Due to the size of the blossom, this is presently thought to be Zephyranthes rosea and not Zephyranthes grandiflora. Also referred to as Zephyr lily and rain lily. The later apparently due to its propensity for blooming after a rain.
See also:
http://www.zanthan.com/gardens/plants/zephyranthes1.html
http://www.flickr.com/photos/bcanna/47663316/
http://www.gaygardener.com/gardenspot/bulbs022.phtml
http://www.bulbsociety.org/GALLERY_OF_THE_WORLDS_BULBS/GRAPHICS/Zephyranthes/Zephyranthes_rosea/Z.rosea.html
http://davesgarden.com/guides/pf/go/1245/
Kingdom Plantae – Plants Subkingdom Tracheobionta – Vascular plants Superdivision Spermatophyta – Seed plants Division Magnoliophyta – Flowering plants Class Liliopsida – Monocotyledons Subclass Liliidae – Order Liliales – Family Liliaceae – Lily family Genus Zephyranthes Herbert – zephyr lily Species Zephyranthes rosea Lindl. – Cuban zephyr lily