Processes associated with tropical cyclone landfall along the South China coast

Abstract

This study investigates the landfalling processes of tropical cyclones (TCs) with focus on the South China coast. From analyses of best track data in this area for nearly 40 years, it is found that on the average, a landfalling TC would first deflect to the right then to the left starting some 12 hours before landfall, and also experience an increase in drifting speed at landfall time. When decomposing the TC motion into "landward and "coastward" components, it appears that the increase in drifting speed is mainly contributed by an increase in landward speed, and the directional deflections are related to fluctuations in coastward speed. Four case studies, apart from one exception with dry air intrusion, show that convection is stronger to the left of a landfalling TC. Also local terrain is found to be conducive to the formation of convection activites. There is also evidence suggesting that the overall convection does not die off quickly soon after landfall possibily due to the increase of moisture influx brought by the increased frictional inflow. Through the concept of potential vorticity tendency (PVT), it is concluded that zonal asymmetries in diabatic heating would direct a TC southwards. Vertical heating profile is also important in the sense that diabatic heating concentrated in the upper (lower) troposphere would induce the TC to move towards (away from) that heating area.