HWRF HDFL/HD12 Comparison


The Hurricane Weather Research and Forecasting model (HWRF) is a limited-area numerical model used by the National Weather Service (NWS) to provide numerical guidance for operational tropical cyclone forecasting. The atmospheric component of HWRF employs the Non-Hydrostatic Model (NMM) dynamic core of of Weather Research and Forecasting (WRF) model. The oceanic component of HWRF is the Princeton Ocean Model for Tropical Cyclones (POM-TC).

The NWS is always seeking to advance the HWRF forecast skill and, in 2012, it partnered with the Developmental Testbed Center (DTC) to evaluate an alternate configuration of the model with modified fluxes of momentum, sensible and latent heat in POM-TC. The operational configuration of HWRF was tuned a few years ago to achieve superior performance. In that process, fluxes in POM-TC were truncated to 75% of their value, partially to compensate for the transfer of momentum to waves, an important physical process that is not currently represented in HWRF. A direct consequence of reduced fluxes in POM-TC is that mixing is decreased and upward transport of cold water is diminished. Since the atmosphere-ocean system is non-linear, these changes go on to impact various other physical processes.

Since the original tuning of HWRF a few years ago, many changes in model initialization, dynamics, and physics have been introduced. This suggests that the flux truncation may no longer be necessary to achieve superior results, and the use of the full, physically-based, fluxes may be possible.

For this test, the DTC ran retrospective forecasts for the 2012 season using two configurations of HWRF. The HD12 configuration is very similar to the HWRF 2012 operational implementation. The HDFL configuration differs from the HD12 in only one aspect: the fluxes in POM-TC are restored to the 100% value.