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This study presents a method to diagnose radial ventilation, the horizontal flux of relatively low-θ_eair into tropical cyclones, from dropsonde observations. We used this method to investigate ventilation changes over three consecutive sampling periods in Hurricane Sam (2021), which underwent substantial intensity changes over 3 days. During the first and last periods, coinciding with intensification, the ventilation was relatively small due to a lack of spatial correlation between radial flow andθ_eazimuthal asymmetries. During the second period, coinciding with weakening, the ventilation was relatively large. The increased ventilation was caused by greater shear associated with an upper-level trough, tilting the vortex, along with dry, low-θ_eair wrapping in upshear. The spatial correlation of the radial inflow and anomalously low-θ_eair resulted in large ventilation at mid- to upper levels. Additionally, at low to midlevels, there was evidence of mesoscale inflow of low-θ_eair in the stationary band complex. The location of these radial ventilation pathways and their effects on Sam’s intensity are consistent with previous idealized and real-case modeling studies. More generally, this method offers a way to monitor ventilation changes in tropical cyclones, particularly when there is full-troposphere sampling around and within a tropical cyclone’s core.

The physical processes that govern eyewall replacement cycles (ERCs) in tropical cyclones (TCs) are not yet fully understood. In particular, asymmetric structures within the TC inner core have an uncertain role in ERC dynamics. This study analyzes the kinematic and precipitation asymmetric structures during successive ERCs in Hurricane Ivan (2004) using airborne Doppler radar observations. The azimuthal locations of these asymmetries are analyzed relative to the deep-layer (850–200 hPa) environmental wind shear vector. Two ERCs were analyzed at different stages of their evolution. During the concentric eyewall stage of the first ERC, the outer eyewall updrafts were strongest in the left-of-shear half, which also coincided with mesoscale descending inflow (MDI) just radially outward. Enhanced low-level convergence, updrafts, and MDI were collocated in a zone spiraling inward toward the strongest outer eyewall updrafts, suggesting that the vertical velocity asymmetry in the outer eyewall was possibly forced by a stratiform-induced cold pool similar to MDI impacts seen in past TC studies. During the final stage of the second ERC, the outer eyewall (now the singular primary eyewall) experienced an upwind shift in the precipitation and vertical velocity asymmetries. The updraft maximum shifted from the downshear-left quadrant to the downshear-right quadrant, and the precipitation maximum (downwind of the updraft maximum) shifted from left-of-shear to the downshear direction. This shift corroborates previous studies, which hypothesize that at the end of an ERC, the forcing mechanism that drives the eyewall vertical velocity asymmetry transitions from MDI/cold-pool processes to direct interaction with the environmental wind shear.

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.

Supercells in landfalling tropical cyclones (TCs) often produce tornadoes within 50 km of the coastline. The prevalence of TC tornadoes near the coast is not explained by the synoptic environments of the TC, suggesting a mesoscale influence is likely. Past case studies point to thermodynamic contrasts between ocean and land or convergence along the coast as a possible mechanism for enhancing supercell mesocyclones and storm intensity. This study augments past work by examining the changes in the hurricane boundary layer over land in the context of vertical wind shear. Using ground-based single- and dual-Doppler radar analyses, we show that the reduction in the boundary layer wind results in an increase in vertical wind shear/storm-relative helicity inland of the coast. We also show that convergence along the coast may be impactful to supercells as they cross the coastal boundary. Finally, we briefly document the changes in mesocyclone vertical vorticity to assess how the environmental changes may impact individual supercells.

Understanding physical processes leading to rapid intensification (RI) of tropical cyclones (TCs) under environmental vertical wind shear is key to improving TC intensity forecasts. This study analyzes the thermodynamic processes that help saturate the TC inner core before RI onset using a column‐integrated moist static energy (MSE) framework. Results indicate that the nearly saturated inner core in the lower‐middle troposphere is achieved by an increase in the column‐integrated MSE, as column water vapor accumulates while the mean column temperature cools. The sign of the column‐integrated MSE tendency depends on the competition between surface enthalpy fluxes, radiation, and vertical wind shear‐induced ventilation effect. The reduction of ventilation above the boundary layer due to vertical alignment is crucial to accumulate the energy within the inner core region. A comparison of the RI simulation with a null simulation further highlights the impact of vortex structure on the thermodynamic state adjustment and TC intensification.