Concentric Eye Walls, Secondary Wind Maxima, and The Evolution of the Hurricane vortex

Research aircraft observations in recent hurricanes support the model of Shapiro and Willoughby (1982) for the tropical cyclone's response to circularly symmetric, convective heat sources (convective rings). In both nature and the numerical model the tangential wind commonly increases rapidly just inside the radius of maximum wind and decreases inside the eye near the central axis of the vortex. Thus both secondary outer wind maxima and eyewall wind maxima often contract as they intensify. This response is independent of the horizontal spatial scale of the maximum. An outer maximum is frequently observed to constrict about a pre-existing eye and replace it. This chain of events often coincides with a weakening, or at least a pause in intensification, of the vortex as a whole. The concentric eye phenomenon is a common, but by no means universal, feature of tropical cyclones. It is most frequently observed in intense, highly symmetric systems.