A look at Tropical Storm Gaston flooding in Virginia

Gaston was a weakening tropical depression as it moved into Virginia on 30 August 2004. It had produced a swath of 2 to 4 inch rainfall before sunrise 30 August 2004 in North Carolina, and all model forecasts showed continued weakening as Gaston continued to move northeast through Virginia. Instead, Gaston increased in intensity and became a tropical storm again, once it moved off the Maryland coast. This intensification helped to substantially increase the rainfall in Virginia. Gaston produced record flooding across central Virginia with numerous rainfall reports of 4 to 8 inches and reports even as high as 12 inches. A 500 year rainfall event occurred in Richmond, VA with several deaths resulting from the flooding.

This paper will examine how the environment changed as the storm moved into Virginia and how this contributed to the increase in rainfall. The use of observational data, surface and upper air observations and satellite, will be examined to determine how the environment was changing. Various model forecasts will be compared to this observational data to demonstrate how model data needed to be adjusted to fit the observed data. Based on this comparison, implications for the future forecast will be presented. Also, the model forecast and observational data will be used to explain why the heavy rain and accompanying record flooding focused over central Virginia.