Analyzing Tropical Cyclone Rain Shields According to Storm Size

Researchers have examined the spatial distribution of tropical cyclone (TC) rainfall by sectioning the rain shields of numerous storms with a circular grid. However, the use of a “one size fits all” grid does not account for variations in storm size. This study examines 11 U.S. landfalling TCs to determine if a relationship exists between storm size and the spatial extent of the rain shields. Base reflectivity radar returns are entered into a GIS and interpolated into polygon shapes to define the spatial extent of the rain shield. Three circular grids are used to divide the rain shields into sections, and the percentage of each grid section containing a portion of the rain shield is calculated. The first grid, used to section all rain shields, consists of annular rings spaced in 55 km increments. The spacing of the second and third grids is unique to each TC as they are based on one half of the mean radius of 27.5 m/s and 17.5 m/s winds. Hurricane rain shields are also sectioned using a grid based on the mean radius of 32.9 m/s winds. Results of the study suggest that hurricane rain shields generally extend out to a radius that is 1.5 times the mean radius of 17.5 m/s winds. Less intense TCs that have asymmetrical circulations due to the influences of physical forcing mechanisms such as wind shear have a relatively small size, causing rain shields to extend outward six to seven times the mean radius of 17.5 m/s winds. These findings suggests that it may be appropriate to consider storm size and well as asymmetries present in the storm circulation when investigating TC rainfall distributions.