The time varying fields of surface winds, sea state and currents associated with Hurricane Ivan (2004) in the Northern Gulf of Mexico are specified through the implementation and application of advanced numerical wind, wave and ocean hindcast models, all adapted to the entire Gulf of Mexico at higher resolution than used in previous simulations of tropical cyclones in this basin. An extensive validation of the wind and wave hindcast indicates that the storm response is specified with 10% or better accuracy. No public domain current measurements were available in Ivan to validate the current model results but validation of the same modeling technology against the extensive currents measurements in previous Gulf of Mexico hurricanes suggests that the spatial and vertical structure of the primary current speed response to Ivan are reasonably well simulated.
The objective of this study is to develop a comprehensive, definitive and reliable database of wind, sea state and currents associated with Hurricane Ivan (2004) in the Northern Gulf of Mexico (GOM), through the implementation and application of advanced numerical wave and current hindcast models. The database is not only of intrinsic value, but also a critical element of investigations of the considerable impact of Ivan on GOM offshore operations and infrastructure. In this sense the study and objectives are analogous to those of our previous comprehensive studies of Hurricanes Andrew (1,2) and Lili (3). Like these past studies this hindcast builds upon methods that have continuously evolved over the past 35 years to measure, describe, understand and model the surface marine meteorological characteristics of GOM hurricanes and the corresponding ocean response to their passage (4,5,6,7). This methodology has been applied in major joint industry programs to hindcast all hurricanes affecting the Gulf of Mexico since 1900 and to develop reliable extreme event metocean design data (8,9,10).
Many of the hurricanes hindcast in government and industry-sponsored studies cited above have included high quality wind, wave, water level and ocean current measurements (Audrey, 1957; Bertha, 1957; Carla, 1961; Camille, 1969; Edith, 1971; Delia, 1973; Frederic, 1979; Danny, 1985; Juan 1985, Andrew, 1992, Georges, 1998, Lili, 1992). These validation studies (e.g.11, 12) demonstrated the accuracy of our hindcast methods when applied to specify peak sea states (significant wave height) at an arbitrary site in a Gulf of Mexico hurricane (bias of less than 0.5 m, mean absolute error of less than 1.0 m and scatter index of 10-15%). The inner core of Ivan passed over NOAA data buoy 42040 and other nearby buoys experienced severe winds and sea states thereby providing measurements of the profile of surface winds and sea state across the storm that are invaluable in the validation of the hindcast reported here.
The ocean current model used is the state-of-art Hybrid Coordinate Ocean Model (HYCOM) (13) which has already been proven to be superior to other models for the combined modeling of the deep ocean and the continental shelf, providing a consistent bridging between these dynamically very different regimes.
