Eddy Vorticity Fluxes in Rapidly Intensifying and Non-Intensifying Storms

Forecasts from the operational Hurricane Weather Research and Forecasting (HWRF) based ensemble prediction system for Hurricane Edouard (2014) were analyzed to study the differences in both the tropical cyclone inner-core structure and large-scale environment between rapidly intensifying (RI) and non-intensifying (NI) ensemble members. An analysis of the inner-core structure reveals that as deep convection wraps around from the downshear side of the storm to the upshear-left quadrant for RI members, vortex tilt and asymmetry reduce rapidly and RI occurs. For NI members, deep convection stays trapped in the downshear/downshear-right quandrant, and storms do not intensify. The budget calculation of tangential wind tendency reveals that the positive radial eddy vorticity flux for RI members contributes significantly to spinning up the tangential wind in the middle and upper levels and reduces vortex tilt. The negative eddy vorticity flux for NI members spins down the tangential wind in the middle and upper levels and does not help the vortex become vertically aligned. This difference suggests that positive radial eddy vorticity flux is a key process that contributes to intensity change in a sheared environment by spinning up the tangential winds in the middle-to-upper levels and reducing tilt. In this study, we will identify the large scale environment that sets up the configuration favorable for producing positive eddy vorticity flux at middle-and-upper levels.