Inner Core Processes Leading to the Intensification of Hurricane Harvey
The dual-polarimetric Shared Mobile Atmospheric Research and Teaching (SMART) radar (SR2) collected observations of Hurricane Harvey’s inner core from 2055 UTC on 25 August 2017 until 1440 UTC on 26 August 2017. The WSR-88D in Corpus Christi, TX (KCRP) was approximately 50 km from SR2, affording a dual-Doppler wind retrieval region over Port Aransas, Rockport, and the Gulf of Mexico. Harvey’s inner core and eye passed through the eastern dual-Doppler lobe, resulting in the retrieval of the three-dimensional wind field from near-synchronous observations between SR2 and KCRP.
A temporal evolution of Harvey’s wind field will be presented, focusing on the role of asymmetric vortex Rossby waves (VRWs) in Harvey’s eyewall in the axisymmetrization process and local wind maxima. Previous SMART radar observations in Hurricanes Isabel (2003), Irene (2011), Hermine (2016), and Matthew (2016) verified the modeling-hypothesized presence of outward-propagating spiral VRWs. These spiral, convectively coupled waves were inferred to be resultant of the axisymmetrization processes near the radius of maximum wind (eyewall). Due to Harvey’s compact inner core, dual-Doppler observations cover both the eyewall and a large portion of the inner core region radially outward of the eyewall.
Initial results from center-relative projections of Harvey’s tangential and radial wind field suggest that VRWs near the radius of maximum wind result in both inward and outward transport of momentum on the downwind and upwind portions of the waves respectively. Between 2055 and 2300 UTC, outward-propagating trailing VRWs were observed in the inner core similar to results of previous SMART radar observations. Coincident with these observations, Harvey appeared to axisymmetrize as the storm reached its peak intensity before landfall. Modeling studies indicate the axisymmetrization process should lead to intensification, but has not been previously observed in high temporal resolution. After such a process, the extreme shear of the horizontal wind appeared to suppress the outward propagation of trailing spiral VRWs. However, VRWs (or mesovorticies) in the eyewall continued to evolve during landfall, resulting in local winds at 500 m that exceeded most wind observations offshore at the same level. In addition to SMART radar observations, a National Severe Storms Laboratory Mobile Mesonet conducted a transect of the inner core. Ground-based in situ wind and pressure observations beneath a rapidly sheared outward-propagating VRW will be presented in context to the mesoscale wind observations aloft via dual-Doppler analysis.