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Technical Implementation Notice 14-20, Amended

National Weather Service Headquarters Washington DC

750 AM EDT Tue Jun 3 2014


To:       Subscribers:

          -Family of Services

          -NOAA Weather Wire Service

          -Emergency Managers Weather Information Network


          Other NWS Partners, Users and Employees


From:     Timothy McClung

          Science Plans Branch Chief

          Office of Science and Technology


Subject:  Amended: GFDL Hurricane Prediction System Changes:   

          Effective June 18, 2014


Amended to change the effective date from June 12 to June 18.  

If NWS declares a Critical Weather Day, this implementation may

be completed a day or two before or after the scheduled date.


On or about Wednesday, June 18, 2014, 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:


- Increased horizontal resolution of inner nest from 1/12th to

1/18th degree

- Improved specification of surface exchange coefficients (Ch,


- Improved specification of surface roughness and wetness over

land (climatology replaced by GFS based values)

- Modified PBL with variable Critical Richardson Number

- Improved targeting of initial storm maximum wind and storm

structure in initialization

- Advection of individual micro-physics species

- Removed vortex specification for storms of 40 knots and less

- Upgraded ocean model to about 9 km resolution MPI-POM with

unified trans-Atlantic basin and 3D ocean for Eastern Pacific


- Introduced direct interpolation from GFS hybrid to GFDL sigma



Extensive testing over multiple hurricane seasons show

significant improvements in prediction of storm intensity at all

forecast time levels in both the Atlantic and Eastern Pacific.

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

times in the Atlantic, with about 6 percent in the critical 1-2

day lead times. Reduced track error averaged 6 percent in the 1-4

day lead times and neutral at Day 5.  The excessive over-

intensity bias of the GFDL model for weak systems was greatly

reduced, increasing the reliability of the model as an intensity

guidance tool.


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



There are no changes to existing output content.  These changes

will result in no change in product dissemination time, or

increase in product size.


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 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.


For questions regarding these model changes, please contact:


Morris Bender


Princeton, NJ

Phone: 609-452-6559


Timothy Marchok


Princeton, NJ

Phone: 609-452-6534


NWS National Technical Implementation Notices are online at: