Potential Vorticity Structure and Evolution of Hurricane Patricia (2015)

While much progress has been made in understanding tropical cyclone (TC) intensity change, skillful forecasts are still a difficult challenge. Operational numerical models failed to forecast the record-setting rapid intensification and rapid over-water weakening of Hurricane Patricia (2015), producing some of the highest forecast errors in recent years. In an effort to better understand the mesoscale processes involved in TC intensity change, analysis of research aircraft observations from Hurricane Patricia on 22 - 23 October has been conducted. The field observations include in situ data, Doppler radar, and full-tropospheric dropsonde profiles of temperature, humidity, and winds that were collected as part of the Office of Naval Research Tropical Cyclone Intensity (TCI) field experiment and NOAA Intensity Forecasting Experiment (IFEX). Spline-based variational analyses of these observations allow for calculation of axisymmetric potential vorticity (PV) at high resolution throughout the troposphere during the rapid intensification and weakening period. The analyses reveal the formation of a “hollow tower” PV structure as Patricia rapidly approached its peak intensity, consistent with previous theoretical and modeling studies. Patricia’s rapid weakening phase corresponded to a breakdown of this structure, and suggest a rearrangement of the PV in a manner consistent with mixing at the eye-eyewall interface. Further insights into Patricia’s structural and intensity changes are obtained by viewing the PV in isentropic and potential radius coordinates. The research presented will summarize the observed PV structure and evolution and discuss the potential factors that led to rapid intensification and weakening.