Sensitivity of the NOAA Hurricane Research and Forecasting Model (HWRFX) to Various Cloud and Boundary Layer Parameterizations

As the research and operational communities work together under the auspices of NOAA's Hurricane Forecast Improvement Project (HFIP) to understand the degree to which a tropical storm intensity forecast can be improved by increasing the horizontal grid spacing of operational NWP models, it still remains a great challenge for the research community to reach a consensus on whether the current physics parameterizations in operational NWP models are suitable for horizontal grid spacings of 3 km or smaller. Another challenge is what the minimal vertical resolution should be for a given high horizontal resolution, say 1 km, in an operational setup for tropical storm prediction. To deal with these challenges, it is important to first understand how sensitive operational NWP models for hurricane forecast are to different physics parameterizations and various grid resolutions in both the horizontal and vertical directions.

This presentation highlights major results from a series of idealized experiments with the NOAA Hurricane Research and Forecasting Model (HWRFX). These experiments are performed with horizontal grid spacing of 3 km, and the purpose of the experiments is to reveal how sensitive HWRFX is to commonly used microphysics and boundary-layer parameterization schemes and various horizontal and vertical resolutions. The model is initialized with a weak axisymmetric vortex disturbance in an idealized tropical environment that is favorable for the vortex disturbance to develop into a hurricane. The initial mass and wind fields associated with the weak vortex disturbance are obtained by solving the nonlinear balance equation for the given wind distributions of the initial vortex, and the prescribed background thermal sounding and wind.