Intensification of Hurricane Sandy (2012) through Extratropical Warm Core Seclusion
The modeling results show that intensification occurred in response to shallow low-level convergence below 850 hPa that was consistent with the Sawyer-Eliassen solution for the secondary circulation that accompanied the increased baroclinicity in the radial direction. Additionally, cyclonic vertical vorticity generated by tilting of horizontal vorticity along an axis of frontogenesis northwest of Sandy was axisymmetrized. The axis of frontogenesis was anchored to the Gulf Stream in a region of near-surface differential diabatic heating. The unusual northwestward track of Sandy allowed the cyclonic vorticity over the Gulf Stream to form ahead of the main vortex and be readily axisymmetrized. The underlying dynamics driving intensification were non-tropical in origin, and supported the reclassification of Sandy as extratropical prior to landfall.