NOUS41 KWBC 021450



Technical Implementation Notice 14-22

National Weather Service Headquarters Washington DC

1050 AM EDT Fri May 2 2014


To:†††††† Subscribers:

††††††††† -Family of Services

††††††††† -NOAA Weather Wire Service

††††† ††††-Emergency Managers Weather Information Network

††††††††† -NOAAPORT

††††††††† Other NWS Partners, Users and Employees

From:†††† Tim McClung

††††††††† Science Plans Branch Chief

††††††††† Office of Science and Technology

Subject:Change to Global Wave Ensemble System

††††††††† Effective June 17, 2014


On or about Tuesday, June 17, 2014, beginning with the 1200

Coordinated Universal Time (UTC) cycle, the National Centers for

Environmental Prediction (NCEP) will introduce several major

upgrades to its Global Wave Ensemble System. These changes will

affect the quality of output products, the spatial grid of output

products, the naming of the system and output files, and

introduce new products. The key changes for the Global Wave

Ensemble System are as follows:


1. Name change


The system will no longer be identified by the acronym MENS

(Multi-wave ENsemble System). It will now use the new acronym

GWES (Global Wave Ensemble System). This will impact output file

names as described below.


2. Wave Evolution Physics

- new physics package for wave growth under wind seas

- new physics package to account for swell dissipation for

swells propagating long distances.

- new physics package for wave dissipation due to wave



The new physics packages are outlined in Ardhuin et al., 2010.

Previous upgrades made to NCEPís wave forecasting systems

GLW/GLWN and MULTI1 have shown that the new physics significantly

improve model skill for wave height, especially in regions of

strong storm wind forcing. This will reflect in crucial

improvement in forecast performance for extreme wave prediction,

an important feature considering the widespread usage of NCEPís

wave ensemble system by the National Hurricane Center (NHC).


3. Spatial resolution change


The upgrade will increase the spatial resolution from a regular

1 x 1 degree global domain, to a 0.5 x 0.5 degree global grid.


4. Output products changes


4.1. File name changes


The change in the acronym used to identify the system will result

in changes to the names of output files. These files will also

become larger files because sizes are affected by the spatial

resolution increase. Gridded output will also include new

parameters representing spectral partitions, which will provide

users a more accurate description of wave systems. This change

will bring the wave ensemble system to the current state of other

wave models in terms of type and number of output parameters in

gridded output files. In most cases, the effect on the filename

is that "mens" is changed to "gwes" in the filename.The webpage


outlines the current files available and shows the new filenames

for these products.


4.2 Change to spectral output files


The spectral output files for the individual members and the

ensemble products will now be compressed. Output filenames will

end in "gz," with an example gwes00.t00z.spec_tar.gz.


4.3 Location change of output files


With this implementation, the location of the output data on the

ftp servers will be changed. Data are currently available in a

general directory named "wave".With this implementation, the

GWES data will be put in a directory named "gwes."The full

directory paths are listed below.


The output data from these models will be disseminated on the

NCEP server at:



and on NOMADS at:


where YYYYMMDD is the 4-digit year, month and day.



Sample output files from the new physics are available at:

A consistent parallel feed of data will be available on the NCEP

server once the model is running in parallel in early May. The

parallel data will be available via the following URLs:

NCEP urges all users to ensure their decoders can handle changes

in content order, changes in the scaling factor component within

the product definition section (PDS) of the GRIB files, changes

to the GRIB Bit Map Section (BMS), and volume changes. These

elements may change with future NCEP model implementations. NCEP

will make every attempt to alert users to these changes before



For questions regarding these model changes, please contact:


Henrique Alves

NCEP/Marine Modeling and Analysis Branch

College Park, Maryland


For questions regarding the dataflow aspects of these data sets,

please contact:


Rebecca Cosgrove

NWS/NCEP Central Operations

College Park, MD


NWS Technical Implementation Notices are online at: