Impacts of Environmental Wind Shear Effect Parameterization and TKE-dependent Entrainment Enhancement in the Convective Updrafts on Hurricane Intensity and Track Forecasts

The parameterized planetary boundary layer (PBL) and cumulus convection schemes have large impacts on hurricane intensity and track forecasts. The updraft and velocity equations in the National Centers for Environmental Prediction's (NCEP) Global Forecast System (GFS) PBL and convection schemes are composed of parcel’s buoyancy as a source term and entrainment from the environment as a sink term. The environmental wind shear would tilt the parcel horizontally during its upward motion, leading to reduction of the vertical component of its velocity and consequently, reducing vertical convective transport of momentum. In this study, we develop a parameterization to include environmental wind shear effect in the updraft velocity equation as a sink term. On the other hand, strong turbulence in high winds would largely enhance entrainment into the convective updrafts. The current GFS cumulus convection scheme allows only a limited enhancement of entrainment for a larger turbulent kinetic energy (TKE). In this study, we further enhance the entrainment rate in the convective updrafts proportional to TKE when TKE is larger than a threshold value. We explore the impacts of the new parameterization of environmental wind shear effect and TKE-dependent entrainment enhancement in the convective updrafts on hurricane intensity and track forecasts in the NCEP GFS and Hurricane Analysis and Forecast System (HAFS).