Despite significant impacts of heavy rainfall that often accompanies tropical cyclone landfall, quantitative precipitation forecasting (QPF) remains a challenge. Freshwater flooding associated with landfalling tropical cyclones has been responsible for more than half of all the deaths related to tropical cyclones in the United States over the last 30 years. Rainfall measured at a particular location during the passage of a tropical cyclone depends on many factors: location with respect to the storm's track, the maximum intensity and storm-relative distribution of rainfall, storm translational speed, and local effects such as topography and orientation of the coast. Consequently, precipitation can vary greatly from storm to storm and even over time during the same storm.

In this study the impact of vertical shear in determining the storm-relative distribution of total accumulated rainfall in high-resolution numerical simulations of tropical cyclones is investigated. The model used is the Penn State/NCAR mesoscale model MM5, with a minimum grid length of 1.67 km. Recent investigations of model-produced rainfall patterns in Hurricane Bonnie (1998) have shown that total rainfall is closely tied to the relationship between the magnitude and direction of the vertical shear experienced by the storm's inner core and the direction of the storm's forward motion. This relationship, as well as possible relationships to storm translational speed, will be further explored in simulations of Hurricanes Georges (1998) and Floyd (1999). These three storms experienced a variety of shear environments, storm motions, and topography. These different conditions will provide a broad range of environments with which to test the ideas governing the impact of vertical shear on the distribution of total rainfall with these simulated cyclones. When possible, comparisons will be made with ground-based radar and rain gage data to validate the rainfall forecasts.