SS: Metocean: Comprehensive Hindcast of Hurricane Ike (2008) in the Gulf of Mexico

Abstract

ABSTRACT The immense impact of Hurricane Ike (2008) on Gulf of Mexico (GOM) offshore infrastructure and production is unexpected for a Saffir-Simpson Scale (SSS) Category 2 hurricane. This paper describes a comprehensive hindcast of the surface wind and sea state fields generated by Ike that shows that the extreme ocean response is mainly caused by a marked expansion of the wind circulation after the eye of the storm crossed the western tip of Cuba, leading to storm with a large radius of maximum wind speed and a shelf-like radial wind speed profile. The modeling of these attributes required the description of the radial pressure distribution in the boundary layer in terms of a double exponential analytical formulation. The fitting of that functional form utilized all conventional meteorological data, high-temporal density flight level measurements made by reconnaissance aircraft and remotely sensed satellite meteorological data within an analyst-assisted workstation that allows the fitting of either the classical single exponential form or, if appropriate, the more complex form. The surface wind field is specified by solutions of a newly recalibrated primitive equation mesoscale boundary layer model augmented by available kinematic analyses of the inner-core wind structure derived directly from measured wind data. The wave response is hindcast by a proven third generation (3-G) spectral wave model adapted to GOM at high resolution that includes shallow water effects and incorporates a saturation surface wind drag formulation consistent with recent hurricane inner core measurements of same. The hindcast and available measurements support that Ike generated peak significant wave heights of about 45 feet (~14 m) in the north central GOM. The hindcast is compared to public-domain wave measurements currently available and good skill is evident. In the near term these results aid post-mortem engineering studies conducted to ascertain causes and modes of failure of damaged platforms and other infrastructure and to assess the suitability of related designs. Of longer term significance, the hindcast methodology applied to Ike has been used to incorporate the impact of lower ranked SSS hurricanes and of all hurricanes that exhibit the non-classical radial pressure and wind structure on the specification of extreme metocean criteria derived either by the direct historical or deductive approaches.