Variations in Tropical Cyclone Size and Rainfall Patterns Based on Synoptic-Scale Moisture Environments in the North Atlantic

Abstract

Prior research has shown that tropical cyclone (TC) size, which is integral in determining the spatial extent of TC impacts, is influenced by environmental wind shear and the overall moisture environment. This study considers North Atlantic TCs located within low to moderate wind shear and at least 100 km from major landmasses. An empirical orthogonal function (EOF) analysis is applied to distinguish moisture environments based on the spatial pattern of total column water vapor surrounding the TC. Using these EOF patterns, four separate categories (groups) are created. Principal component scores indicate the TC samples most contributing to each EOF pattern and ultimately determine the cases in each group. TC structural differences among the groups are compared using size metrics based on the wind and precipitation fields and shape metrics based on the precipitation field. These metrics are considered across a 48-hr window centered on the sample times evaluated in the EOF analysis. There are no statistically significant differences in the TC wind field size, but TCs with abundant moisture to the southeast have larger rain areas with more outer rainbands. TCs in a dry environment or with dry air southeast of the TC center have generally smaller rain areas and less closed rainbands than TCs with moisture to the southeast. Future work will investigate the physical processes contributing to these spatial differences in precipitation.