Finescale spiral band features within a numerical simulation of hurricane opal (1995)

One of the most recognizable features associated with a well-organized tropical system are spiral rainbands. These quasi-stationary rainbands often extend hundreds of kilometers from the storm center and have been well described in the literature. Observational studies have since identified additional banding structures, including outward-propagating small-scale spiral bands. These rainbands may have considerable implications for "core type" tornadoes, local wind maxima associated with downburst damage swaths, as well as a role in overall hurricane dynamics. As such, here a numerical simulation of Hurricane Opal (1995) is examined with unprecedented resolution necessary to capture these small-scale spiral bands. Opal was an intense landfalling hurricane that demonstrated small-scale spiral banding features analogous to those observational studies. The scale and characteristics of the simulated bands are consistent with observed small-scale spiral banding of intense hurricanes. A varietal of Kelvin-Helmholtz instability combined with boundary layer shear is offered as the most plausible dynamical mechanism for the generation and maintenance of these propagating bands outward of the eyewall region.