely related to thermal structure asymmetry (B) in TCs. A well-defined anticorrelated relationship is found between B_rain and B for all recurving TCs. Prior to recurvature, B_rain decreases linearly as B increases. After recurvature, the linear relationship weakens, and TC rainfall is almost entirely concentrated left of track as B increases. A phase-space composed of B_rain and B provides substantial insight into cyclone structural and rainfall asymmetric evolution.