WRF FOR HURRICANES OVERVIEW
Description of HWRF
The Hurricane Weather Research and Forecast system (HWRF) has been operational at NCEP since 2007. This advanced hurricane prediction system was developed primarily at the NWS/NCEP's Environmental Modeling Center (EMC), in collaboration with NOAA GFDL, NOAA AOML, and the University of Rhode Island, taking advantage of the WRF model infrastructure developed at NCAR. HWRF is a state-of-the-art hurricane model that has the capability to address the intensity, structure, and rainfall forecast problems. It is currently used to provide realtime numerical guidance in all oceanic basins.
The HWRF model is a primitive equation, non-hydrostatic coupled atmosphere-ocean model. The model uses the Non-hydrostatic Mesoscale Model (NMM) dynamic core, including its rotated latitude-longitude projection with E-grid staggering. Starting 2018, the model has an outer domain spanning about 77.2° x 77.2°, with two telescopic two-way interactive nest domains. The intermediate and inner nests, which move with the storm, cover areas of approximately 17.8° x 17.8° and 5.9° x 5.9° respectively. The stationary parent domain has a grid spacing of 0.099° (about 13.5 km), the intermediate nest 0.033° (about 4.5 km), and the inner nest domain 0.011° (about 1.5 km).
The model physics includes a Scale Aware Simplified Arakawa-Schubert scheme for cumulus parameterization and the Ferrier-Aligo cloud microphysics package for explicit condensation. The Global Forecast System (GFS) Hybrid-Eddy Diffusivity Mass Flux planetary boundary layer parameterization is used. An upgraded GFDL model surface layer scheme, along with Noah land surface model, is used to compute surface fluxes. Radiation physics are evaluated by the RRTMG scheme.
The NCEP GFS analysis, the NCEP GDAS 6-h forecasts, and the storm message provided by NHC are used to generate initial conditions for the hurricane model. The HWRF system does not use a bogus vortex. Instead, it contains a forecast/analysis cycle in which a 6-h HWRF forecast from the previous cycle is used in a vortex relocation procedure, after being adjusted for position, structure and intensity using the NHC storm message. After the vortex relocation, the initial conditions are further refined through the use of a 3D hybrid ensemble-variational data assimilation system. The GFS forecasted fields every 6 hours are used to provide lateral boundary conditions during each forecast.
In the North Atlantic, Eastern North Pacific, Western North Pacific, Central Pacific, and North Indian Ocean basins the hurricane model is coupled by default with the Message Passing Interface Princeton Ocean Model (MPIPOM-TC). The model can also be run in coupled mode in any ocean basin worldwide. The MPIPOM-TC is initialized by a diagnostic and prognostic spinup of the ocean circulations using available climatological ocean data in combination with real-time sea surface temperature and sea surface height data. In the Atlantic basin, realistic representations of the structure and positions of the Loop Current, Gulf Stream, and warm- and cold-core eddies are incorporated in the spin up phase.
In the North Atlantic, Western North Pacific, North Indian Ocean basins the ocean is initialized with Generalized Digital Environmental Model (GDEM) climatology whereas in the Eastern Pacific and Central Pacific basins the initialization is done using the Real-Time Ocean Forecast System (RTOFS) data by default.
At this time, the Developmental Testbed Center (DTC) supports the following components of HWRF:
- WRF v4.0a (contains the 2018 operational capability)
- Global modeling preprocessing with prep_hybrid and the WRF Preprocessing System (WPS)
- Vortex Initialization
- Gridpoint Statistical Interpolation (GSI) data assimilation system
- NCEP Coupler
- MPIPOM-TC and its initialization
- HWRF Post-processing
- GFDL Vortex Tracker
- Running scripts
- Idealized capability
For more information, please refer to the operational HWRF page.
HWRF IDEALIZED OVERVIEW
Description of HWRF Idealized
The Hurricane Weather Research and Forecast system (HWRF) Idealized capability is distributed with version 4.0a.
The HWRF model has two classes of initialization: a) ideal vortex and b) real data. For more information on how to build and run HWRF, please refer to the User's Guide.
The HWRF Idealized capability include a landfall option. Currently only GFDL Slab land surface physics option is supported for landfall capability and efforts are underway to include other land-surface physics options. A namelist file for land surface configuration introduces a switch for landfalling capability, specifies the type of land surface, initial land-surface temperature to be used over land. The default configuration introduces a homogeneous land surface but can be modified to account for heterogeneity through the source code. The direction of land motion can also be chosen. Two options are available – West to East or East to West.
At the time of HWRF v4.0a release, the landfall capability is broken. DTC is working on the fix. As soon as it is available, a patch will be released.
The idealized simulation requires 00-h and 120-h GFS GRIB2 forecasts, along with a sounding, specifications of the initial vortex, and a namelist. The idealized simulation is performed on the operational triple nested domain configuration, with grid spacings of 13.5-, 4.5- and 1.5-km. All the operational atmospheric physics, as well as the supported experimental physics options in HWRF, can be utilized in the idealized framework. The post processing can be done using the Unified Post-Processor.
Always look for Known Issues before setting up any experiment
For the convience of the user community, sample GFS GRIB2 files for running the idealized case are provided.
For more information, please refer to the HWRF User's Guide.