Converter carimbo de data/hora VARCHAR em TIMESTAMP?

SELECT STR_TO_DATE("17:16:28 Sep 13, 2011 PDT", '%H:%i:%s %b %d, %Y PDT');

EDITAR:

SELECT STR_TO_DATE(field_name, '%H:%i:%s %b %d, %Y PDT') AS new_time
FROM table_name;