Parallel HWRF Ensemble Forecast

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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 FY2015 implementation:

  1. HWRF Infrastructure/Resolution Upgrades : The NMM core of the operational HWRF model will be upgraded to latest community version referred to as V3.6.1. With the availability of additional computational resources on WCOSS Phase 2, atmospheric component of the HWRF model will be upgraded from 27/9/3 km resolution to a higher resolution operating at 18/6/2 km resolution. This will allow the model to better resolve the fine scales of hurricane inner core structure and provide improved intensity, size and structure forecasts.
  2. HWRF Physics Upgrades : HWRF physics will undergo major upgrades which include RRTM-G with parameterized subgrid-scale clouds for radiation, advanced Ferrier-Aligo Microphysics, improved PBL with wind-speed dependent vertical mixing coefficient, modified GFDL surface physics with improved specification of drag coefficient for momentum, 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. The PBL and surface physics upgrades are aimed at improved representation of hurricane surface and boundary layer structures at high wind 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, to be consistent with the increased resolution of both HWRF model and the parent model (GFS) that provides initial and boundary conditions.
  4. HWRF Data Assimilation System (HDAS) Upgrades : Upgrade to the latest EMC GSI v5.0.0, enlarge d2 (6km) and d3 (2km) analysis domains to address discontinuity in the initial condition  between forecast domains, and for the first time, assimilate the MSLP data from tcvitals along with dropsonde data from all available aircraft recon missions including NOAA P3, GIV, AF C-130 and Global Hawkand. For non-TDR cases, use the 80-member global ensemble based one-way hybrid EnKF-3DVAR 6h forecast fields to calculate the covariance; run GSI on d2 analysis domain and add analysis increment to d3; no satellite DA on d3 analysis domain due to pronounced negative impact. And for TDR cases, run 40-member HWRF ensembles for 6h to provide more accurate, flow-dependent, vortex-dependent data assimilation covariance; run GSI on both d2 and d3 analysis domains. The GSI system will be further tuned to improve the initial analysis for all HWRF domains.
  5. HWRF Post-Processing and Product Upgrades : HWRF post processing upgrades will include additional simulated synthetic imagery from different satellite sensors.
  6. HWRF Script Enhancements and Procedural Upgrades : Operational HWRF scripts will be converted to full python based scripts, following successful implementation of hybrid ksh-Python system implemented in 2014. Operational HWRF will remain in the vertical structure and will be known as hwrf.v9.0.0 on WCOSS.
  7. Expanding HWRF Model Guidance for all Global Tropical Ocean Basins : With support from NOAA HFIP and using dedicated HFIP computational resources, starting in 2012, HWRF team at EMC has been providing JTWC with experimental real-time forecasts for the WPAC basin. By January 2014, HWRF forecasts are extended to all global tropical oceanic basins (including NIO, SIO and SP). HWRF team at EMC is responsible for determining the priority and setting up the real-time model runs based on tcvitals provided by JTWC. Although graphical HWRF products are made available to JTWC through EMC HWRF web server, there is no mechanism for disseminating forecast products to the WFOs and to the public through official NCEP channels. Following recent requests from NWS Pacific Region and JTWC to make the experimental HWRF model runs operational for WPAC, NIO, SIO and SP basins; NCEP operational HWRF will be designed to provide real-time 126-hr HWRF forecasts four times a day, for a maximum of 7 storms covering all global tropical cyclones during their entire life cycle, and will be run throughout the year. (Previous capability is limited to a maximum of 5 storms in the ALT/EPAC basins).