1. gen_json.py (need PySCHISM nwm3.0 branch)
   inputs: nwm_v3 = '/sciclone/schism10/lcui01/schism20/ICOGS/ICOGS3D/Forecast/NWM/oper_3D/NWM_v3_final/NWM_v3_hydrofabric.gdb'
           hgrid

2. download.py 
    Because there is no Alaska data on either Google cloud or AWS yet, so I set up a crontab job to download data at 8AM everyday 
    from https://para.nomads.ncep.noaa.gov/pub/data/nccf/com/nwm/v3.0

3. link.py
    create a new folder cached/ and link *.nc files there. 
    change startdate, rnday, and basepath as needed.
    
4. gen_sourcesink.py
   generate source_sink.in, vsource.th, vsink.th, and msouce.th (temperature = -99999.0, salinity = 30 for this case)

   to run it: python gen_sourcesink.py YY-mm-dd (e.g., python gen_sourcesink.py 2023-05-02 for start_date 2023-05-02).