Changes in Tropical Cyclones Undergoing Extratropical Transition in a Warming Climate: Quasi‐Idealized Numerical Experiments of North Atlantic Landfalling Events.

The current study extends earlier work that demonstrated future extratropical transition (ET) events will feature greater intensity and heavier precipitation to specifically consider potential changes in the impacts of landfalling ET events in a warming climate. A quasi‐idealized modeling framework allows comparison of highly similar present‐day and future event simulations; the model initial conditions are based on observational composites, increasing representativeness of the results. The future composite ET event features substantially more impactful weather conditions in coastal areas, with heavier precipitation and greater storm intensity. Specifically, a Category 2 present‐day storm attained Category 4 Saffir‐Simpson intensity in the future simulation and maintained greater intensity throughout the entire life cycle, although the storm undergoes less reintensification during the post‐ET process, a result of reduced baroclinic conversion. These findings suggest increased potential for coastal hazards due to stronger tropical cyclone winds and heavier rainfall, leading to more severe coastal flooding and storm surge. Plain Language Summary: Earlier studies demonstrate that climate change can amplify the strong winds and heavy rainfall accompanying tropical cyclones (TCs) that are undergoing transformation into midlatitude cyclones. The current study extends earlier work, which focused on oceanic TCs, to specifically consider potential changes in the impacts of landfalling transformation events in a warming climate. The future events feature substantially more impactful weather conditions in coastal areas with heavier rainfall and greater storm intensity. In particular, we find that a Saffir‐Simpson Category 2 tropical storm in present‐day conditions becomes a Category 4 storm in the future, resulting in more extreme weather conditions along high‐latitude coastlines throughout its entire life cycle, even though the storm undergoes less reintensification after it completes the transformation, due to reduced future temperature contrasts in the lower atmosphere The possibility of compound coastal hazards, including stronger winds, lower central pressure, and heavier rainfall, also indicates a heightened risk of coastal flooding and storm surges. Key Points: Substantially stronger winds attributed to the intensified transitioning storm are evident, impacting the U.S. East Coast in the futurePrecipitation analysis features substantial future increases in total rainfall associated with the transitioning storm along the East CoastIn the innermost storm core region, rainfall increased at a rate more than double that predicted by Clausius‐Clapeyron scaling [ABSTRACT FROM AUTHOR]