Numerical Simulation of Typhoon Gladys (1994) and Its Interaction with Taiwan Terrain Using the GFDL Hurricane Model

Numerical integrations using the Geophysical Fluid Dynamics Laboratory (GFDL) hurricane model were performed to study the evolution of Typhoon Gladys (1994) and its interaction with the Taiwan terrain. Consistent with most previous studies, the Taiwan topography results in the deceleration of Gladys’s translation speed and southward deviation as it approaches Taiwan. On the other hand, Gladys accelerates northwestward while passing Taiwan, which is likely to be related to the moist processes, and differs from the track pattern in the dry model of Lin et al. Although the GFDL hurricane model forecast underestimates Gladys’s intensity, the model can capture the evolution of Gladys’s intensity, especially its weakening during landfall, which is primarily due to the cutoff of the water vapor supply in the boundary layer as Gladys approached the Taiwan terrain. Other mesoscale phenomena, including the pattern of heavy precipitation and the formation of secondary lows, are well simulated by the model, though their locations are somewhat different from those observed. Detailed analyses indicate that the surface low pressure center to the east of the Central Mountain Range (CMR) is induced by the downslope adiabatic warming (foehn) associated with the circulation of Gladys. The quasi-stationary secondary low to the west of the CMR is mainly induced by the environmental easterly flow over the CMR, while the downslope adiabatic warming associated with the circulation of Gladys acts to enhance it as Gladys is close to Taiwan. The potential vorticity budget analysis indicates that the condensational heating plays a major role in the potential vorticity evolution around the storm, while the surface frictional dissipation of the potential vorticity becomes more significant as Gladys is over the Taiwan terrain. Finally, the experiment with a larger and stronger initial typhoon vortex indicates that different initial specification of a typhoon vortex can result in a different track pattern and thus leads to a totally different typhoon–topography interaction, suggesting the importance of typhoon initialization for storm prediction near Taiwan.