Hook-Shaped Features in Hurricane Inner Core Region by Vertical Wind Shear and Dry Intrusion

With finer grid resolution and improved representation of hurricane dynamics and physics, regional numerical weather prediction models are beginning to be able to capture convective-scale features and fine structures in the inner cores of hurricanes. Recently, operational Hurricane Weather Research and Forecasting (HWRF) model forecasts have been observed to produce hook-shaped contours in pressure and geopotential height fields in hurricane inner core regions, which are usually associated with rapid weakening (or intensity oscillation), dry intrusion, and strong vertical wind shear (VWS). Hereafter, these features are referred to as hurricane hooks. Similar albeit weaker features have also been identified in other regional hurricane prediction models, and evidence from satellite and aircraft reconnaissance observations suggests the existence in nature of features similar to the hurricane hooks described here. Detailed analyses and diagnoses show that these hurricane hook features from the HWRF model forecasts correspond to a local warm anomaly generated by strong downdrafts, which are related to the dry intrusion, strong environmental VWS, and compensational subsidence associated with deep convection in the eyewall and rain bands. Improved understanding of the hurricane hooks and the associated dynamical and physical processes could benefit hurricane intensity forecasting and motivate improved approaches to determine storm intensity from observations and numerical models.