Outer Vortex Wind Structure Changes During and Following Tropical Cyclone Secondary Eyewall Formation

ABSTRACT: Some recent studies have utilized flight-level (700 mb) winds to document the maximum wind speeds (Vmax) and radius of Vmax (Rmax) of the original and secondary eyewalls during 24 Atlantic hurricane eyewall replacement cycles (ERC). In this study, Hurricane Wind (H*Wind) analyses of Atlantic hurricanes during 2003-2005 are utilized to document changes in the outer vortex surface wind profile beyond the secondary eyewall, with a focus on the radii of gale-force winds (R34) that are often defined operationally as size changes. In Mode 1, complete and partial ERCs in which the pre-, during-, and post-ERC outer wind profiles have approximately the same shape, the outward displacements of Rmax leads to size (R34) increases as much as 100 km. Mode 2 ERCs are characterized by sharpened wind profiles outside the secondary eyewall that offset the larger Rmax radii to produce only small R34 increases. While statistically significant results are not obtained, the differences in size changes for Mode 1 and Mode 2 SEF cases suggest practical significance for forecasts and warnings. Keywords: tropical cyclone structure, tropical cyclone size changes, secondary eyewall formation