Search for: All records

Abstract This study explores how a wind‐dependent surface drag coefficient (C_D) influences secondary eyewall formation in tropical cyclones (TCs), using Super Typhoon Gaemi (2024) as a case study. We employ the Weather Research and Forecasting model with two different C_Dparameterizations and find that changing C_Dmarkedly affects boundary‐layer convergence and outer rainband evolution. In particular, the latest C_Dscheme with larger surface drag coefficient at wind speeds less than 45 m s⁻¹yields higher surface stress and stronger boundary‐layer convergence in the outer core, thereby enhancing rainband convection and triggering earlier formation of a more coherent secondary eyewall structure compared to the scheme with smaller, nearly constant C_Dat wind speeds greater than 45 m s⁻¹. These findings underscore the fundamental role of surface friction in shaping TC structure, with direct implications for operational TC forecasting, especially during eyewall replacement cycles.