P58     Evaluation of the MYNN planetary boundary layer scheme in the Hurricane Weather Research and Forecast (HWRF) system.

Kalina, Evan, Cooperative Institute for Research in Environmental Sciences (CIRES) and National Oceanic and Atmospheric Administration (NOAA)/Global Systems Division (GSD), Robert Fovell, State University of New York-Albany, Mrinal Biswas, Kathryn Newman, National Center for Atmospheric Research (NCAR), Evelyn Grell, CIRES and NOAA/Physical Sciences Division, Laurie Carson, NCAR, and James Frimel, Cooperative Institute for Research in the Atmosphere and NOAA/GSD

Numerical simulations of tropical cyclones are known to be sensitive to the parameterization of the planetary boundary layer (PBL), especially to the vertical profile of eddy mixing, which impacts the strength and depth of the radial inflow into the storm. The Hurricane Weather Research and Forecast system (HWRF) is one of NOAA's operational hurricane models and currently uses the Global Forecast System (GFS) Eddy Diffusivity-Mass Flux (EDMF) PBL scheme. The impact of replacing this scheme with the Mellor-Yamada-Nakanishi-Niino (MYNN) PBL scheme on the numerical representation of four 2018 North Atlantic tropical cyclones is tested. Comparisons of the tropical cyclone track and intensity forecasts between the two HWRF configurations show generally comparable performance. However, HWRF-MYNN produces vertical profiles of temperature and wind velocity in the hurricane eyewall that compare more favorably with dropsonde observations. This improvement is driven largely by increased eddy mixing in HWRF-MYNN, which is nearly three times larger in the 800–1500 m layer than in HWRF-GFS EDMF.