Assessment of Tropical Cyclone Kinematic and Thermodynamic Structures in the North American Regional Reanalysis

The North American Regional Reanalysis (NARR) is a data-rich resource for hydrometeorology research, with potential application toward a better understanding of the coupled interaction between tropical cyclones (TCs) and large-scale moisture. However, there is a lack of research into the authentic representation of TCs within the NARR. Because of the relatively low horizontal resolution, it is unclear whether reanalysis models capture the sub-gridscale convective processes that are crucial to TC energetics and that interact with the larger-scale environment. The purpose of this paper is to determine the suitability of examining TC water budgets and large scale thermodynamics using the NARR, toward an ultimate objective of a better understanding of TC precipitation during landfall. The present study investigates large-scale kinematic and thermodynamic structures in U.S. landfalling TCs during 1998-2012. TC positions are determined based on three parameters: sea level pressure, 850 mb vorticity, and 700-200 mb thickness anomalies. The track error is frequently constrained to within 100 km as compared with best track observations. TCs with stronger intensities have the most accurate tracks while degraded tracks occur near the domain boundary and high terrain. To investigate TC structure, Hurricane Katrina (2005), Hurricane Dolly (2008), and Tropical Storm Fay (2008) are chosen as individual case studies to represent a cross section of TC size/intensity and larger-scale environmental moisture regimes. The larger kinematic structure is compared with TC size metrics in the extended best track dataset. Three-dimensional warm core structure is evaluated using thickness anomalies, environmental temperature anomalies and equivalent potential temperature. In all case studies, the warm core and large-scale wind field respond in a dynamically consistent fashion with respect to the larger-scale environment. Cross sections of temperature anomalies match closely with those expected for a warm core TC, with upper tropospheric values of approximately 8-10°C analyzed in Hurricane Katrina (2005). Therefore, it is determined that the large-scale TC structure is sufficiently represented in the recent sample of U.S. landfalling TCs. Based on these results, we find that the NARR dataset represents TC structures and their surrounding environments sufficiently well despite poorly resolved inner core structures. Future research will investigate the evolution of TC moisture budgets in the period around landfall.