NOUS41 KWBC 291418



Technical Implementation Notice 14-20

National Weather Service Headquarters Washington DC

730 AM EDT Tue Apr 29 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:  GFDL Hurricane Prediction System Changes:   

          Effective June 10, 2014


On or about Tuesday, June 10, 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, Cd)

- 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 basin

- 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 AWIPS.


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: