NCEP/EMC HWRF for Global TCs

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The HWRF group at EMC works in conjunction with members of the Global, Mesoscale, and Marine branches to continually make improvements to the Hurricane Weather Research and Forecast (HWRF) modeling system 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. This system is developed and supported by the Environmental Modeling Center (EMC) and operated by NCEP Central Operations (NCO) since 2007. HWRF consists of multiple movable two-way interactive nested grids that follow the projected path of the storm. Atmospheric component of the HWRF model was coupled to the Princeton Ocean Model (POM) developed by GFDL/URI using a sophisticated coupler developed at NCEP for providing accurate representation of air-sea interactions. An advanced vortex initialization scheme and NCEP GSI based HWRF Data Assimilation System (HDAS) provide means to represent the initial location, intensity, size and structure of the inner core of a hurricane and it’s large-scale environment. The NCEP Global Forecast System (GFS) analysis and forecasts provide initial and boundary conditions for the HWRF model. POM uses a feature based initialization procedure for representing oceanic features such as the loop current, warm/cold core rings and the cold wake generated by the storm.

HWRF team at EMC has also been providing experimental real-time forecast guidance for all tropical cyclone basins in the world (including Western North Pacific, Southern Pacific, North Indian and South Indian Ocean regions) to the Joint Typhoon Warning Center (JTWC) and National Weather Service (NWS) Pacific Region (PR) with support from NOAA’s Hurricane Forecast Improvement Project (HFIP) and using HFIP Research&Development computational resources on Jet supercomputers. Based on the demonstration of superior performance from HWRF compared to other regional models, JTWC has included HWRF model guidance in their operational consensus forecasts.

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.

Highlights for HWRF's FY2017 implementation:

  1. HWRF Infrastructure Enhancements:
    The NMM core of the operational HWRF model is upgraded to latest community version referred to as V3.8.1. Increase model vertical resolution from L61 (model top 2mb) to L75 (model top 10mb) for North Atlantic (NATL), Eastern Pacific (EPAC), and Central Pacific (CPAC) basins, and from L43 (model top 50mb) to L61 (model top 10mb) for Western Pacific (WPAC) and North Indian Ocean (NIO) basins. Meanwhile, slightly reduce the sizes of the two nested domains, from 25 x 25 deg to ~24 x 24 deg for domain 2 and from 8.3 x 8.3 deg to ~7.0 x 7.0 deg for domain 3. And consider storm’s meridional movement when determining parent domain center. Besides, a new version of Geophysical Fluid Dynamics Laboratory (GFDL) vortex tracker is implemented.
  2. HWRF Physics Advancements:
    • Updated scale-aware SAS convection scheme
    • Updated Ferrier-Aligo microphysics scheme
    • Partial cloudiness modification for RRTMG radiation scheme
    • Updated air-sea momentum and enthalpy exchange coefficients
  3. HWRF Vortex Initialization and Data Assimilation Improvements:
    • Improved vortex initialization with use of a new composite storm vortex
    • Upgrades to Grid-point Statistical Interpolation (GSI) including new data sets for GSI (e.g., hourly shortwave, clear air water vapor and visible AMV’s from GOES, HDOBS flight level data)
    • Inclusion of fully cycled HWRF ensemble hybrid Data Assimilation System for Tail Doppler Radar (TDR) and priority storms
    • Increasing the blending threshold of vortex initialization (VI) and GSI analysis (from 50 to 65 kt)
  4. HWRF Air-Sea Interaction and Coupling Upgrades:
    • Reducing coupling time step from 9 min to 6 min for both ocean and wave coupling
    • Increasing vertical levels for MPIPOM-TC ocean model from 23 to 40 levels
    • Introducing Hybrid Coordinates Ocean Model (HYCOM) coupling for WPAC and NIO basins.
    • Enabling one-way coupling to wave model (Wave Watch III) for CPAC, in addition to NATL and EPAC basins.
    • Obtaining waves boundary conditions from the NCEP global wave model (Multi_1)
    • Using ROTFS data to initialize MPIPOM-TC ocean model for CPAC storms, in addition to EPAC storms
  5. HWRF Post-Processing and Product Upgrades:
    New hurricane surface wave products are included for the NATL, EPAC, and CPAC basins, which allows decommissioning of the NCEP operational Hurricane Wave model (Multi_2). Besides, maximum number of storms can be run in operational increases from 7 to 8 storms.