When To Go · Country Guide
Two seas, two seasons: build your Thailand trip around the coast that is in form
Updated Mar 4, 2026 • 10 sources
When To Go
Season planner for Thailand
Thailand is not a single-season destination. Plan around which coast is calmer, not just which month you are traveling. The Andaman Sea (Phuket, Krabi, Khao Lak, Koh Lanta, Koh Lipe) is most reliable in the drier window, while the Gulf of Thailand (Koh Tao, Samui, Phangan, Chumphon) often has its best run in different months. Use the tracks below to pick the right coast, then confirm park opening dates and local boat schedules.
At A Glance Heatmap
| Activity | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Overall | ||||||||||||
| Scuba | ||||||||||||
| Freedive | ||||||||||||
| Snorkel | ||||||||||||
| Topside |
Activity Drilldowns
OverallNovember - April (Andaman focus) & March - September (Gulf focus)·Crowd:Moderate·Cost:Midrange
Ideal: Drier weather overall, calmer seas on most routes, and comfortable travel days.
Plan Carefully: Transition month. Parts of the Andaman reopen mid-month in some years, while the Gulf can see rougher seas and heavier rain.
If your dates are fixed, choose the coast that matches the season rather than trying to force a specific island.
ScubaNovember - April (Andaman marine-park season) & March - September (Koh Tao consistency)·Crowd:High·Cost:Midrange
Ideal: Best mix of visibility and sea state. Andaman offshore trips run most reliably, and the Gulf is warm and active.
Plan Carefully: Reposition by coast. The Andaman may reopen later in the month, while the Gulf can be windy and rainy.
For the Similan and Surin circuit, confirm seasonal opening dates and any eticket requirements well before travel.
FreediveMarch - September (Gulf training season)·Crowd:Moderate·Cost:Budget
Ideal: Most consistent for repeat training days in the Gulf, with warm water and frequent departures.
Plan Carefully: Gulf sea state can be disruptive, and the Andaman is still in transition. Pick sheltered bays and keep plans flexible.
Thailand's national marine rules require supervision standards for snorkeling and freediving.
SnorkelDecember - April (Andaman clarity) & March - September (Koh Tao bays)·Crowd:High·Cost:Budget
Ideal: Better odds of calm surfaces and clear shallows, especially in sheltered bays and on earlier boat departures.
Plan Carefully: Higher chance of wind and rain interruptions. Keep itinerary flexible and avoid exposed snorkel sites when winds build.
Snorkeling is the activity most sensitive to surface chop.
TopsideNovember - February (cooler, drier travel) plus March - April for beach heat·Crowd:High·Cost:Midrange
Ideal: Comfortable daytime temperatures, lower humidity, and strong overall travel conditions.
Plan Carefully: Transition weather. Expect sudden storms and adjust boat-heavy days to calmer windows.
April is hot and busy around Songkran.
Seasonal Callouts Timeline
Whale shark chances in the Gulf
JanJanFebFebMarMarAprAprMayMayJunJunJulJulAugAugSepSepOctOctNovNovDecDecIn the calmer spring window, Koh Tao is known for increased whale-shark odds on offshore pinnacle days. Sightings are never guaranteed, so plan for great reef diving first and treat big animals as a bonus.
Manta rays and pelagic surprise days in the Andaman
JanJanFebFebMarMarAprAprMayMayJunJunJulJulAugAugSepSepOctOctNovNovDecDecDuring the open-season window, offshore routes from Khao Lak for the Similan Islands can produce manta rays and other pelagics, especially on current-washed pinnacles.
Similan and Surin seasonal reopening
JanJanFebFebMarMarAprAprMayMayJunJunJulJulAugAugSepSepOctOctNovNovDecDecSome years, the Andaman marine-park season restarts around mid-October. Book early if your trip targets the first weeks after reopening.
Songkran travel surge
JanJanFebFebMarMarAprAprMayMayJunJunJulJulAugAugSepSepOctOctNovNovDecDecSongkran (Thai New Year) can spike domestic travel demand. If you travel in April, lock in flights and ferries early and expect busy towns and beaches.