Tropical Cyclone Landfall under the influence of Uniform Flow

This study investigates the changes in the structure of a tropical cyclone (TC) during landfall using the MM5 model version 3.7. Double-nested domains of 15-km and 5-km resolutions are used in the idealized numerical experiments. The spun-up vortex is steered towards the land surface by easterly flows of uniform strength 4, 6 or 8 m s-1 on an f plane.

In all experiments, a jet of maximum wind speed can be found in the rear quadrant of the vortex at the sigma level of 0.995, just prior to landfall. Such jet exists on the right-frontal quadrant at the sigma-level of 0.87 at the same time. At the time of landfall, there is an abrupt decrease in wind speed at the sigma-level of 0.995 at the onshore side, while the region of maximum wind prevails on that side at the sigma-level of 0.87. This indicates the existence of a region of high vertical shear between these two sigma levels on the onshore side during landfall.

As the vortex moves further inland, there is tendency for the region of maximum wind speed at the sigma-level of 0.995 to stay over the coastline, lagging behind the surface center of the vortex. More detailed results will be presented in the extended abstract and the conference.