One of the most significant human impacts associated with tropical cyclones is property damage caused by high winds speeds as the storm makes landfall. If the coastline is adjacent to high orography, as is the case along the eastern coast of the island of Taiwan, then forecasting the potential for high wind speeds becomes a much more difficult problem. During the Tropical Cyclone Structure – 2008 (TCS-08) experiment, two typhoons made landfall on Taiwan: Sinlaku and Jangmi. Surface stations along the coast documents both strong westerly winds flowing down the slopes of the mountains, as well as more moderate southerly flow when wake effects predominated. Numerical simulations using a version of the Naval Research Laboratory's Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®) designed for tropical cyclones (COAMPS-TC) does an excellent job of reproducing this observed wind field.

To further understand the dynamics controlling the presence of downslope versus coastally channeled flow, a series of idealized simulations were performed using a Rankine vortex and an elliptical, sinusoidal island. In the absence of terrain or a mean flow, the idealized tropical cyclone was found to maintain symmetry indefinitely. When a homogenous mean flow was added, the movement of the storm stayed close to this steering in both the cross-track and along-track direction. The interaction of the vortex with the island produced many of the same features seen in observations and the real-data simulations. To evaluate the sensitivities of these features, the size and intensity of the storm was varied, as well as the location of its landfall and the strength and vertical structure of the steering flow. The results of these experiments will be summarized in this presentation.