Why the two coasts differ
Thailand's southern peninsula is a narrow strip of land with the Andaman Sea on its western side and the Gulf of Thailand on its eastern side. The mountains that run down its spine do the rest. From roughly May to October the southwest monsoon drives moist air off the Indian Ocean directly onto the Andaman coast, which takes the brunt of it. From roughly October to January the northeast monsoon brings the heavier weather down onto the Gulf coast instead.
The result is two coasts a couple of hundred kilometres apart with high seasons that barely overlap. Phuket, Krabi, Khao Lak and Phang Nga on the Andaman side are at their finest from November to April. Koh Samui, Koh Phangan and Koh Tao on the Gulf side are generally at their finest from roughly February through to August or early September. For a readership whose travel window is fixed by the Gulf summer, that second sentence is the useful one.
None of this is absolute. Both coasts get rain in every month, both coasts get fine days in their off seasons, and any single week can defy the pattern entirely. What the pattern gives you is a better than even chance, and across a long stay a better than even chance is what planning is made of.
Month by month, side by side
| Month | Andaman: Phuket, Krabi, Khao Lak | Gulf: Samui, Phangan, Koh Tao |
|---|---|---|
| January | Peak season. Dry, calm sea, highest prices | Recovering from the wet months, improving through the month |
| February | Peak season. Excellent conditions | Generally good and drying out |
| March | Very good, heat building | Very good, one of the better months |
| April | Hot, still largely dry, season ending | Hot and generally dry |
| May | Monsoon usually arrives, sea roughening | Some rain, sea usually workable |
| June | Wet season established, rates fall | Often good. A strong month on this coast |
| July | Wet, green, rough west-facing sea | Often among the drier months. Good for Gulf families |
| August | Wet, similar to July, occasional strong systems | Generally good, some rain building late |
| September | Typically the wettest month. Many closures | Rain increasing, still often serviceable |
| October | Wet, improving late in the month | Wet season beginning in earnest |
| November | Season turning. Often very good from mid-month | Typically the wettest month here |
| December | Peak season, dry, busiest and priciest | Wet, improving toward the end of the month |
Read the July and August rows next to each other and the whole argument of this guide is visible in two lines. The same fortnight that delivers a green, quiet, discounted and frequently wet Phuket can deliver a bright and calm Samui, and the flight between them is under an hour and a half via Bangkok, or a road and ferry combination from the mainland.
What this means for a Gulf summer
If the family's summer requires reliable sea swimming, sailing, diving or long beach days, the Gulf coast is the correct choice in June, July and August, and Samui is the natural anchor. If the family's summer is really about a large private villa, a pool, a garden and privacy, with the sea as a view rather than a programme, Phuket becomes very attractive indeed because green-season rates on the Andaman side are materially lower and the best villas are actually available.
Many of our clients do both, and the two-base summer is a pattern we recommend often: several weeks in a Phuket villa where the money buys space and staff, and a shorter Samui stretch booked closer to the date when the marine forecast is visible. Because Samui in summer is a known good, its better villas are not the bargain that Phuket's are in the same weeks. That is the trade, stated plainly: on the Gulf side you buy the weather, on the Andaman side you buy the property.
Getting to each of them
Phuket has an international airport with wide connectivity, including seasonal and year-round services from parts of the Gulf as well as constant domestic flights from Bangkok. Transfers from the airport to the northwestern beaches, Bangtao, Surin, Kamala and Layan, run roughly twenty to forty minutes; Patong, Kata and Karon are further. It is the easier island to reach with a large family and a quantity of luggage, and it is the easier island to reach in bad weather because arrival does not depend on a boat.
Samui's airport takes limited aircraft types and its capacity is correspondingly constrained, so flights are fewer and fares higher than the distance suggests. The alternative route is a flight to Surat Thani on the mainland followed by a road transfer and a ferry, which is perfectly civilised on a large vessel but adds hours and a weather dependency. Koh Phangan and Koh Tao are reached by ferry from Samui or the mainland, and for a household travelling with elderly relatives the additional leg is worth thinking about carefully.
Krabi has its own airport and serves Ao Nang and the Railay peninsula, with the same Andaman season as Phuket. Khao Lak sits north of Phuket airport and is quieter, more resort-led, and closes down noticeably in the wet months, which is worth knowing before booking a family into it in July.
The character of each, beyond the weather
Weather is not the only axis. Phuket is the largest and most developed, with the widest choice of luxury villas and resorts, the best hospitals of any Thai island, the most halal-certified dining and the largest Muslim population of the southern tourist islands, with mosques throughout. For a Gulf family that wants an island with genuine infrastructure behind it, Phuket has no real competitor.
Samui is smaller, greener and quieter, with strong villa privacy and a shorter list of everything else. Medical facilities exist but are not on Phuket's scale, which matters for families travelling with an elderly parent or a medical requirement. Koh Phangan is quieter still and more rustic, and certain nights of the month bring very large crowds to one part of the island for events that most of our clients would prefer to be nowhere near; we book around those dates as a matter of routine. Koh Tao is small, diving-led, and rarely the right answer for a large family.
Krabi and Ao Nang offer the limestone scenery that photographs better than anywhere else in Thailand, at a gentler pace and price than Phuket, with less depth of luxury inventory. Hua Hin, on the Gulf coast but on the mainland, sidesteps the island question entirely and follows the Gulf coast's rain pattern, which is part of why it works so well as a summer base.
How we choose for a client
The questions we ask are short. Does anyone in the party need to be near a major hospital. Does the family actually swim in the sea or does it use the pool. How many people and how much luggage, which decides whether a ferry leg is acceptable. Are the dates fixed by school terms or movable. And is the priority the property or the weather, because in July those two answers point at different coasts.
From five answers the coast usually selects itself, and only then do we start naming properties. Doing it the other way round, starting with a villa someone admired in a photograph, is how families end up in Khao Lak in September.
Seasonal patterns here are long-run tendencies, not forecasts. Confirm current conditions with the Thai Meteorological Department, verify island national park opening periods with the Department of National Parks, Wildlife and Plant Conservation, and check ferry operating status with the operator on the day of travel.
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This briefing is general information, not legal, tax or investment advice. Thai rules change frequently and individual cases differ. Verify current requirements with the relevant authorities, including the Immigration Bureau, the Board of Investment, the Land Department, the Department of Business Development and the Revenue Department, and take advice on your own facts before acting.
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