Take a look at this: www.weatherbase.com check on each city you plan to visit.

VN is a long country and is impacted by several different monsoon systems. November is the time the central area (Hoi, Hue, DaNang) gets deluged. There is annual flooding at this time of the year, and two out of three years there are deaths due to flooding in this area. You might want to re-consider your itinerary.

I spent 3 1/2 weeks last November in Vietnam, traveling from north to south. I'm not saying the weather this November will be the same as what we experienced, but here's an outline of what our weather was:

Nov. 2-4, Hanoi: sunny, cooler than we expected (still warm, though)
Nov. 4, Mai Chau: sunny with morning fog/mist
Nov. 5-8, Northwest (Son La, Dien Bien Phu, Lai Chau): warm, sunny, cool at night
Nov. 8-10, Sapa: cool rain and some gorgeous sun, glad we had rain jackets
Nov. 11-12, Halong Bay: perfect warm, sunny weather, full moon
Nov. 13-14, Hue: a bit of rain, mostly sunny and warm
Nov. 15-16, Hoian: mostly sunny, some rain at My Son
Nov. 16-17, Nha Trang: beautiful sunshine, windy, big waves, swam in a sheltered island cove
Nov 18-19, Dalat: sun and rain, cooler temps
Nov 19-20, Phan Thiet: sunny but windy
Nov. 20-24, HCMC and the Delta: sunny, hot, but comfortable

I would happily go again in November, but note that the week before we were in Hue/Hoian there was flooding in Hoian.