Although the rapid intensification of Katrina was noteworthy, the expansion of the tropical storm-force winds is the key forecast issue. The devastation wrought by this storm upon landfall is attributable more to its size rather than its intensity, as it landed as a Category 3 hurricane. This large hurricane caused a record storm surge and exposed Louisiana and Mississippi to hurricane-force winds for a long period of time.
The Hurricane Weather and Research Forecast system (HWRF) model will be used to explore the causes of this intensification and wind field expansion. HWRF is a coupled air-sea-land prediction system with a movable nested grid and physics suitable for high resolution.
Data assimilation will be conducted using a 3-h 3DVAR data assimilation cycling run. Sensitivity experiments will be performed using conventional observations, resonnaissance, satellite, and radar data. No bogussing will be used, as model initialization will be attempted using real inner-core wind data. Model coupling experiments will then be performed, with careful consideration of oceanic data in the loop current region, using the Model Coupling Environmental Library.
Once a successful simulation of the hurricane structure is completed, relative angular momentum (RAM) calculations will be performed to understand the cause of the wind field expansion. The methodology of Tuleya and Kurihara (1975) is to be followed, and the individual contributions by the following terms will be assessed: 1) mean flux convergence of RAM; 2) eddy flux convergence of RAM; 3) Coriolis contribution; 4) horizontal torque; and 5) vertical torque. The utilization of other cylindrical terms, broken up by quadrants, will also be done as necessary, such as done by McBride (1981).