Island‐Induced Eyewall Replacement in a Landfalling Tropical Cyclone: A Model Study of Super Typhoon Mangkhut (2018)

Abstract

AbstractAn unconventional, island‐induced eyewall replacement (IER) occurred in Super Typhoon Mangkhut (2018) when it crossed Luzon Island. Upon landfall, its original compact eyewall broke down and dissipated rapidly. As Mangkhut exited Luzon and entered the South China Sea, a much larger new eyewall formed at a radius of 150–200 km from the storm center, three times larger than the original one. Unlike the eyewall replacement cycle in intense tropical cyclones, the breakdown of the original eyewall preceded the formation of the new eyewall (NEF) in Mangkhut. This evolution was reproduced reasonably well in a control experiment using the Weather Research and Forecasting Model. Two sensitivity experiments showed that the IER was triggered by Luzon Island, whose terrain is essential for not only the destruction of the original eyewall but also the NEF. In an axisymmetric framework, it is demonstrated for the first time that the NEF was preceded by the following processes: (a) an increase in the outward‐directed agradient force in the boundary layer (BL) inflow region after landfall due to differential rates of weakening between the radial pressure gradient and the tangential wind, (b) creation of a BL deceleration zone, (c) localized reinforcement of BL inflow deceleration within the NEF region when Mangkhut re‐entered the ocean, following an exisiting framework of an unbalanced dynamical pathway, and (d) strengthening of the BL convergence and uplift which initiated and sustained the deep convection of the new eyewall.