NOUS41 KWBC 081251



Service Change Notice 18-59

National Weather Service Headquarters Silver Spring MD

851 AM EDT Fri Jun 8 2018


To:       Subscribers: 

          -NOAA Weather Wire Service

          -Emergency Managers Weather Information Network


          -Other NWS Partners, Users and Employees


From:     Dave Myrick

          NWS Office of Science and Technology Integration


Subject:  Upgrade the Hurricanes in a Multi-scale

          Ocean-coupled Non-hydrostatic (HMON) Model:

          Effective July 9, 2018


Effective on or about Monday, July 9, 2018, beginning with the

1200 Coordinated Universal Time (UTC) run, the National Centers

for Environmental Prediction (NCEP) will upgrade the HMON

coupled (HMON-HYCOM) modeling system.


The scientific and technique enhancements include the following:


 - Upgrade of Non-hydrostatic Multi-scale Model on the B-grid

(NMMB) dynamic core with bug fixes

 - Model vertical resolution has been increased from 42 to 51


 - Improved vortex relocation

 - Updated convection scheme from Simplified Arakawa-Schubert

(SAS) scheme to scale-aware SAS scheme

 - Updated the Planetary Boundary Layer (PBL) scheme from the

Global Forecast System (GFS) PBL scheme to GFS Eddy-Diffusivity

Mass-Flux (EDMF) PBL scheme

 - Updated momentum and enthalpy exchange coefficients (Cd/Ch)

 - Added HYCOM coupling in the North Atlantic (NATL) basin

 - Unified HWRF/HMON coupler


The 2018 HMON system has been fully tested and compared with the

forecast skill of the 2017 operational HMON v1. Overall, it has

shown improved skill in track and intensity forecasts for both

NATL and Eastern Pacific (EPAC) basins.


Product Timing Changes:


Timing output will be up to 15 minutes later than the 2017 HMON

version for the NATL basin, and up to 5 minutes later for

Eastern and Central Pacific basins. All forecast products for

all basins will be available before T+6:00.


Sample HMON products from 2018 HMON are available at:


More details about the HMON system are available at:


NCEP encourages users to ensure their decoders are flexible and

are able to adequately handle changes in content order, changes

in the scaling factor component within the product definition

section (PDS) of the GRIB files, and any volume changes which

may be forthcoming. These elements may change with future NCEP

model implementations. NCEP will make every attempt to alert

users to these changes prior to any implementations.


Any questions, comments or requests regarding this

implementation should be directed to the contacts below. We will

review any feedback and decide whether to proceed.


For questions regarding these model changes, please contact:


  Dr. Avichal Mehra

  Lead Physical Scientist

  NOAA/NCEP/Environmental Modeling Center

  National Centers for Weather and Climate Prediction

  College Park, Maryland 



For questions regarding the data flow aspects of these data

sets, please contact:


   Carissa Klemmer

   NCEP/NCO Dataflow Team Lead

   College Park, MD



NWS Service Change Notices are online at: