A Simple Diagnostic for Eyewall Replacement in Tropical Cyclones Based on Wind-Pressure Relationship

Secondary eyewalls occur in 70% of major tropical cyclones, and are associated with rapid changes in storm intensity and rapid broadening of strong winds. In this study, we present to use the radial gradient of absolute angular momentum with Holland's wind model as a simple diagnostic for eyewall replacement induced by boundary layer imbalance. The diagnostic is solely dependent on the maximum wind speed, the radius of maximum wind, and the latitude and shown to compare well with global satellite observations of concentric eyewall from 1991-2020. The diagnostic can be expressed as a latitude-irrelevant Rossby Number of primary eyewall, varying with the peakedness of wind. It provides a valuable tool to improve the understanding, modeling and risk assessment of storms with eyewall replacements.