When is the most humid time of the year in Vietnam?  

Vietnam has some very humid months, and high humidity throughout the year. The least humid month is December (74.1% relative humidity), and the most humid month is September (78.9%).

I believe December through February is the least humid period but you have to expect some humidity. It is much more humid than places like Japan. 

If you are not a fan of humidity, you will need to adjust. I can tell you that! My hair was not prepared for Vietnam! It doesn't matter what time of the year you go, it will be humid. 

If you went as a kid, you are very unlikely to remember what the weather felt like. Most days of the year, no matter the month will be humid or sticky. More so during the rainy season. 

It is humid all year round but the least humid times would be December until mid-February. At least this has been my experience. 

July, August, and September are especially humid so if you want to skip out on the humid weather, I would not book a trip in those months. As mentioned, December through February or March is a safe bet.

MoMo is not one I have ever heard of but it sounds very useful! I hate carrying cash on me when I am on a trip. I always tend to misplace it.