Evolving low-wavenumber flows and the distribution of deep eyewall convection during the rapid intensification of Hurricane Guillermo (1997)

Recent observations and numerical simulations indicate that the azimuthal distribution of deep eyewall convection can be significantly influenced by the environmental vertical wind shear and internal dynamical processes. In such instances, the convection can acquire a persistent low-azimuthal wavenumber structure composed of multiple transient convective cells. The roles played by such convective asymmetries in hurricane evolution are not well understood. In particular, the extent to which evolving low-wavenumber flow within the inner core influences the generation, organization, and evolution of asymmetric convection remains an open question. The objective of this study is to elucidate the organization and evolution of observed asymmetric eyewall convection within the context of the low-wavenumber flows within and near the eyewall of a rapidly intensifying hurricane.

This study utilizes an extensive Doppler radar dataset collected during multiple dual-aircraft penetrations of Hurricane Guillermo during a 5 hour period on 2 August 1997. A total of 10 unique dual-Doppler analyses are used to document the evolving convective and kinematic structures within and near the eyewall. During this time, the inner core exhibited a vorticity structure supportive of barotropic/baroclinic instabilties. The eyewall exhibited a persistent wavenumber-one convective pattern consistent with the observed moderate northerly vertical wind shear. The eyewall also contained a rich spectrum of evolving higher-wavenumber kinematic structures and deep convective cells, particularly during a series of asymmetric convective bursts lasting ~2 hours. Currently, spatial and temporal relationships between the prominent asymmetric flows and the episodic convective bursts are being documented. The structure and impact of evolving mesovortical flows is also being examined, as well as mass exchanges across the eye-eyewall interface. A synopsis of our preliminary results and their comparison with previous studies will be presented at the conference.