According to the data, the rain mostly tapers off by the end of November in Nha Trang. Also Vinh Hy where Amanoi is located is pretty much of a micro-climate and gets much less rain than Nha Trang. According to the folks at Amanoi, there is almost no correlation between the weather there and the weather in Nha Trang. I had one afternoon with a couple of hours of rain while I was there, and it was actually a nice change. Also because the climate is so arid, I think the vegetation and look of the place improves when they get some rain.