Asymmetric distribution of convection associated with tropical cyclones making landfall along the south China coast

This study investigates the asymmetric distribution of convection associated with tropical cyclones making landfall along the south China coast using Geostationary Meteorological Satellite 5 (GMS-5) data and Doppler radar data. Four tropical cyclones (TCs; Maggie, Sam, York, and Cam) that made direct landfall over Hong Kong in 1999, are chosen as case studies to examine the changes in the distribution of convection prior to, during, and after landfall. Based on the radar data, three of the four cases (Maggie, Sam, and York) generally showed enhanced convection to the western side of the TC center starting from ∼6 to 18 h before landfall, especially in the cases of Sam and York. For Cam, a dry continental air intrusion apparently destroyed much of the western and southern portion of its eyewall. From the satellite data, convection was generally more enhanced on the southward side. In other words, enhanced convection occurred to the west of the TC in the mid- to lower troposphere and was then advected to the southward side of the upper troposphere by the cyclonic flow and rising motion. These observations are consistent with previous observational and numerical studies. The possible influences of storm motion and vertical wind shear on the observed convective asymmetries are also examined for the cases of Sam and York. Both storms showed similar evolution of convective distribution relative to storm motion as they approached the coastline. Such storm-motion-related convective distributions may partly explain the observed convective asymmetries. The environmental vertical wind shear may be another factor contributing to the large left-right convective asymmetry in the case of Sam. © 2004 American Meteorological Society.