Mesoscale Circulation and Intensity Changes of a Landfalling Typhoon: Role of the Coastal Barrier Jet

Abstract

Abstract Using coastal radar and surface observations of Taiwan, an investigation of intensity and structure variations in the inner core of Typhoon Haitang (0505) is conducted. Within a 3-h period (1933–2233 UTC 17 July 2005), Haitang experienced intensity vacillation with merging of the eyewall with a rainband induced by the coastal barrier jet (CBJ); concentric eyewall breakdown and weakening; and eyewall recovery, contraction, and re-intensification. The northerly flow of the CBJ converged with the southerly flow of a leeside meso-low to form a west–east line of convection south of the storm when the storm was still 100 km offshore. The rainband propagated radially inward and triggered eyewall–rainband interaction. The interaction resulted in approximately 30% amplification of precipitation and 20% decrease in the axisymmetric tangential wind. Barotropic instability is speculated to be the underlying dynamic process. The recovery of the eyewall, following nearshore eyewall axisymmetrization and contraction, resulted in a 40% intensity increase before landfall. Significance Statement The behaviors and underlying physical processes of a landfalling tropical cyclone (TC) under the influence of complex terrain are studied by using coastal radars. The TC inner core structure and intensity change, including concentric eyewall breakdown, weakening, eyewall recovery, eyewall contraction, and re-intensification that occurred 3 h before TC made landfall are documented. The terrain-induced coastal barrier jet and leeside meso-low helped to form an intense line convection near the southern fringe of the eyewall and triggered the rainband–eyewall interaction.