Try to add this line:
missing_value=-1.E+30
to name=SM000010, SM010200, ST000010, and ST010200 in the METGRID.TBL, so that they look something like this:
name=SM000010
interp_option=sixteen_pt+four_pt+average_4pt+search
masked=water
interp_mask=LANDSEA(0)
fill_missing=1.
missing_value=-1.E+30
flag_in_output=FLAG_SM000010
Re-run metgrid.exe and see if that corrects the problem.
missing_value=-1.E+30
to name=SM000010, SM010200, ST000010, and ST010200 in the METGRID.TBL, so that they look something like this:
name=SM000010
interp_option=sixteen_pt+four_pt+average_4pt+search
masked=water
interp_mask=LANDSEA(0)
fill_missing=1.
missing_value=-1.E+30
flag_in_output=FLAG_SM000010
Re-run metgrid.exe and see if that corrects the problem.