November through February is peak season for excellent reason. Daytime temps sit at 25-28°C, humidity is tolerable, and rainfall is nearly zero. The sea is calm enough for safe swimming, jellyfish are absent, and visibility for snorkeling improves slightly. December and January are the busiest months; hotel rates double and beaches get crowded on weekends. Book accommodation six weeks in advance. November and February are shoulder within the peak season: 20% cheaper, fewer people, same weather.
Festivals cluster in this window. Eid-ul-Adha sometimes falls in late November or December (dates shift yearly), bringing domestic crowds but also night markets and food stalls worth experiencing. The Cox's Bazar Beach Festival runs for three days in late December with kite flying, sand sculpture, and concerts. If you hate crowds, avoid December 20-January 10 entirely.
June through September is monsoon season: heavy rain daily, rough seas, jellyfish blooms, and most outdoor activities canceled. Hotel rates drop 50% but it is a false bargain because you will spend all day indoors. Flooding is common in July and August. Do not visit unless you have no other option. March through May is the hot season: 35°C+ with brutal humidity. The beaches are usable early morning and late afternoon, but midday is unbearable. Rates are low, crowds are minimal, and if you can handle the heat it is actually a decent budget window.
October is the transition month. Early October still has monsoon tail-end rain. Late October is dry and pleasant but prices have not yet spiked. If you can travel October 20-31, you get near-peak weather at shoulder prices. April is similarly transitional: very hot but the Pohela Boishakh Bengali New Year festival on April 14 brings music, processions, and special menus at restaurants.
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