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Numerical Forecast Systems

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 2014 implementation include the following:

1. HWRF Infrastructure/Resolution Upgrades : The NMM core of the operational HWRF model will be upgraded to latest community version referred to as V3.6a. Due to computational constraints, FY13 HWRF was run with a coarse vertical resolution of 42 levels with model top extending only up to 50 hPa. Proposed FY14 HWRF will have vertical resolution increased to 61 levels with model top extending up to 2 hPa. This will allow the model to have the much desired higher resolution in PBL, and resolve the upper atmosphere more accurately. Extending the model top to 2 hPa will allow the HWRF Data Assimilation System to ingest more satellite radiance data which usually peaks above 50 hPa. The nest domain sizes will be increased by 20% for the 9km domain and by 10% for the 3km domain to allow the high-resolution nests capture larger storm regions within the moving domains.


2. HWRF Physics Upgrades : HWRF physics will undergo major upgrades which include RRTM-G for radiation, modified Ferrier Microphysics with advection of individual hydrometeors and an advanced land surface model (NOAH LSM). Radiation upgrades will improve the cloud-radiation interactions with better representation of cloud top cooling and cloud base warming. The proposed microphysics upgrades will enhance representation of the storm structure and provide more realistic distribution of hydrometeors, especially ice concentration and fall speeds. For the first time, a 4-level NOAH land surface model will be introduced into HWRF as a replacement of the GFDL slab model. NOAH LSM upgrades will address the cold land surface temperature bias noted in the current HWRF model forecasts, and will also provide the required surface runoff and base flow variables for landfall related downstream applications of river routing model and hydrology models.


3. HWRF Initialization Upgrades : Vortex initialization is modified with further improvements to the storm size correction and resizing the filter domain, and will better align the filtered vortex and the environment. For the first time, we will be continuously cycling the vortex from unnamed depressions (invests) when they transition into numbered/named storms, eliminating the cold starts for tropical storms.


4. HWRF Data Assimilation System (HDAS) Upgrades : The 80-member global ensembles based one-way hybrid EnKF-3DVAR data assimilation system for HWRF will further be upgraded to include more satellite data sets and aircraft recon data sets along with the NOAA-P3 Tail Doppler Radar data. The GSI system will be further tuned to improve the initial analysis for all HWRF domains.


5. HWRF Ocean Upgrades : Ocean model component of HWRF will be upgraded to multi-processor MPI-POM-TC with single trans-Atlantic domain and for the first time, a 3D ocean for Eastern Pacific basin instead of the current 1-D POM. The ocean model resolution will increase from 1/6o to 1/12o and will have a modified feature based initialization suitable for the MPI POM-TC model.


6. HWRF Coupler Upgrade : The single processor NCEP coupler in HWRF model will be upgraded to run on multiple processors to enable faster communications between the atmosphere and ocean components. This is required due to increased resolution


7. HWRF Post-Processing and Product Upgrades : HWRF post processing upgrades will include additional simulated synthetic imagery from different satellite sensors, and will have new products requested by SPC (tornadic potential fields) and for downstream applications including Hurricane Wave Model. For the first time, FY14 operational HWRF will now have complete GRIB2 support, eliminating all GRIB1 products from operational suite.


8. HWRF Script Enhancements and Procedural Upgrades : Operational HWRF scripts will undergo major enhancements with better exception handling features and efficiency. The new python based scripts will eliminate lot of duplication and will greatly reduce the length of HWRF scripts in operations. They also provide for the first time the opportunity to unify various versions of the scripts used by the community and developers. They also have the flexibility to add features that can be utilized for graphics and automation. Operational HWRF will remain in the vertical structure and will be known as hwrf.v8.0.0 on WCOSS.