def _masks_from_mask_at_t_location(tmask):
    """Return sea_binary_mask_at_[uvf]_location defined from
    sea_binary_mask_at_t_location.

    Parameters
    ----------
    tmask : xarray dataarray
        array of sea_binary_mask_at_t_location (mask==0 on land).
        assume that the order of the dimensions is ('y','x').

    Return
    ------
    masks : tuple of xarray dataarrays.
        umask refers to sea_binary_mask_at_u_location
        vmask refers to sea_binary_mask_at_v_location
        fmask refers to sea_binary_mask_at_f_location
    """
    umask = tmask  * tmask.shift(x=-1)
    vmask = tmask  * tmask.shift(y=-1)
    fmask = tmask \
              * tmask.shift(x=-1) \
              * tmask.shift(y=-1) \
              * tmask.shift(x=-1).shift(y=-1)
    return umask, vmask, fmask