Assessing the Fidelity of Landfalling Tropical Cyclone Convective‐Scale Environments in the Warn‐On‐Forecast System Using Radiosondes.

Forecasts of tropical cyclone (TC) tornadoes are less skillful than their non‐TC counterparts at all lead times. The development of a convection‐allowing regional ensemble, known as the Warn‐on‐Forecast System (WoFS), may help improve short‐fused TC tornado forecasts. As a first step, this study investigates the fidelity of convective‐scale kinematic and thermodynamic environments to a preliminary set of soundings from WoFS forecasts for comparison with radiosondes for selected 2020 landfalling TCs. Our study shows reasonable agreement between TC convective‐scale kinematic environments in WoFS versus observed soundings at all forecast lead times. Nonetheless, WoFS is biased toward weaker than observed TC‐relative radial winds, and stronger than observed near‐surface tangential winds with weaker winds aloft, during the forecast. Analysis of storm‐relative helicity (SRH) shows that WoFS underestimates extreme observed values. Convective‐scale thermodynamic environments are well simulated for both temperature and dewpoint at all lead times. However, WoFS is biased moister with steeper lapse rates compared to observations during the forecast. Both CAPE and, to a lesser extent, 0–3‐km CAPE distributions are narrower in WoFS than in radiosondes, with an underestimation of higher CAPE values. Together, these results suggest that WoFS may have utility for forecasting convective‐scale environments in landfalling TCs with lead times of several hours. Plain Language Summary: Landfalling tropical cyclones (known as tropical depressions, tropical storms, or hurricanes) often spawn tornadoes, which are more challenging to forecast than Great Plains tornadoes. The development of a weather forecast ensemble model, known as the Warn‐on‐Forecast system, may help improve tornado forecasts. This study compares vertical profiles of winds, temperature, moisture, and associated severe weather metrics from the Warn‐on‐Forecast with observed radiosonde data (i.e., balloon‐borne instruments) in landfalling tropical cyclones. Our analysis shows agreement between the observed and forecasted vertical structure of TC winds at all lead times including strong changes in near‐surface wind speed and direction. Nonetheless, forecasted tropical cyclone winds tend to be biased weaker than observed, which is associated with an underestimation of environmental favorability for tornadoes. Similarly, forecasted temperature and moisture are also reasonably represented compared to observations. However, Warn‐on‐Forecast tends to overestimate moisture and near‐surface temperature, with smaller‐than‐observed variability in thermodynamic environmental favorability. Together, these results suggest that the weather forecast model used here may be useful for improving forecasts of supercell environments in landfalling TCs. Key Points: Warn‐on‐Forecast tropical cyclone forecasts show reasonable agreement between observed and forecast convective‐scale kinematic environmentsForecast convective‐scale thermodynamic environments also show reasonable fidelity compared to observationsA case study shows stronger discrepancies than the full sample including weaker than observed winds, temperature inversions, and dry layers [ABSTRACT FROM AUTHOR]