Barotropic vortex motion near large-scale mountain ranges: Case studies ofHurricane Gilbert (1988) and Tropical Storm Hermine (1980)

A shallow-water model is used to examine the motion of a barotropic vortex on an equatorial beta plane in the presence of a large-scale mountain range that represents the Sierra Madre of Mexico. The model is initialized with the analyzed large-scale winds of two Atlantic storms, Hurricane Gilbert (1 988) and Tropical Storm Hermine (1980). The study is focused on understandi ng the motion of tropical cyclones in the western Gulf of Mexico. Vortices representative of each storm are found to experience southward def lections as they approach the Sierra Madre. The deflections are attributed to the divergent production of relative vorticity associated with vortex st retching as fluid columns are advected over the mountains. While variations of the depth and stratification of the model atmosphere are also found to influence the track of the vortex, the presence of the mountains is shown t o produce the most dominant effect. Additional information on the motion of the vortex is also determined through an examination of the asymmetric pot ential vorticity held.