year/mm/dd hh:mm   BP       RH      AT     LWR     PRC     SST    SWR     WNDE    WNDN   SOG   COG    VANE
                   mb        %     DegC   W/m^2     mm     DegC  W/m^2     m/s     m/s    kt   deg    deg
2009/07/09 00:00 1013.32  57.115  26.635  384.4   -1.31  -5.000  997.5    1.14   -7.62  0.06 312.22  188.3

The AutoIMET system occasioally has a glitch which puts Na in place of the reading
They usually come in pairs, e.g. in the two wind fields or sog and cog
Frank Bradley cleans up by replacing with the previous values. His day files have
names of the form imetddd.txt where ddd is the Julian day number e.g. imet192.txt