A geospatial analysis of radar reflectivity data from landfalling tropical cyclones

It is important to determine where a tropical cyclone (TC) will produce high rainfall rates during landfall so that regions prone to flooding can be identified. This study employs a GIS to quantify the spatial attributes of heavy rainfall regions located within TCs through an analysis of radar reflectivity returns. The spatial analysis is performed for areas within the TC having reflectivity values of 40 dBZ or higher during a 24 hour period following 43 TC landfalls in the United States. The GIS is utilized to calculate the radial and azimuthal positions of the centroids of the heavy rainfall regions, as well as the areal extent of these regions. These attributes are then related to five factors: a) storm intensity, b) vertical wind shear, c) storm motion, d) whether or not the tropical cyclone becomes extratropical, and e) the distance between the storm circulation center and its heavy rainfall regions and the nearest point on the coastline. As forward velocity increases in conjunction with an extratropical transition, the heavy rainfall regions move outwards from the circulation center, shift from the right side to the front of the TC, and grow in size. A similar radial shift but with a decrease in areal extent occurs as TCs weaken. The heavy rainfall regions shift clockwise as vertical wind shear increases, but a statistically significant relationship between shear and the radial position or areal extent of heavy rainfall is not observed. To more effectively link the location of heavy rainfall to environmental variables, future work will utilize the GIS to quantify the shape and orientation of the rainfall regions. Adding these spatial attributes to the size and location data presented in the current study will allow a complete set of spatial attributes to be cataloged for each region of heavy rainfall.