The overland reintensification of North Atlantic Tropical Cyclone Erin (2007): physical and dynamical characteristics

North Atlantic Tropical Cyclone Erin (2007) is perhaps best remembered for its brief yet dramatic reintensification period over western and central Oklahoma early on 19 August 2007. During this period of time, or approximately two and a half days after landfall, the cyclone acquired an eye-like structure and regained tropical storm strength with maximum 1-minute sustained winds estimated at over 25 m s-1 at peak intensity. The study of Arndt et al. (2009, BAMS) details further observations of the cyclone during the reintensification period and briefly discusses potential mechanisms behind the reintensification itself.

The focus of this presentation is upon the recreation of the observed evolution using a mesoscale modeling approach and upon identifying the physical and dynamical mechanisms behind the overland reintensification. As noted in the companion presentation (Schumacher et al.), the simulated and observed reintensification process occurs as intense convective development occurs immediately to the east of the simulated cyclone center. Vorticity budgets suggest that this convection tilts and stretches ambient buoyancy-generated horizontal relative vorticity; after this occurs, axisymmeterization of vertical relative vorticity elements about the broad center of the cyclone results in the formation of an intense, nearly axisymmeteric ring of relative vorticity in the boundary layer. Similar evolutions are noted between reintensifying and non-reintensifying cases with differences lying in the vigor of the convective activity and thus the vertical relative vorticity generation and axisymmeterization process. The location of the cyclone with respect to the left exit region of the lower tropospheric jet appears to focus this convection close enough to the center for this axisymmeterization process to occur.

Connections will be drawn within the presentation between Erin's reintensification and developing tropical cyclones and continental mesoscale convective vortices to attempt to conclusively determine the proper taxonomy for the remnant Erin circulation over Oklahoma on 19 August 2007.