def _append_spc_date_to_storm_ids(primary_id_strings, spc_date_string):
    """Appends SPC date to each storm ID.

    N = number of storm objects

    :param primary_id_strings: length-N list of primary IDs.
    :param spc_date_string: SPC date (format "yyyymmdd").
    :return: primary_id_strings: Same as input but with new IDs.
    """

    return [
        '{0:s}-{1:s}'.format(p, spc_date_string) for p in primary_id_strings
    ]