Pigeon Orchid

Dendrobium crumenatum, called Pigeon Orchid, Purse-Shaped Dendrobium, Bag-Shaped Dendrobium, of family Orchidaceae, subfamily Epidendroideae. It produces white, 5cm wide, fragrant flowers with a yellow tinted throat. The bloom cycle is triggered 9 days after a sudden drop in temperature (at least 5.5 °C or 10 °F), usually as a result of rain, although the same effect can be artificially created.

Dendrobium crumenatum flowers are fragrant, but only lasts for a day.
Pics #2-3 were taken a day before the blooms were out (pics #1, 4-6). The following day after blooming, the flowers withered already.