What the flags mean
The system is simple and worth memorising before you arrive, because a flag on a pole is easy to walk past when the water looks inviting and you have flown a long way to swim in it.
| Flag | Meaning |
|---|---|
| Two red flags | Beach closed, no water activities at all |
| One red flag | Dangerous conditions, swimming prohibited |
| Yellow flag | Proceed with caution |
| Red and yellow | Lifeguard present, swimming permitted in that zone |
Thai government guidance adds two rules alongside the flags: swim only in designated areas, and stop water activities during and after heavy rain, when rip currents and shore break become more dangerous.
When this applies
Thailand's rainy season begins in mid-May when the southwest monsoon arrives, and the southern region sees the most prolonged rainfall of any part of the country. Phuket sits on the Andaman coast, facing that monsoon directly, so the months that follow bring rougher seas and more frequent red flags.
Government information services have reported Phuket beaches including Patong, Surin, Nai Harn, Kata and Karon being red-flagged on the basis of regional meteorological guidance, with lifeguards instructing visitors to stay out of the water. This is a normal seasonal occurrence rather than an emergency, and it is why a beach holiday booked into these months needs a plan for days when swimming is not an option.
Checking before you go in
The Thai Meteorological Department publishes a shipping and marine forecast in English covering the Andaman Sea, with wave heights and monsoon conditions. It is written for vessels rather than swimmers, which makes it more useful than a generic weather app: it tells you what the sea is doing rather than whether it will rain.
Read it in the morning, then read the beach itself when you arrive. The flag reflects conditions where you are standing, and conditions vary between beaches on the same island on the same day.
If you get caught in a rip current
Thailand's Department of Disaster Prevention and Mitigation operates a 24-hour hotline on 1784. Save it before you need it.
Planning a monsoon-season trip
Rough water does not ruin a Phuket trip; it changes it. Phuket Old Town, the food, the viewpoints, the sheltered eastern side of the island and the spas are all unaffected by what the Andaman is doing. Book accommodation you would be happy in for a rainy afternoon, keep boat trips flexible, and treat any day of flat calm sea as a bonus rather than the plan.
If swimming and island-hopping are the entire point of your trip, the honest advice is to travel outside the monsoon months rather than to hope.