Weather
Dry, sunny and 25–31°C almost everywhere. The Andaman is at its calmest; the Gulf can still see rain in the first half, so Samui is better after mid-month.
The north gets genuinely cool at night — 15°C in Chiang Mai is normal, and hill towns drop below 10°C.
The Christmas squeeze
From 20 December to 5 January prices roughly double and the good hotels sell out. If you want that window, book by September; if you can move, the first two weeks of December are excellent value.
What to do
Beach first, cities second — Bangkok is pleasant when the heat breaks. Book boats early; the good operators are full every day between Christmas and New Year.
