Effects of mountainous terrain on hurricane boundary layer winds

Significant improvements in forecasting tropical systems have been made over the years by the development of more intricate, detailed numerical models. This study looks at the possibility of a simple, dry hurricane model being able to accurately predict hurricane winds over land. A strong emphasis has been placed on storm track and intensity forecast in past models, but the model being used in this study specifically looks at the boundary layer wind structure of a hurricane over mountainous terrain. The results of this model could help isolate the most extreme wind events over these areas resulting in increased readiness before the storm and faster damage control after.

Several terrain features were used with the model to see the effects they produced on low-level windflow. Flat land, a circular mountain, an elongated mountain, and land data of the island of Taiwan were all used in this study. Changes in surface roughness, terrain height and size, and landfalling positions were all examined to see the effects on the wind profiles. Several features such as a lee-side flow and higher wind speeds over the mountain ridges were similar to other modeling studies using more advanced models.

The increased resolution seen with this model showed higher detail in the wind vector patterns, especially over mountain peaks. This detail is further enhanced by using lower horizontal diffusion values and shows small features produced by the mountains that are not seen in other studies. Comparisons between the northern Taiwan landfalling experiment and the work of Wu et al. (1999), using the MM5 model to simulate typhoon Herb show these small features that are missed in the MM5 output. The highly resolved features seen in the wind pattern suggests that this model is more than sufficient for modeling boundary layer winds over mountainous terrain.