Potential vorticity and surface layer stability in hurricane movement: case studies of Hurricanes Harvey and Ida

It has been known that potential vorticity (PV) diagnostics can be employed to (a) evaluate large-scale dynamics of hurricane movement, and (b) assess the storm’s influence on its own track. Moreover, PV variations and temperature adjustments at the tropospheric interior and the associated general circulation theory are closely related to the surface PV. Diagnosis of the surface PV is, however, complicated due to data availability/coarse-resolution configurations across the wide terrain in topographic regions. In this work we develop a high-resolution configuration for the Gulf of Mexico (GoM) region for employing in the Weather Research and Forecasting (WRF) model to study Hurricanes Harvey and Ida. The new configuration includes horizontal resolutions of 5 km and 1.67 km in the main and nest domains, respectively; 55 vertical heights (potential pressure levels) are also considered. Forecasts of Hurricane Harvey for 132-hours (5days + 12 hrs), and Hurricane Ida for 78-hours (3days + 6 hrs) are performed, and outputs are stored at every 15 minutes. It is shown that surface PV changes its sign when the Hurricane Harvey/Ida arrives over the land while PV at high altitudes are conserved. We show that the surface PV change is due to the change of vertical temperature gradient at the surface (i.e. change of surface layer stability). These dynamical evolutions are coincident with an increase in precipitation rate and accumulated precipitation of hurricane aftermath. We discuss how these meteorological processes can possibly influence hurricane movements.