The -new_grid_winds option selects the wind rotation/orientation for the -new_grid option. Most users will want the winds to be oriented to the earth's north and south directions. This is done by using the -new_grid_winds earth option. Many of NCEP grids have the winds being rotated so that north direction is relative to the grid; i.e., grid point (i,j) to (i,j+1). For lat-lon, Mercator and Gaussian grids, the grid and earth relative directions are the same. For the Lambert conformal, polar stereographic and various rotated grids, the directions are different.