Season desk
These are the usual windows. A dated field report, when one exists, replaces the guess on that place.
Rice and flowers
Northern mountain gold is often September to October. Tam Coc, near Ninh Binh, is often late May to early June. Ha Giang buckwheat is often October to November.
Floods and storms
The central coast, especially Hoi An, is most exposed from September to November. If a named storm is heading for Hue or Da Nang, treat boat trips and old-town nights as cancellable.
Tet
Lunar New Year moves. The week of Tet is the hardest week to travel. Flower markets in Hanoi and Ho Chi Minh City are the sight; closed shops are the cost.