Obtain NAM Winds for ADCIRC

Special thanks to Shoshi Reich for providing the scripts to convert from grb to fort.22 format.

The North American Mesoscale (NAM) Forecast System is a regional weather model used to predict weather conditions across North America. It provides detailed forecasts for various weather parameters, including wind speed and direction, at different horizontal resolutions. The NAM model is particularly useful for short-range weather predictions, typically covering a period from 12 to 72 hours¹².

This is a short tutorial on the best way to obtain NAM data and convert it into a format ADCIRC can ingest.

 Instructions

Obtaining the data

1. Visit North American Mesoscale (NAM) Forecast System | National Centers for Environmental Information (NCEI)

2. Determine what kind of product you need, future (NAM Forecasts) or historical (NAM reanalysis) wind data

3. Option 1: Downloading via batch. This is probably the easiest path for most people.

   1. Under ‘Data Access Links’ select ‘AIRS’. You should see the following portal:

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   2. Select the sampling frequency under 'Select UTC Cycle (Hour). There is 6,12, and 18 hourly options. Also select the start and end time.

   3. The data is given in a time interval. Select ‘Yes’ under ‘Submit Batch’ if you want all the data for the entire time interval, otherwise you can select specific timestamps in the next screen.

   4. Enter your email address and ‘Proceed with Order’. You should receive an email that looks like:

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   5. The ‘Web Download’ link will take you to an archive with your files. You can use these links as a target for wget on TACC systems to download the tar files directly to TACC. Alternatively, you can use the ‘FTP (File Transfer Protocol) Download’ link if you want to get fancy.

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Converting data to ADCIRC format

1. Convert GRB files to NetCDF:

   • Decompress the tar files. You will get a kajillion grb2 files.

   • Ensure the netcdf, nco, and ncl_ncarg modules are loaded.

   • Convert the files with the command:

     ncl_convert2nc *.grb

2. Process NetCDF files:

   • You should now have a bunch of nam_*.nc files.

   • Use the script to:

     • Select the wind and pressure fields from all the NetCDF files.

     • Combine all the files into one NetCDF file called 10m_uvp_all.nc.

3. Create ADCIRC input files:

   • Use the 10m_uvp_all.nc file to create the fort.221 and fort.223 input files for ADCIRC:

     • Use for fort.221.

     • Use for fort.223.

   • Ensure to change the start date in the variable tbeg (on line 69).

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