The Mid-level Contribution of Hurricane Rafael to the Genesis of Hurricane Sandy

The contributions of Hurricane Rafael to the genesis of Hurricane Sandy, especially in terms of mid-level vorticity, are examined using cloud-resolving WRF simulations. As Rafael moved north of Puerto Rico between 15 and 17 October, a region of mid-level vorticity separated from a dangling trough axis on the southeast side of Rafael, remaining nearly stationary over the northeastern Lesser Antilles. Starting on 18 October, the vorticity moved southwest until early the following day when it was located over the pre-Sandy system, then a weak and convectively-inactive easterly wave. Over the next 48 hours the wave became more convectively active and genesis occurred 18 UTC 21 October.

The goal of this research is to test the hypothesis that a mid-level vorticity feature from Rafael had a significant impact on the evolution of the pre-Sandy disturbance by transforming the system from a weak easterly wave devoid of convection to a viable tropical convective system. Cloud resolving WRF model simulations, with ECMWF operational analysis initial conditions, will be used to assess the impact of this mid-level vorticity feature on the development of the pre-Sandy disturbance. Potential vorticity inversion will be used to remove the vorticity feature from the initial conditions and the evolution of the pre-Sandy disturbance after this vortex removal will be compared to a control run with unmodified initial conditions.