An Examination of Local Shear, Vortex Tilt, and Tropical Cyclone Intensity Change Using Airborne Radar Observations

Tropical cyclone (TC) intensification involves a multi-scale interaction of convective- and vortex-scale processes with the synoptic-scale environment. Previous work has demonstrated one of the primary environmental influences on TC intensity change is the vertical wind shear. Although these previous studies have documented multiple pathways through which vertical shear can limit or prevent TC intensification, often times the magnitude of the vertical wind shear that the TC “feels” can be challenging to quantify. In some instances, the TC is able to locally modify the larger-scale environmental flow through convectively-driven diabatic processes, resulting in a local-shear magnitude that may be appreciably smaller than the large-scale shear magnitude.

Through the utilization of airborne radar observations, this study explores the three-dimensional structure of the vertical wind shear and its relationship to both TC vortex tilt and intensity change. This is achieved through a climatological analysis of over 20 different TCs occurring between 1997–2018 in the eastern North Pacific and North Atlantic basins sampled by NOAA’s WP-3D aircraft. Here, we will compare local shear estimates to shear magnitudes computed using winds within larger domains, such as those currently used in operational statistical TC intensity models. The relationship between TC vortex tilt and the vertical shear computed within multiple different domains will be assessed. The shear profiles, and the associated vortex tilt configurations, associated with TC intensification will be compared to those associated with TCs of steady-state intensity. It is hypothesized the local shear magnitude is a stronger predictor of TC intensity change than shear estimates derived using the background synoptic-scale flow.