AP was right, I was at Mui Ne in January and had a great time, good wind most days for my 2 week stay. I believe there is wind July, August but more southerly, not as consistant either.It is the off season but you could be lucky.
Here's a link to a 7 day forecast, there may be other sites for the year's weather. Enjoy it now before the Ruskies take it over.
http://muinebeach.net/muineweather.htm 
