Numerical simulations of the formation of Hurricane Gabrielle (2001)

The first sensitivity experiment removes the initial (or precursor) disturbance, a midtropospheric vortex located over Florida. The second sensitivity experiment reduces the vertical wind shear over the area of formation. The control run produces a system comparable to Gabrielle.

The convection in the control run is consistently located downshear of the center of circulation. In the first sensitivity experiment, with the removal of the initial disturbance, no organized system develops. This indicates the importance of the midtropospheric vortex in Gabrielle's formation.

The second sensitivity experiment, which reduces the vertical wind shear over the area of Gabrielle's formation, produces a system that can be identified as Gabrielle. This system, however, is weaker than both the control run and the observations of Gabrielle. This study provides direct evidence of a favorable influence of modest vertical wind shear on the formation of a tropical cyclone in this case.