NOUS41 KWBC 171445 AAA

PNSWSH

 

Technical Implementation Notice 14-40 Amended

National Weather Service Headquarters Washington DC

945 AM EST Mon Nov 17 2014

 

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, Science Plans Branch

         Office of Science and Technology

 

Subject: Amended: Changes to the Hurricane (multi_2) and the

         Global (multi_1) wave models Effective January 7, 2015

 

Amended to change effective date to Wednesday, January 7, 2015

 

Effective Wednesday, January 7, 2015, beginning with the 1200

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

Environmental Prediction (NCEP) will upgrade the Hurricane and

Global wave models to WAVEWATCH III v4.15.1 and update the

underlying grids.

 

The Hurricane wave model (multi_2) uses a blend of GFS winds and

hurricane winds at 10 m above Mean Sea Level (MSL) as forcing

conditions, while the Global wave model (multi_1) uses just the

GFS forcings and is run side by side with the GFS forcing. Both

models use the same set of grids with the exceptions that the

multi_2 system has two additional regional grids (for blended

hurricane winds) and the multi_1 system has an Arctic grid (not

needed for propagating hurricane driven winds). Also the multi_1

system provides wave guidance out to 180 hours while the multi_2

system only goes out to 126 hours, the extent of the hurricane

guidance. It is useful to think of multi_1 as an early guidance

and multi_2 as a late guidance that includes the effects of

hurricane wind forcings.

 

The implications of the changes are highlighted below.

 

HURRICANE WAVE MODEL (multi_2) :

1. The Hurricane Wave model has been upgraded to the new

physics package that the Global Wave model uses. With this

change, both the Global and Hurricane wave models now use

the same physics. The advantages of the new physics packages

are:

  a. Better swell dissipation characteristics (this has

     implications for storms in the Pacific that have a

      strong swell component)

  b. Better wave growth and decay properties as the storm

     passes

  c. A much better representation of the wave spectra,

     leading to a more accurate estimate of peak frequency

     and consequently storm arrival times

 

2. Update of the bathymetry of the various grids to be ETOPO1

based. ETOPO1 is a 1 arc-min global relief model of the

Earth that is provided by the National Geophysical Data

Center (http://www.ngdc.noaa.gov/mgg/global/global.html).

The bathymetry used to be based on the ETOPO2 bathymetric

set which was an earlier 2 arc-min global relief model.

3. Hurricane winds are now forced by the HWRF model as opposed

to the GFDL model.

4. Wave products are being delayed by an hour. Due to the

timing of the products the hurricane wave model was being

run using the previous cycle hurricane winds. Thus a 12Z

wave model would use 06Z hurricane winds. By delaying the

wave product delivery by an hour the 12Z cycle wave model

would use the 12Z cycle hurricane winds. Thus, the wave

products are actually being delivered earlier.

 

GLOBAL WAVE MODEL (multi_1):

1. The grids of the wave model are updated to be ETOPO1 based

(as opposed to ETOPO2 based)

2. The masks for the regional grids (wc_10m, at_10m and ep_10m)

are updated as per requests of Ocean Prediction Center and

Guam Weather Forecasting Office

3. There has been a change to a sub-section of output points

that were requested by the Ocean Prediction Center. They

have now requested a smaller set of output points. The list

of current and new points is listed here:

 

http://www.nco.ncep.noaa.gov/pmb/changes/wave_multi_bndry.shtml

 

The output data from these models are disseminated on the NCEP

server at

 

http://www.ftp.ncep.noaa.gov/data/nccf/com/wave/prod/

and

ftp://ftp.ncep.noaa.gov/pub/data/nccf/com/wave/prod/

 

Sample output files from the new physics are available at

 

ftp://polar.ncep.noaa.gov/pub/waves/develop/

 

Details about the NCEP Multi-grid Wave Model are online at:

 

http://polar.ncep.noaa.gov/waves/index2.shtml

 

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

server by mid October via the following URLs:

 

http://www.ftp.ncep.noaa.gov/data/nccf/com/wave/para

 

ftp://ftp.ncep.noaa.gov/pub/data/nccf/com/wave/para

 

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

implementation.

 

For questions regarding these model changes, please contact:

 

  Hendrik Tolman

  NCEP/Marine Modeling and Analysis Branch

  NCWCP

  College Park, Maryland

  301-683-3748

  hendrik.tolman@noaa.gov

 

For questions regarding the dataflow aspects of these data sets,

please contact:

 

  Justin Cooke

  NCEP/NCO Dataflow Team

  NCWCP

  College Park, Maryland 20746

  301-683-3833

  ncep.list.pmb-dataflow@noaa.gov

 

NWS National Technical Implementation Notices are online at:

 

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

 

$$