Factors Influencing Extreme Precipitation Associated With Tropical Storm Fay (2008) Across North Florida and Southwest Georgia

On 24-25 August 2008, Tropical Storm Fay led to extreme precipitation across much of North Florida and Southwest Georgia. Despite the non-stationarity of the cyclone and its relatively weak intensity during the period in question, widespread rainfall in excess of 10" was observed across the region with maximum rainfall totals of 18-25" occurring in a narrow north-south corridor approximately 25 km east of Tallahassee, FL. These rainfall totals set or approached all-time daily and event-total precipitation records at many locations and the resultant runoff produced record mean and instantaneous maximum streamflows in multiple rivers across the region.

In this study, we attempt to quantify the meso-gamma to synoptic-scale processes influencing the extreme precipitation totals across North Florida and Southwest Georgia associated with Fay. Version 3.3 of the Advanced Research Weather Research and Forecasting (WRF-ARW) model is used to conduct a high-resolution (dx = 1.33 km) simulation of Fay centered on the domain and time period of interest. Multiple measures of model verification are obtained and presented to show that the model simulation accurately depicts the timing, location, and magnitude of the observed rainfall.

Analyses focus upon characterizing the synoptic-scale environment; detailing the structure and evolution of rain bands located upstream of Fay associated with much of the observed rains; and testing the hypothesis that frictional convergence in the apex of Apalachee Bay exerted a significant influence on the location of heaviest precipitation. To address this third point, simulations with modified coastline geometries are conducted and assessed to quantify the relative contribution of frictional convergence to the observed precipitation. Results from these analyses are synthesized to provide a comprehensive view of the multi-scale processes influencing the observed extreme rainfall associated with Fay.