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 FY2020 implementation:

  1. HWRF Infrastructure Enhancements:
    • The NMM core of the operational HWRF model is upgraded to latest community version referred to as V4.0a.
    • Use high-resolution land-sea masks for nested grid domains.
    • Use three-hourly boundary conditions from the GFS model, instead of six-hourly boundary conditions.
    • Optimize and unify domain sizes for initialization and data assimilation.
    • Adjust the horizontal mixing length scale for D03.
  2. HWRF Vortex Initialization and Data Assimilation Improvements:
    • Adopt new settings for Data Assimilation (DA) and Grid-pointImplemented stochastic physics for HWRF based DA system.
    • Turn off smoothing in Vortex Initialization (VI) and turn off intensity correction when model mean sea level pressure is shallower than observed and wind speed is stronger than observed.
    • Skip the effects of VI for weak storms with maximum speeds of 25 knots. Use GFS analysis for initial conditions for weak storms with maximum speed of less than 20 knots.
    • Implement a new domain merge method and procedure to handle the transition from HWRF to GFS analysis.
    • Update and fix issues related to preprocessing of temperature dropsonde data.
    • Upgraded data assimilation includes additional satellite observations and turning off thinned ASCAT data.
    • Assimilate the Next Generation Weather Radar (NEXRAD) radial wind data from coastal radar sites. This was a collaborative effort with AOML/Hurricane Research Division and Oklahoma University.
  3. HWRF Physics Advancements:
    • Use exponential random cloud overlap method with a constant decorrelation length in the RRTMG radiation scheme and include bug fix related to shortwave radiation.
    • Sync the scale-aware SAS convection scheme with a recent GFS version, but use HWRF detrainment rate.
    • Use the unified F-A microphysics scheme with bug fixes included.
  4. HWRF Air-Sea Interaction and Coupling Upgrades:
    • Use Global Real-Time Ocean Forecast System (RTOFS) to initialize the ocean model for the NATL basin.
    • Improve regridding of initial data from RTOFS to Princeton Ocean Model (POM) grid over shallow layers to fix cold spots of sea surface temperature.
    • Unify POM related scripts to support current and basin scale HWRF configurations.
    • Use a newer version of HYbrid Coordinate Ocean Model (HYCOM) for ocean coupling for the JTWC basins.
  5. HWRF Post-Processing and Product Upgrades:
    • Use an updated version of UPP.
    • Use the latest version of GFDL tracker.