NOUS41 KWBC 111847 AAA


Technical Implementation Notice 12-18, Amended

National Weather Service Headquarters Washington DC

248 PM EDT Fri May 11 2012


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 May 29, 2012


Amended to reschedule the implementation for Tuesday, May 29, 2012.


Effective on or about Tuesday, May 29, 2012, 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:


- Bug fix in PBL scheme from 2003 implementation

- Bug fix in Simplified Arakawa-Schubert (SAS) deep convection

  from 2010 implementation

- Implementation of GFS Shallow Convection

- Modification of the surface exchange coefficient (ch, cd)

- Modifications to GFS PBL scheme and momentum mixing term in    

  SAS deep convection

- Detrained micro-physics generated in SAS and passed to

  Ferrier micro-physics scheme

- Reduced specification of storm size for larger storms


In tests of storms from the 2011 Atlantic hurricane season, these improvements resulted in an average reduction of track forecast error of about 12 percent in the 2 to 5 day forecast time periods.


The average reduction in intensity errors averaged nearly 20 percent in the Atlantic basin during the same forecast time periods for the 2011 Atlantic hurricane season, primarily through elimination of the large positive intensity bias.


Product Changes:


The GFDL hurricane model GRIB products are disseminated via the NCEP and NWS FTP servers and are not available on NOAAPORT or AWIPS. These changes will result in no change in product content or dissemination time.  


The GFDL data is available on the NWS ftp server at:

where xx is the model cycle,


and at the NCEP servers at:




where YYYY is year, MM is month, DD is day, and HH is model cycle.


More details about the GFDL hurricane prediction system are online 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: