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

Winds in the boundary layer (BL) of a landfalling tropical cyclone (TC) can cause significant damage, even as winds decay inland. Winds in the TCBL also govern storm surge and rainfall fields, two key sources of damage during TC landfall. Understanding the physical processes that govern the structure and evolution of TCBL winds is therefore critical to predict TC structure and intensity as well as impacts at and after landfall.

Airborne Doppler radar observations of the wind field in the TCBL during the landfall of Hurricane Ida (2021) are examined here, with an emphasis on the evolution of asymmetries in boundary-layer tangential and radial flow prior to and during landfall. Asymmetries in tangential and radial flow are governed by 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 recent numerical simulations 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.