HURRICANE-INDUCED SURGE AND CURRENTS ON THE TEXAS-LOUISIANA SHELF

This study consists of numerical model simulations of hurricane-induced surge and currents on the Texas-Louisiana shelf. The numerical experiment includes the simulation of multiple hurricane tracks with landfalling points along the Texas-Louisiana coast. A parallel storm that traverses the entire Texas-Louisiana coastline is also modeled to assess the difference in shelf response between landfalling and parallel storms. The grid extends from the Texas-Mexico border to the Gulf Coast of Florida, with the ocean open boundary seaward of the shelf break. Along-shelf and cross-shelf surge and current variability are assessed as a function of shoreline geometry and bottom topography. A complementary one-dimensional mixed layer model is used to evaluate the vertical structure of the currents and the maximum depth of hurricane influence. The choice of landfalling storm tracks is based principally on historical storm tracks for the Texas-Louisiana area. Storm intensity, i.e., central pressure depression, for all storms is set equal to the 10-year recurrence interval central pressure. Strong cyclonic flow is induced by the hurricane wind field within a distance from the storm's center equal to 3 to 5 times the storm's radius of maximum winds. Far-field hurricane winds generate a northward moving coastal jet along the west coast of Florida, particularly for the landfalling storms. The far-field continental shelf currents are topographically steered by the shoreline and bathymetry. There is strong evidence of a cyclonic-anticyclonic eddy pair being generated in the wake of the parallel storm traveling eastward over the continental shelf. An intercomparison of the one-and two-dimensional models shows that for depths less than 50 m, the combined use of the surge and mixed layer models permits a description of the vertical and horizontal hurricane-induced current patterns. The surge height computations for a given storm strength point to the importance of several factors that determine surge levels as a function of offshore distance. These factors are bathymetry, topography, angle of approach of the storm, distance to landfall location, and shelf width. The most dramatic increase in surge levels occurs in depths less than 10 m, where the surge profile mirrors the changes in the bottom slope. In contrast, the sensitivity of surge dynamics to shelf width is neither strong nor consistent. A narrow spread of maximum surge values is observed. Each transect is examined individually to explain local behavior and the reason for the modest variation in surge values among dissimilar geographical areas. No critical dependence on the exact storm angle exists for storm angles within the range of angles associated with maximum surge generation (within 20-degrees counterclockwise from the shore-normal direction). Since the landfalling storms used in this study fall into this category, no significant dependence of surge height on the landfalling angle is observed.