Is the Andaman Sea rough? What to expect on the crossing
It depends on the season. From November to April the winds are weaker, and from May to September strong south-westerlies blow, with mean wind speeds touching 8 m/s in June, July and August. Tigerline lists Phuket to Koh Phi Phi at about 45 minutes, and it runs a separate monsoon timetable for May to September.
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Sea · Thailand and the Andaman Islands · Reputation among passengers: mixed: commonly reported as uncomfortable in the wrong conditions.
- Low
- Moderate
- High
- Very high
Roughness summarises typical reported conditions for this crossing, not a forecast for any given sailing.
Monsoon winds over deep open water
In the Nausea Index table of the 121 sea crossings we cover, the Andaman Sea is rated manageable, one of 81 in that band, with 40 rated higher. Full table: the roughest sea crossings, ranked.
Key facts
- The Andaman Sea is a sea, and passenger reports place it in the moderate roughness band.
- The mechanism behind that reputation: Monsoon winds over deep open water.
- Conditions are reported roughest in June, July and August.
- The calmest months are usually January, February, March, April, November and December.
Why does the Andaman Sea get rough?
The Andaman Sea is up to 1,202 km long and 647 km wide, with an average depth of 1,096 m. Its climate follows the monsoons: north-easterlies average 5 m/s from November to February, weaken by March and April, then reverse to strong south-westerlies from May to September, with mean wind speeds touching 8 m/s in June, July and August. Wind speeds drop by October and switch back to north-easterlies from November. Tides are semi-diurnal with an amplitude of up to 7.2 m.
When is the Andaman Sea roughest?
Strong south-westerlies run from May to September and peak from June to August, and wind speeds drop by October. Wave reanalysis data (ERA5) for the open sea off Phuket and off the Andaman Islands ranks August and July roughest, then June and September, and March and April calmest. Tigerline publishes a separate monsoon-season timetable for May to September 2026, and says it adjusts schedules for route, season and weather. Wikipedia says that in the low season, from mid June to mid October, the only way to Koh Lipe is the speedboat from Pak Bara.
| Roughest water in Jan | Roughest water in Feb | Roughest water in Mar | Roughest water in Apr | Roughest water in May | Roughest water in Jun | Roughest water in Jul | Roughest water in Aug | Roughest water in Sep | Roughest water in Oct | Roughest water in Nov | Roughest water in Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Calm | Calm | Calm | Calm | Mixed | Roughest | Roughest | Roughest | Rough | Mixed | Calm | Calm |
Typical seasonal pattern, not a forecast. Any month can deliver a calm crossing or a bad one. Check the marine forecast for your sailing date. Select a month to see every sea and ferry crossing ranked for it.
Where to be on board
Front to back
- Bow (front)Avoid
- MidshipBest
- Stern (aft)OK
The crossing: About 30 minutes to 5 hours
Roughest stretch: The open water between the islands and the mainland coast
Sit midship and as low as the boat allows, away from the bow, and keep your eyes on the horizon.
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The crossings that cross it
| Route | Typical duration | What to know |
|---|---|---|
| Phuket to Koh Phi Phi | About 45 minutes | Tigerline lists about 14 trips daily. |
| Koh Phi Phi to Koh Lanta | About 30 minutes | Tigerline lists about 6 trips daily. |
| Phuket to Koh Lipe | About 4 to 5 hours | The longest Tigerline route on this list, with about 4 trips daily. Wikipedia says that from mid June to mid October the only way to Koh Lipe is the speedboat from Pak Bara. |
| Port Blair to Havelock | About 1 hour 30 minutes | Makruzz's schedule lists a 06:00 departure and a 07:30 arrival. Wikipedia says the Havelock ferry sailing is subject to weather conditions. |
What helps on this crossing
- Choose the ferry if motion bothers you. Tigerline lists being sensitive to motion and preferring stability as a reason to pick a ferry over a speedboat, and calls the ferry a smoother ride in moderate sea conditions. The speedboat takes about a third of the ferry's time.
- Travel between November and April if you can. The winds are weaker then, while June to August has the strongest south-westerlies.
- Sit midship, keep your eyes on the horizon and put your phone away for the crossing.
For the full toolkit see the seasickness guide, or what to do once it has already started. For what the trials actually say about the oldest trick on that list, see the verdict on looking at the horizon. If the rocking follows you ashore afterwards, that is land sickness, which is normal, and it passes.
Frequently asked questions
Is the Andaman Sea rough in July?
Yes, at times. July is in the strongest part of the south-westerly monsoon: the winds blow from May to September and mean speeds touch 8 m/s in June, July and August. Tigerline runs a separate monsoon timetable for May to September 2026 and adjusts schedules for weather.
Is the Andaman Sea rough in January?
Usually less. North-easterly winds average 5 m/s from November to February, against mean speeds touching 8 m/s in June, July and August. Wikipedia says the Langkawi to Koh Lipe ferry operates from mid October until mid May.
How long is the boat from Phuket to Koh Phi Phi?
Tigerline lists about 45 minutes with about 14 trips daily. It lists Koh Phi Phi to Koh Lanta at about 30 minutes and Phuket to Koh Lipe at 240 to 300 minutes.
Is a speedboat or a ferry better in rough weather?
Tigerline describes the ferry as a smoother ride in moderate sea conditions and the speedboat as smooth on calm sea, and lists being sensitive to motion as a reason to choose a ferry. The speedboat takes about a third of the ferry's time.
Other crossings
Sources & further reading
- https://en.wikipedia.org/wiki/Andaman_Sea
- https://en.wikipedia.org/wiki/Ko_Lipe
- https://en.wikipedia.org/wiki/Havelock_Island
- https://www.tigerlineferry.com/
- https://www.tigerlineferry.com/time-table
- https://www.tigerlineferry.com/blog/speedboat-vs-ferry-which-should-you-choose-for-island-travel-in-thailand-k5cgd9
- https://www.makruzz.com/web/cms/fares
- https://open-meteo.com/en/docs/marine-weather-api
Sea conditions described here are typical patterns drawn from published marine and operator information as of July 2026, not a forecast: conditions on any given sailing depend on the weather that day, and any month can deliver a calm crossing or a bad one. Route and operator names are trademarks of their respective owners; Dizzout is not affiliated with or endorsed by them. Seasickness sensitivity varies from person to person; this page is informational and not medical advice.