When a vacancy occurs in the supreme court, the clerk of such court shall promptly notify the chairman of the commission of such vacancy, and the commission shall make nominations of three persons to fill such vacancy and certify the names of the nominees to the governor. When it is known that a vacancy will occur at a definite future date, but the vacancy has not yet occurred, the clerk shall notify the chairman of the commission thereof, and the commission may, within 60 days prior to the occurrence of such vacancy, make its nominations and submit to the governor the names of three persons nominated for such forthcoming vacancy. To the end that the administration of justice may be facilitated and that no vacancy on the supreme court may be permitted to exist unduly, the commission shall make its nominations for each vacancy and certify them to the governor as promptly as possible, and in any event not later than 60 days from the time such vacancy occurs.