def _monyearstrings(mon, year, mon_dict, meteoyearfunc):
    """
    Increment the months and potentially the years.

    Assemble the strings that will allow ``_meteofinder`` to get correct files.

    Parameters
    ----------
    mon : int
        Integer representation of the month
    year : int
        Integer representation of the year
    mon_dict : dictionary
        Dictionary keyed by month integer, with lists of [season, mon]
    meteoyearfunc : function
        Function that formats the year string to length 2 or 4 to identify
        appropriate meteorology files

    Returns
    -------
    prv : string
        Signature for gathering the meteorology files for the previous month
    nxt : string
        Signature for gathering the meteorology files for the next month
    now : string
        Signature for gathering the meteorology files for the current month

    """
    next_year = year
    prev_year = year

    next_mon = mon + 1
    prev_mon = mon - 1

    if prev_mon == 0:
        prev_mon = 12
        prev_year = year - 1
    if next_mon == 13:
        next_mon = 1
        next_year = year + 1

    w = '*'

    prv = w + mon_dict[prev_mon][1] + w + meteoyearfunc(prev_year) + w
    nxt = w + mon_dict[next_mon][1] + w + meteoyearfunc(next_year) + w
    now = w + mon_dict[mon][1] + w + meteoyearfunc(year) + w

    return prv, nxt, now