Airborne Doppler Radar Observations of Tropical Cyclone Boundary Layer Kinematic Structure and Evolution During Landfall

Airborne Doppler radar observations of the wind field in the tropical cyclone boundary layer (TCBL) during the landfall of Hurricane Ida (2021) are examined here. Asymmetries in tangential and radial flow are governed by tropical cyclone (TC) motion and vertical wind shear prior to landfall, while frictional effects dominate the asymmetry location during landfall. Strong TCBL inflow on the offshore-flow side of Ida occurs during landfall, while the location of the peak tangential wind at the top of the TCBL during this period is located on the onshore-flow side. A comparison of these observations with a numerical simulation of TC landfall shows many consistencies with the modeling study, though there are some notable differences that may be related to differences in the characteristics of the land surface between the simulation and the observations here. The structure of the wind field in the lowest levels of a hurricane when it makes landfall plays a significant role in determining damage. This study uses aircraft observations to document the changes that occur in the winds in the lowest levels of a hurricane prior to and as it makes landfall. The location of the strongest inflow into the storm center and winds around the center are determined by characteristics like storm motion and environmental winds when the storm is over open water, but at landfall these wind peaks are dominated by the differences in friction between the land surface and water. At landfall, the inflow near the surface is strongest on the side of the hurricane experiencing offshore flow, while winds moving around the storm center a few thousand feet above the surface are strongest on the side experiencing onshore flow. These results are mostly consistent with computer modeling studies, allowing for studies on physical processes to be conducted using these models. Wind structure in the hurricane boundary layer shows significant asymmetries over water and at landfallThe nature of these asymmetries changes significantly during landfallAircraft observations of these changing asymmetries support recent modeling studies and point toward physical processes for their evolution