Radar Observations of Inner Rainband Contributions to Eyewall Formation During the Rapid Intensification of Typhoon Cempaka (2021)

Abstract This study utilizes coastal radar observations to investigate eyewall formation processes during Typhoon Cempaka's (2021) rapid intensification. Two distinct types of inner rainband governed the evolution of eyewall formation: (a) strain‐generated bands forming inside the radius of maximum winds (RMW) through cellular convection, and (b) vortex Rossby wave‐coupled bands developing outside the RMW via convergence‐driven convection. When strain‐generated bands dominated near the RMW, a mean tangential wind tendency budget indicates that enhanced convection inside the RMW contributed to net spin‐up at lower levels, promoting RMW contraction. Meanwhile, the prevalence of wave‐coupled bands beyond the RMW led to significant wind acceleration near and outside the RMW, primarily driven by symmetric contributions. The axisymmetrization of these inner rainbands ultimately resulted in eyewall formation. These radar‐based findings underscore the critical role of inner rainbands in eyewall formation, contrasting with previous studies that emphasize outer rainbands.