NOUS41 KWBC 181400 AAB



Service Change Notice 17-84 Updated

National Weather Service Headquarters Silver Spring MD

1000 AM EDT Mon Sep 18 2017


To:      Subscribers:

         -NOAA Weather Wire Service

         -Emergency Managers Weather Information Network


         Other NWS Partners, Users and Employees


From:    David Myrick

         Office of Science and Technology Integration


Subject: Updated:  The Nearshore Wave Prediction System (NWPS)

         Upgrade v1.2 will be provided over the Satellite

         Broadcast Network (SBN) and NOAAPORT on or about

         November 14, 2017


Updated to add extra detail about the grids and to put in

standard wording to make sure users' decoders can handle any

grib2 changes.


Effective on or about Tuesday, November 14, 2017, additional

NWPS data will be added to the SBN and NOAAPORT. The NWPS is run

2-4 times per day, on-demand, depending on the coastal Weather

Forecast Office (WFO). On or about November 14, 2017, data will

increase to 144 hours (from 102 hours) with an increased

frequency to 1 hour (from 3 hours). This upgrade also features

the transition from regular model grids to unstructured

computational meshes for 10 WFOs (TBW, MFL, SJU, MHX, AKQ, OKX,

BOX, CAR, SGX, HFO) for improved nearshore accuracy; however,

the results from these unstructured meshes are interpolated onto

the existing regular grids for dissemination. These 1-hourly

grids will be disseminated in GRIB2 format. Grid resolutions

will be dependent upon individual coastal WFO.


The parameters associated with the messages at these 

resolutions are:


Q - Wind speed

R - Wind direction

Z - Current speed

Z - Current direction

Z - Water level

C - Wave height

D - Water depth

J - Peak frequency/period

K - Peak direction

Z - Wave length

O - Wave height of swell waves

O - Partitioned swell wave height

Y - Partitioned swell peak period

P - Partitioned swell mean direction


Z - Water level is the level relative to mean sea level (MSL,


D - Water depth is the vertical distance from the water

free surface and the seabed topobathy (meters).


Data volume will vary, depending on coastal WFO. The average

total data volume (all coastal WFOs) is approximately 16.6 GB

per day, with a peak load of 2.3 GB per hour.


The following summarizes the generic WMO Headers for the NWPS

data: T1T2A1A2iiCCCC, where:


T1 = E


T2 specifies the parameters (stated above)


A1 = A for CG0 grid; B for CG1 grid; C for CG2 grid; D for CG3

grid; E for CG4 grid, and F for CG5 grid


A2 specifies forecast hours: A=00; B=01,02,03; C=04,05,06;

D=07,08,09; E=10,11,12; F=13,14,15; G=16,17,18; H=19,20,21;

I=22,23,24,...,27; J=28,29,30,...,33; K=34,35,36,...,39;

L=40,41,42,...,45; M=46,47,48,...,51; X=52,53,54,...,57;

N=58,59,60,...,63; Y=64,65,66,...,69; O=70,71,72...,81;

P=82,83,84,...,93; Q=94,95,96,...,105; R=106,107,...,117;

S=118,119,...,129; T=130,131,...,141; U=142,143,144


ii = 88 (specifies surface)


For the 30 CONUS offices, CCCC corresponds to K, appended by the

3-letter AWIPS code. For OCONUS offices, CCCC corresponds to P,

appended by the 3-letter AWIPS code for the generating the 

6 coastal WFO domains, e.g.,:


HFO - Honolulu, Hawaii

GUM - Tiyan, Guam

AJK - Juneau, Alaska

AER - Anchorage, Alaska

ALU - Anchorage (Aleutian Islands), Alaska

AFG - Fairbanks, Alaska


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





In addition to NOAAPORT, data will be available through the NCEP

ftp/http services:


On implementation day the data for the new domains will be

available at:




The file format is the following:


For each of the 2-character regional codes (sr, er, wr, pr, ar)

the GRIB2 files are listed under date YYYYMMDD where YYYMMDD is

year, month, and day, 3-character WFO code (listed above, in

lower case), run cycle (CC) and model domain (CG = CG1, CG2,

CG3, CG4, CG5; or CG0). The run cycle always corresponds to the

analysis time of the run (HH). All output variables pertaining

to the run domain are stored in a single GRIB2 file. Note that

since the runs are on demand, not all CC cycles will be produced

during a given YYYYMMDD.






Inclusion of GFS fail-over:


To improve the overall robustness of NWPS, a fail-over to Global

Forecast System (GFS) wind input has been included in case of

incomplete or erroneous GFE wind input being received from a

WFO. When the Graphical Forecast Editor (GFE) wind input file

from a particular WFO is either: (a) absent, (b) incomplete

(less than 144 h of data), or (c) spurious (contains values in

excess of 199 knots), a fail-over to GFS wind input will be

invoked. Normal operation will resume again as soon as a correct

GFE wind file is received.


The NWPS website is located at:


For additional information regarding GRIB2 files, visit:


For questions pertaining to NWPS data, please contact:


Dennis Atkinson

NWS OSTI Marine Program Lead

NOAA/NWS/Office of Science and Technology Integration

Silver Spring, MD 20910


For questions regarding the model, please contact:


Michael Farrar

NCEP/Director, Environmental Modeling Center

College Park, MD 20746



For questions regarding data flow aspects, please contact:


Carissa Klemmer

NCEP/NCO Dataflow Team

College Park, MD 20746



National Service Change Notices are online at: