Hoi An in December

February through May delivers perfect weather - warm days, cool evenings, minimal rain. March and April hit the sweet spot with temperatures around 75-80°F and clear skies for cycling. Monsoon season (September-January) brings flooding that can shut down the Ancient Town for days. The Thu Bon River rises fast and streets become canals. But room rates drop 40% and you'll have temples mostly to yourself. Lantern Festival happens monthly on the 14th day of the lunar calendar. The entire Ancient Town goes dark except for silk lanterns and candles. Cars get banned, locals dress in traditional ao dai, and the atmosphere turns magical. Check lunar calendars and book ahead. Tet (Vietnamese New Year) in late January or February brings family reunions and closed shops. The town empties of tourists but fills with returning locals. It's cultural immersion or total shutdown, depending on your perspective. Summer (June-August) means 90°F heat and afternoon thunderstorms. Morning temple visits work fine, but save afternoon activities for air-conditioned tailor shops or beach time at An Bang.