The emphasis of this study attempts to examine the residue-free budgets of vorticity and surface pressure to delineate the motion of the center of Atlantic Hurricanes. We particularly are interested in the governing fluid-dynamic and physical properties that create 'Recurving' Hurricanes as they track westward across the Atlantic Basin. Using the T126 Florida State Global Spectral Model with Physical Initialization (FSUGSM hereafter) and the ECMWF analyses for several Atlantic Hurricanes (1998: Bonnie, Danielle; 1999: Cindy, Gert), we perform a 'with and with' experiment calculating, separately, the time tendencies for the dynamical and physical components contributing to each storm's recurvature.

We propose to answer the question: What steering mechanism contributes most strongly to the recurvature of a Tropical Cyclone - the large-scale non-linear dynamics or the storm's internal physics. Here the steering mechanisms, although being isolated, coexist with the rest of the physics of the model.

To answer the above inquiry, the method of 'with and with' experiments were designed where the FSUGSM was integrated one time step forward, then followed by a suppression of a component of either the model's physics or dynamics and again followed by a forward integration in time. This was done for each component of the model. At each time-step the same component of the model was removed to preserve continuity and the large-scale tendencies of the model were collectively saved. At the conclusion of a 120 hour forecast, one is left with a series of gridded forecasts that indicate the track of the storm, provided one component of the model is suppressed - thus preserving the nonlinear dynamic interactions that occur inside a hurricane as in addition to maintaining the 'with and with' notion.

Given earlier work and preliminary runs of the FSUGSM, the large-scale dynamics appears to play a significantly larger role in the overall recurving residue-free budget of the selected storms. The components of the physics within the storm play a somewhat smaller part in the cumulative storm motion, however it is likely that this component has greater reaching effects when considering the intensity of a storm. Rather erroneous conclusions are drawn if these budgets had been cast with respect to a 'with and without' notion, where nonlinear interaction would have dominated the results.