NOUS41 KWBC 111730

PNSWSH

 

Technical Implementation Notice 15-26

National Weather Service Headquarters Washington DC

330 PM EDT Mon May 11 2015

 

To:       Subscribers:

          -Family of Services

          -NOAA Weather Wire Service

          -Emergency Managers Weather Information Network

          -NOAAPORT

          Other NWS Partners, Users and Employees

 

From:     Timothy McClung

          Chief Operating Officer

          NWS Office of Science and Technology Integration

 

Subject:  GFDL Hurricane Prediction System Changes:   

          Effective June 9, 2015

 

Effective on or about Tuesday, June 9, 2015 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:

- Improved initialization of moisture field in the vortex

initialization

-Reintroduction of the vortex initialization for all forecasts

except Nameless systems

- New specification of storm size in the vortex initialization.

- Correct specification of ocean currents in the surface flux

computation

- Modification of criterion for large-scale condensation in the

free atmosphere

- Bug Fix in GFDL coupler

 

Extensive testing over multiple hurricane seasons shows

significant improvements in the prediction of storm intensity in

both the Atlantic and Eastern Pacific. Intensity errors decreased

about 10% in the 1-3 day lead times in both basins. Reductions in

track error averaged 5 percent in the 1-3 day lead times in the

Atlantic and about 10 percnet in the Eastern Pacific at days 4-5.

The excessive negative intensity bias of the GFDL model was

significantly reduced in both the Atlantic and Eastern Pacific,

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, but there are

changes to all of the GRIB file names to more clearly identify

the domain coverage of the files.  File name changes are as

follows:

 

The file ID for the GRIB file covering the full 75x75 degree

domain at 1-degree resolution will change from having the

character string ".grib." to having the string ".grib.1p00",

 

The file ID for the GRIB file covering the full 75x75 degree

domain at 1/6-degree resolution will change from having the

character string ".grib6th." to having the string ".grib.0p16",

 

The file ID for the GRIB file covering the inner-nest, 5x5 degree

domain at 1/18-degree resolution will change from having the

character string ".gribn3." to having the string ".grib.0p05".

 

For example:

 

      2014 GFDL                       2015 GFDL

 

*.YYYYMMDDHH.grib.fhh*    --> *.YYYYMMDDHH.grib.1p00.fhh*

 

*.YYYYMMDDHH.grib6th.fhh* --> *.YYYYMMDDHH.grib.0p16.fhh*

 

*.YYYYMMDDHH.gribn3.fhh*  --> *.YYYYMMDDHH.grib.0p05.fhh*

 

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

cycle, and hh is a 2 or 3-digit forecast hour (00, 06, 12, ...,

114, 120, 126), and * at the end of the file name designates

availability of .grib2 files.

 

These changes will result in no change in product dissemination

time, or increase in product size.

 

Please note that data from the GFDL model will continue to be

available in both grib1 and grib2 format for the 2015 season. 

However, the grib1 data will be discontinued for the 2016

hurricane season, so NCEP encourages users to transition to using

the grib2 data this season.

 

More details about the GFDL hurricane prediction system are

available at:

 

http://www.gfdl.noaa.gov/operational-hurricane-forecasting

 

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

GFDL/NOAA

Princeton, NJ

Phone: 609-452-6559

morris.bender@noaa.gov

 

Timothy Marchok

GFDL/NOAA

Princeton, NJ

Phone: 609-452-6534

timothy.marchok@noaa.gov

 

NWS National Technical Implementation Notices are online at:

 

http://www.nws.noaa.gov/os/notif.htm

 

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