Joe,
the gribtonc decoder doesn't work with GRIB2 files. There is a decoder package GRIB java decoders at http://www.unidata.ucar.edu/software/decoders/ that manipulates the GRIB 2 files because most of the GRIB2 files are large. There is documentation on the web page with details. If you want to the completely decode a GRIB2 file, one would have to install the netCDF Java package and use routine.
java -Xmx512m -classpath $CP ucar.nc2.iosp.grib.Grib2Netcdf $INPUT $NC
There is a referance to netCDF Java on the page also.
robb...
