Hindcast of Winds, Waves and Currents in Northern Gulf of Mexico in Hurricanes Katrina (2005) and Rita (2005)

Abstract

Abstract The evolution of the response to Hurricanes Katrina and Rita of sea state, ocean currents and water level in the northern Gulf of Mexico (GOM) is prescribed through the application of advanced numerical ocean response hindcast models. The wave hindcast utilizes a third-generation model that had been extensively validated against recent severe GOM hurricanes. For the present study a high resolution nested grid system (3 nm grid spacing basin-wide; 0.6 nm spacing in the coastal zone) is implemented. Currents and storm surge in shallow water are modeled with the ADCIRC community hydrodynamic model and mixed layer currents in deep water are modeled with a newly calibrated turbulence-closure current profile model. The wind fields in these hurricanes and especially in Katrina during the 24-hours before landfall, exhibited anomalous features that precluded the use of a simple wind modeling approach. Therefore, the wind fields used to drive the ocean response models were kinematically reanalyzed from all available in-situ, airborne and satellite data sources. The ocean response hindcasts were validated against all available measurements and generally exhibited good skill and negligible bias except at NOAA buoy 42040, which reported the highest significant wave height (16.9m), where the hindcast is about 10% lower than the measurement. These hindcasts were made to support the MMS sponsored program on post-mortem engineering studies; they are also of needed for the reassessment of design criteria. Introduction The purpose of this study is to develop a comprehensive, validated and reliable database of wind, sea state, and currents (vertically averaged in shallow water, mixed layer profile in deep water) associated with Hurricanes Katrina (2005) and Rita (2005) in the Northern Gulf of Mexico (GOM) through the implementation and application of advanced hindcast models. This study is necessary because virtually no measurements of surface winds and ocean response were acquired at the locations of offshore industry platforms, drilling units and pipelines affected by the storm. Reliable estimates of peak conditions experienced at such locations are needed for engineering studies of failure modes as well as for the reassessment of design criteria. The models adopted have been previously applied and validated against historical GOM hurricanes and are also validated against the scant measured data acquired offshore in these two hurricanes at the locations of NOAA moored data buoys. This study is analogous to comprehensive studies that we have performed of Hurricane Andrew (1992) carried out in 1993-1994 (1), Hurricane Lili (2) and Hurricane Ivan (3). The hindcast database is intended to satisfy the needs for wind, wave and current data for participants of the MMS (Minerals Management Service) program launched to assess the impact of Katrina and Rita on the offshore infrastructure. The hindcast methodology applied in this study 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, and 7).