May is still a great time to visit Vietnam especially when you can take advantage of the lower airfares and hotel prices. To make the most of your time you just have to make a few adjustments compared to travelling during the winter months.
The North is now getting very warm with Hanoi enjoying an average temperature of 29°C, which is great news if you plan to include a Halong Bay cruise or would like to hike in the hills around Sapa and Ha Giang, by which time their rice fields should be an emerald green. Alternatively head south of Hanoi to Cuc Phuong National Park and ribbons of butterflies should fill the skies.
If you’re planning to include a beach stay, Hoi An and Nha Trang offer the best conditions. Although the south coast (Mui Ne, Phan Thiet & Phu Quoc) is still primarily dry, humidity is rising ahead of the June rains. In Saigon you can enjoy weather in the high 20’s and any rain tends to be in the form of short, heavy afternoon downpours.