Danny (1997) is a slow-moving, category one hurricane that made landfall on the coast of Louisiana and Alabama on 18-19 July 1997. It produced extreme amount of precipitation over Southern Alabama. Radar rainfall estimate for storm total precipitation was 43 in near Dauphin Island (Pasch 1997). Due to the slow-movement of the storm, Danny’s center remained within 100 km of WSR-88D radars at Slidell and Mobile for more than 48 hours. Radar observation of Danny has shown interesting structural evolutions at times near its landfall. This includes the development of concentric eyewalls, a complete eyewall replacement cycle, and the development of a convective mesoscale vortex in the western eyewall (Blackwell 2000). Because of nearly continuous radar observations for an extended period this case provides a unique opportunity for a detailed mesoscale verification of high-resolution model simulation of a hurricane at landfall.

In this paper, we performed a high-resolution numerical simulation of Danny over a four-day period, from its genesis stage to its landfall. The simulation began at 0000 UTC 16 July 1997 when only a weak surface low was present over northern Gulf of Mexico. The PSU/NCAR MM5 model with triply-nested (81/27/9 km) grids was able to successfully simulate the development of a small tropical cyclone 72 h into the simulation, and its subsequent landfall over the Gulf coast. Subsequent numerical experiments at 3 km and 1 km grid resolution successfully captured mesoscale structures of the storm, including the concentric eyewall, the eyewall replacement cycle, and the trochoidal oscillations in storm track, as observed by the ground-based Doppler radars. Additional numerical experiments with 3-km and 1-km MM5 indicated that the simulation of the genesis of Danny was very sensitive to the choice of precipitation physics and planetary boundary parameterizations, and the initial condition. Comparison of model simulated storm structure with radar observations of Danny will be presented at the conference. We will also discuss the physical processes responsible for the genesis of Danny.