Investigating Tropical Cyclone Rapid Intensification Using Idealized Simulations with Realistic Initial Vortices

There is observational evidence that tropical storms with a smaller inner core are more likely to undergo rapid intensification (RI), and idealized simulations indicate that the timing of RI is systematically sensitive to the radius of maximum winds (RMW) in the prescribed initial vortex. Previous idealized modeling studies have also found that the rate of intensification is sensitive to both the initial RMW and the radial decay rate of tangential wind speed outside of the RMW. The initial vortex in idealized simulations (and in operational forecasts that use vortex “bogussing”) generally have a well-defined RMW, with a relatively sharp radial decay rate of tangential wind outside of the RMW. In contrast, observed TCs prior to the onset of intensification often have very flat wind profiles, without a clearly defined wind speed maximum.

In this study, we investigate the timing of RI and the rate of intensification during RI using idealized simulations with more realistic initial vortex profiles. We construct radial profiles based off of several observed cases of weak tropical storms sampled prior to and near the onset of intensification, and we examine the degree to which variability in RI timing and intensification rate relate to realistic variability in initial vortex structure. We also investigate the influence of initializing a vortex with a well-defined RMW (as opposed to a broad profile without a well-defined maximum) on the subsequent RI. Finally, we examine the degree to which the ultimate inner-core size is influenced by the existence of an initial well-defined RMW, and the degree of natural variability in inner-core size that is induced by an initial vortex without a well-defined RMW.