Observed Concentric Eyewalls of Supertyphoon Hinnamnor (2022)

Abstract

Ground-based radar observations of the concentric eyewalls (CEs) of supertyphoon Hinnamnor (2022) showed that CEs evolved as follows: (Stage 0) development of a distinct stationary band complex (SBC) downshear in moderate south-southeastward vertical wind shear (VWS), (Stage 1) maturity of the secondary eyewall (SE), (Stage 2) contraction of the SE, and (Stage 3) decay of the CE structures. From Stage 0 to Stage 1, the SBCs transitioned into an axisymmetric SE, and moats appeared a few hours after SE formation. Outer rainbands formed successively in the down-to-left shear quadrants and developed wide stratiform regions with a vast anvil cloud extending outward as they moved upshear. When the anvil cloud covered the right-shear quadrants, the stratiform regions started contracting. Evolutions of the doppler velocity fields were detected under the anvil and stratiform regions of each rainband. An intense convection developed at the inner edge of the contracting SE as regions with relatively high doppler-velocity merged. When the core region was surrounded by multiple well-developed rainbands, the inner eyewall weakened rapidly. The radar observations revealed the importance of moderate-to-weak VWS and development of a SE as a rainband complex during evolution of CEs.