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Supercells in landfalling tropical cyclones (TCs) often produce tornadoes that can cause fatalities and extensive damage. In previous studies, many tornadoes have been shown to form <50 km from the coast, and their parent storms may also intensify as they cross the coastal boundary. This study uses WSR‐88D observations of TC tornadic mesocyclones from 2011 to 2018 to examine changes in their low‐level rotation upon moving onshore. We will show that radar‐derived azimuthal shear tends to increase in storms that cross the coastal boundary. Similar intensification trends are also found in radar‐derived (supercell) storm‐scale divergence, such that storm‐scale convergence increases as storms move onshore. It is likely changes in the near‐coast vertical wind shear and/or near‐shore convergence helps explain supercell intensification, which is important to consider particularly in operational settings.

 

Abstract The hurricane boundary layer (HBL) has been observed in great detail through aircraft investigations of tropical cyclones over the open ocean, but the coastal transition of the HBL has been less frequently observed. During the landfall of Hurricane Irene (2011), research and operational aircraft over water sampled the open-ocean HBL simultaneously with ground-based research and operational Doppler radars onshore. The location of the radars afforded 13 h of dual-Doppler analysis over the coastal region. Thus, the HBL from the coastal waterways, through the coastal transition, and onshore was observed in great detail for the first time. Three regimes of HBL structure were found. The outer bands were characterized by temporal perturbations of the HBL structure with attendant low-level wind maxima in the vicinity of rainbands. The inner core, in contrast, did not produce such perturbations, but did see a reduction of the height of the maximum wind and a more jet-like HBL wind profile. In the eyewall, a tangential wind maximum was observed within the HBL over water as in past studies and above the HBL onshore. However, the transition of the tangential wind maximum through the coastal transition showed that the maximum continued to reside in the HBL through 5 km inland, which has not been observed previously. It is shown that the adjustment of the HBL to the coastal surface roughness discontinuity does not immediately mix out the residual high-momentum jet aloft. Thus, communities closest to the coast are likely to experience the strongest winds onshore prior to the complete adjustment of the HBL. 

A ground‐based C‐band Shared Mobile Atmospheric Research and Teaching (SMART) polarimetric radar and the National Weather Service WSR‐88D radar near Wilmington, North Carolina simultaneously observed Hurricane Florence (2018) as it made landfall as a category 1 hurricane. The slow translation of Florence allowed for more than 30 hr of data collection before, during and after the tropical cyclone came ashore. Nearly 26 hr of three‐dimensional wind retrievals every 6–10 min were constructed from the radar observations, providing an unprecedented view of the evolution of rainbands, the inner core and the eyewall of Hurricane Florence. This article describes the radar data, the procedures used for automated quality control, data processing and the wind retrievals that have been constructed. The location of the data and wind retrieval archive is given. These data can be used to study the dynamics and rainfall of Hurricane Florence, to quantify the impact of winds on the natural and built environment, to validate numerical simulations of the tropical cyclone, and as an educational resource for courses in radar and tropical meteorology.

 

This article describes a unique ground‐based weather radar dataset collected during the landfall of Hurricane Harvey (2017) along the United States Gulf Coast, documents the wind retrievals conducted with this dataset, and reports on the location of the archive of the data and wind retrievals so that others may gain access and use of these data. Datasets from C‐band dual‐polarimetric Shared Mobile Atmospheric Research and Teaching (SMART) radar and the United States National Weather Service WSR‐88D in Corpus Christi, Texas, are presented, along with dual‐Doppler analyses before and during Harvey's landfall on the United States Gulf Coast. The quality assurance and dual‐Doppler wind synthesis procedures are detailed. Nearly 8 hr of dual‐Doppler wind analyses were constructed, providing an unprecedented dataset for use in understanding hurricane dynamics at landfall and validating numerical simulations of Hurricane Harvey. In addition, raw, dual‐polarization data not used in the dual‐Doppler syntheses, but included in each radar dataset, are also summarized.

 

A mobile Shared Mobile Atmospheric Research and Teaching (SMART) radar was deployed in Hurricane Harvey and coordinated with the Corpus Christi, TX, WSR‐88D radar to retrieve airflow during landfall. Aerodynamic surface roughness estimates and a logarithmic wind profile assumption were used to project the 500‐m radar‐derived maximum wind field to near the surface. The logarithmic wind assumption was justified using radiosonde soundings taken within the storm, while the radar wind estimates were validated against an array of StickNets. For the data examined here, the radar projections had root‐mean‐squared error of 3.9 m/s and a high bias of 2.3 m/s. Mesovorticies in Harvey's eyewall produced the strongest radar‐observed winds. Given the wind analysis, Harvey was, at most, a Category 3 hurricane (50–58 m/s sustained winds) at landfall. This study demonstrates the utility of integrated remote and in situ observations in deriving spatiotemporal maps of wind maxima during hurricane landfalls.

 

Deep convective transport of gaseous precursors to ozone (O₃) and aerosols to the upper troposphere is affected by liquid phase and mixed‐phase scavenging, entrainment of free tropospheric air and aqueous chemistry. The contributions of these processes are examined using aircraft measurements obtained in storm inflow and outflow during the 2012 Deep Convective Clouds and Chemistry (DC3) experiment combined with high‐resolution (dx≤3 km) WRF‐Chem simulations of a severe storm, an air mass storm, and a mesoscale convective system (MCS). The simulation results for the MCS suggest that formaldehyde (CH₂O) is not retained in ice when cloud water freezes, in agreement with previous studies of the severe storm. By analyzing WRF‐Chem trajectories, the effects of scavenging, entrainment, and aqueous chemistry on outflow mixing ratios of CH₂O, methyl hydroperoxide (CH₃OOH), and hydrogen peroxide (H₂O₂) are quantified. Liquid phase microphysical scavenging was the dominant process reducing CH₂O and H₂O₂outflow mixing ratios in all three storms. Aqueous chemistry did not significantly affect outflow mixing ratios of all three species. In the severe storm and MCS, the higher than expected reductions in CH₃OOH mixing ratios in the storm cores were primarily due to entrainment of low‐background CH₃OOH. In the air mass storm, lower CH₃OOH and H₂O₂scavenging efficiencies (SEs) than in the MCS were partly due to entrainment of higher background CH₃OOH and H₂O₂. Overestimated rain and hail production in WRF‐Chem reduces the confidence in ice retention fraction values determined for the peroxides and CH₂O.