HURRICANE MODELING AT EMC
The HWRF group at EMC works in conjunction with members of the Global, Mesoscale, and Marine brances to continually make improvements to the Hurricane Weather Research and Forecast System (HWRF) model for each hurricane season.
Extensive testing and evaluation is completed for each new model configuration before these changes are incorporated into the operational model. Collaboration from organizations like GFDL, DTC, NHC, and HRD is also essential to the hurricane team's progress.
The atmosphere-ocean coupled Hurricane Weather Research and Forecast (HWRF) modeling system runs in the NCEP production suite on the NOAA Central Computer System (CCS), which is planned for transitioning to Weather and Climate Operational Supercomputing System (WCOSS) in July 2013. The HWRF modeling system is developed and supported by the Environmental Modeling Center (EMC) and operated by NCEP Central Operations (NCO). HWRF model consists of multiple movable two-way interactive nested grids that follow the projected path of the storm. As a major step towards providing improved intensity forecast skill, for 2012 hurricane season, the operational HWRF model was configured with triple-nest capability that includes a cloud-resolving inner most grid operating at 3 km horizontal resolution, encompassed by an intermediate grid at 9 km resolution and the outer domain at 27 km resolution. The HWRF model is coupled to 3D Princeton Ocean Model (POM) for the North Atlantic basin and is coupled to 1D POM for the North Eastern Pacific basin. The HWRF model is run each cycle for a maximum of five storms requested by the National Hurricane Center (NHC) for the North Atlantic and North Eastern Pacific basins, and provides 126-hr forecast guidance for hurricane track and intensity at every 3-hr interval and a very high temporal resolution (5sec.) information on location of the storm center and it’s intensity (HTCF). The NCEP Global Forecast System (GFS) analysis and forecasts provide initial and boundary conditions for the HWRF model. An advanced vortex relocation and initialization procedure along with the GSI analysis system is used to generate the initial vortex and environment for the atmospheric HWRF model. POM model incorporates a feature based initialization of oceanic fields during the spin-up phase. An advanced coupler developed at NCEP provides means to exchange information at the air-sea interface of HWRF and POM models.
The objective of the HWRF team is to implement planned scientific and product enhancements to the operational HWRF annually, with an aim towards improved forecast performance using state-of-the-art numerical techniques. The HWRF project is an NCEP Annual Operating Plan (AOP) milestone which maps to NCEP’s strategic goal to produce and deliver the best products and services, and prepare for a Weather Ready Nation.
IMPLEMENTATION INFORMATION
Highlights for HWRF's 2013 implementation include the following:
1. HWRF Infrastructure/Resolution Upgrades: The NMM core of the operational HWRF model will be upgraded to latest community version currently referred to as V3.5a. Due to computational constraints, FY12 HWRF was run with a smaller domain large physics time steps (180 sec. for 3km domain). Proposed FY13 HWRF will have 20% bigger 3km domain and will include higher frequency of physics calls (every 30 sec.). In addition, nest-parent interpolations have been re-designed for improved treatment of nest boundaries and to allow advection of several microphysical variables across the domains. Another resolution related upgrade is to interpolate GDAS/GFS spectral files to 0.25 degree resolution (instead of 0.5 degree) in hwrf_prep_hybrid to get maximum benefit from global analysis and forecasts for HWRF initial and boundary conditions.2. HWRF New Nest Motion Algorithm: The current mass centroid based nest motion algorithm will be replaced with a new storm tracking algorithm using Tim Marchok’s NCEP tracker functionalities. This will eliminate several problems identified with the centroid method, is more efficient in identifying and tracking the tropical systems more accurately, resulting in improved track and intensity forecasts.
3. HWRF Physics Upgrades: HWRF physics upgrades consist of modifications to the GFS PBL based on variable Richardson number following Vickery and Mahrt (2003) for improved PBL structure in hurricanes as well as over land.
4. HWRF Initialization Upgrades: Vortex initialization is modified with further improvements to the storm size correction and resizing the filter domain. For storms weaker than 16m/s, we eliminate the need for bogus by directly using the GFS vortex.
5. HWRF Data Assimilation Upgrades: A major upgrade for 2013 implementation is the 80-member global ensembles based one-way hybrid EnKF-3DVAR data assimilation system for HWRF. 75% weight is given the the ensemble covariances and 25% for the static covariances. First guess fields for the analysis are taken from GDAS forecasts and all conventional datasets are assimilated, with provisions to assimilate real-time inner-core TDR/ FL/SFMR/Dropsonde recon datasets.
6. HWRF Ocean Upgrades: Current operational procedure of 25% truncation for heat, radiation and momentum fluxes is removed in as it is found no longer needed due to improved physics in HWRF. Upgrades to multi-processor MPI-POM with single trans-Atlantic domain and 3D ocean for Eastern Pacific basin were withdrawn from 2013 implementation plans due to lack of sufficient T&E and potential increase in resources required for operational implementation on CCS. On WCOSS, this should not be a problem.
7. HWRF Post-Processing and Product Upgrades: HWRF post processing upgrades include bug fixes for simulated synthetic imagery to reduce domain discontinuities. Apart from very high-temporal resolution track and intensity forecast data at 5-sec. interval (HTCF), ATCF style output at every 9-minute interval will be added to the suite of products.
8. HWRF Script Enhancements and Procedural Upgrades: Operational HWRF scripts have been modified to accommodate changes due to one-way hybrid GSI, optimum utilization of CCS resources, and cross-platform compatibility required for transitioning to WCOSS in the middle of the season. Operational HWRF will remain in the vertical structure and will be known as hwrf.v7.0.0 on CCS and hwrf.v7.1.0 on WCOSS.