Except for possibly using an iCalendar kludge (see other google-calendar questions about unusual repeating events) there does not appear to be a way to do it with the Google Calendar interface.
"Daily" repeating events only let you choose up to 30 day intervals. Similarly, "Weekly" only lets you choose an interval of up to 30 weeks.
"Monthly" won't work, because even if you choose a 12-month interval, you still have to choose a day of the month (13th) or a day of the week (second Friday). And, of course, "Yearly" only lets you choose a specific date.
I think the best you'll be able to do is to make a Yearly event on September 13, and then manually move those occurrences in leap years back the the 12th.