Hurricane Gabrielle (2001) formed a few hundred miles from the Florida coast only three days before making landfall. This project simulated the formation of Gabrielle using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research mesoscale model (MM5). The simulation results, along with available observations, were examined for the large-scale and mesoscale factors that influenced Gabrielleís transition from a cold-core non-tropical disturbance to a warm-core tropical cyclone. This project found that asymmetric rainfall created circulation anomalies that, when axisymmetrized, provided the energy to fuel the transition of the disturbance to the warm-core Gabrielle. This asymmetric rainfall was organized by vertical wind shear interacting with the disturbance. This systemís reliance on vertical wind shear for development significantly differs from previous research on tropical cyclone formation, which stresses low vertical wind shear.