Going by the height given, and appearance of the flower, there's a possibility that it could be Crinum moorei.
Crinum moorei has an interesting growth cycle here, where the foliage languishes during the heat of the late summer for a short time, then new leaves appear with the fall rains, followed by, or sometimes concurrent with, blooming stems. (Are they properly called scapes in Crinum?) I have several plants of moorei, one of which was passed along by a certified "Master Gardener" with a tag which said "Naked Lady" (a common name for Amaryllis belladonna, which it is obviously not.)
One distinguishing characteristic of moorei is the leaf, which is generally upright, but then relaxes mid-length. It's also keeled, with a prominent midrib when viewed from the underside. It can also exhibit a subtle pattern or texture of "netting". The powelii types have a broad, U-profile leaf, which is long, smooth, and recurves to the ground. Here, these tend to bloom in the spring-summer.
Ken
