A numerical simulation associated with Typhoon Dot (1990) was made using the fifth-generation Pennsylvania State University - National Center for Atmospheric Research Mososcale Model (MM5) initialized with data from the Tropical Cyclone Motion (TCM-90) field experiment. The physical processes which occurred during the discontinuous track of Typhoon Dot over Taiwan are investigated.

Observational and numerical results show that a region of low pressure developed over the central part of western Taiwan, induced primarily by strong adiabatic warming on the leeside of the Central Mountain Range (CMR) associated with the downslope easterly winds of the typhoon. A few hours later, a dominant leeside secondary vortex formed via a vortex stretching process over southwestern Taiwan with the original low-level vortex of Dot being blocked and weakened, and gradually dissipating on the eastern side of the CMR. The region of low pressure was larger than the final stretched induced secondary vortex. During the dominant secondary vortex formation, a leeside low-pressure center shifted southwestward and merged with a low-level vorticity center over the southwestern coast of Taiwan. Simulation results also indicate that the mid-level vortex of Dot passed over Taiwan with a continuous track, and then interacted with the dominant secondary vortex over southwestern Taiwan. Finally, the midlevel and secondary vortices coupled vertically and appeared to reestablish Typhoon Dot’s contiguous vertical structure as it continued its northwest journey.