NOUS41 KWBC 091500



Technical Implementation Notice 16-17

National Weather Service Headquarters Washington DC

1100 AM EDT Thu Jun 9 2016


To:       Subscribers:

          -NOAA Weather Wire Service

          -Emergency Managers Weather Information Network


          Other NWS Partners, Users and Employees


From:     Timothy McClung

          Portfolio Manager

          NWS Office of Science and Technology Integration


Subject:  GFDL Hurricane Prediction System Changes:   

          Effective July 12, 2016


Effective on or about Tuesday, July 12, 201,6 beginning with the

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

for Environmental Prediction (NCEP) will upgrade the Geophysical

Fluid Dynamics Laboratory (GFDL) Hurricane Prediction System.


The scientific changes to the model include the following:


- Modified detrainment of micro-physics in the Simplified

  Arakawa-Schubert (SAS) convection scheme

- Modified convective time scale in calling of SAS convection.

- Bug Fixes in the SAS scheme

- Improved representation of the storm initial wind profile

- Changed Ocean Initialization to run with Real Time Ocean

  Forecast System (RTOFS) analysis in the Eastern Pacific

- Added new functionality to ingest Global Forecast System (GFS)

  GRIB data to create the lateral boundary condition.


Extensive testing over multiple hurricane seasons show

significant improvements in the prediction of storm track and

intensity in both the Atlantic and Eastern Pacific basins.

Reductions in track error averaged 25 percent in the 4-5 day

lead times in the Atlantic and about 17 percent  in the Eastern

Pacific at days 3-5.


Intensity errors decreased about 15 percent in the 3-5 days lead

times in the Atlantic. With better representation of the

hurricane-ocean interaction in the Eastern Pacific through the

introduction of the RTOFS analysis, the cooling in the cold

wakes will be significantly reduced, increasing the reliability

of the model to predict rapid intensity change events.


Impact to Output Products:


The GFDL hurricane model GRIB products are disseminated via the

NCEP and NWS FTP servers and are not available on NOAAPORT or



In NWS TIN 15-26


NWS announced that the GRIB1 output from the GFDL would be

discontinued in the 2016 hurricane season given that it had been

replaced by GRIB2.  Therefore, all GRIB1 output files will be

removed from our servers with this upgrade.  This means all the

files at,

(where xx = cycle) will be removed.


On the NCEP ftp server


and at NOMADS:

in directories hur.YYYYMMDDCC (where YYYYMMDDCC is the year,

month, day and cycle) only the files with *grib2 on the end and

*.stats.short will remain.


There are no changes to existing GRIB2 output content, however

forecast products will be available about 10 minutes earlier due

to the use of GRIB 2 data for the lateral boundary generation.


More details about the GFDL hurricane prediction system are

available at:


NCEP encourages all 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 also any volume

changes.  These elements may change with future NCEP model

implementations. NCEP will make every attempt to alert users to

these changes prior to any implementations.


For questions regarding these model changes, please contact:


Morris Bender


Princeton, NJ

Phone: 609-452-6559


Timothy Marchok


Princeton, NJ

Phone: 609-452-6534


For questions regarding the data flow aspects of these data

sets, please contact:


Carissa Klemmer

NCEP/NCO Dataflow Team Lead

College Park, MD



NWS National Technical Implementation Notices are online at: