Rip currents are the main reason swimmers drown off Thailand's beaches, and they are strongest during the monsoon, which on the Andaman coast (Phuket, Khao Lak, Krabi) runs from about May to October. A red flag means do not swim; if a current pulls you out, do not fight it, swim parallel to the beach and come back in at an angle.
Thailand's sea looks gentle in the brochures, and for much of the year it is. But the west-facing beaches take the full force of the southwest monsoon, and the waves that roll in create strong channels of water flowing back out to sea. Every rainy season brings reports of visitors swept out from popular beaches in Phuket. The UK government's travel advice says plainly that people have drowned in strong riptides, especially in monsoon season.
This page explains what a rip current is, how to read the flags Thai lifeguards use, which coasts are risky in which months, and what to do if you or someone else is caught. For jellyfish, see our separate page on box jellyfish and first aid.
Beach flags used in Thailand (Tourism Authority of Thailand)
- Red
- Do not swim
- Yellow
- Swimming allowed, medium risk, take care
- Green
- Calm conditions for swimming
- Red and yellow
- Lifeguards on duty
- Black and white checkered
- Area for boats, surfboards and other watercraft
- Emergency
- 1669 ambulance, 191 police
What a rip current is, and why it drowns strong swimmers
A rip current is a narrow, fast channel of water flowing away from the shore, out through the breaking waves. The US ocean agency NOAA says rips can move at up to eight feet (about 2.4 meters) per second, faster than an Olympic swimmer. They do not pull you under. They carry you out.
The danger comes from what people do next. NOAA explains that panicked swimmers try to swim straight back to shore against the current and drown from exhaustion. A rip can form on a beach that looked calm an hour earlier, and it can be strongest at low tide, as in the case of a man swept away at Naithon Beach in Phuket in May 2026, whom a lifeguard saw struggling in the outer wave zone at low tide.
Signs of a rip, according to NOAA's US National Weather Service, include a darker, narrow gap between breaking waves, a channel of choppy water heading out, foam or sand moving seaward beyond the breakers, and a line of debris drifting out. Polarized sunglasses make the color difference easier to see. On many Thai beaches the safest assumption in the monsoon is simply that a rip may be there.
Which coasts are risky, and when
The pattern follows the monsoons. The Tourism Authority of Thailand describes the southwest monsoon as running from May to October, and warns that large waves and "unseen threats like rip-currents" can make swimming very dangerous in places like Phuket and the Andaman islands then. The UK government gives the same rainy season, May to October, for most of Thailand, but notes that Koh Samui and the southeast usually get their rain from November to March.
| Coast | Main risk months | Examples |
|---|---|---|
| Andaman Sea (west coast) | About May to October | Phuket's west coast, Khao Lak, Krabi beaches, Koh Lanta |
| Gulf of Thailand, Samui area and south-east | Usually November to March (UK government wording) | East-facing beaches on Koh Samui and Koh Phangan |
Phuket gets the most attention because so many visitors swim there in the low season. In June 2024 an American and a Thai woman drowned off Mai Khao Beach and a Russian man off Surin Beach within days, and a US citizen had been found at Nai Harn shortly before; lifeguards put up red flags on unsafe beaches. In May 2026 lifeguards raised red flags along Naithon Beach and walked the sand telling people not to enter the water at all. Our Phuket guide describes the island's beaches and the more sheltered east coast, and the comparison of Phuket's beaches goes beach by beach.
For a wider view of the seasons, our pages on the best time for the Thai islands and on traveling in the rainy season explain how the two coasts differ.
How to read Thai beach flags
Thailand uses a flag system on beaches with lifeguards, and the UK travel advice tells visitors to follow all warning signs, especially red flags. The Tourism Authority of Thailand gives the meanings in the factbox above. Two points matter most in practice.
First, a red flag is a ban, not advice. When lifeguards plant red flags, they are telling you that conditions are dangerous for everyone, including strong swimmers. Second, the red-and-yellow flag marks where lifeguards are watching. Swim between those flags, or near the lifeguard tower, and nowhere else on the beach.
The absence of any flag does not mean the sea is safe. Many smaller beaches have no lifeguards and no flags at all. We could not find an official list of which Thai beaches have lifeguards, in which months or at what hours, so check with your hotel or the lifeguard post when you arrive. The tourism authority's own advice is the same: if in doubt, ask the lifeguards or your hotel staff.
Red flags on Phuket's west coast mean stay out, even knee-deep. When the Naithon lifeguards raised red flags in May 2026, they also told tourists not to enter the water under any circumstances. A rip starts close to the shoreline, so wading out "just to cool off" puts you in reach of it.
If you are caught in a rip current
- Do not fight it. You will not out-swim it, and trying will exhaust you.
- Swim parallel to the shore, along the beach, until you feel the pull ease. NOAA's advice is to swim parallel and then come back to land at an angle.
- If you cannot swim out of it, float. Stay calm, keep your head up, and let the current carry you; most rips weaken beyond the breaking waves.
- Raise an arm and shout to attract attention.
- Swim back in at an angle, away from the channel, using the waves to help you.
If someone else is in trouble
Many drownings include a second victim who went in to help. In the June 2024 Mai Khao case, police said one person was swept away by the current while the other tried in vain to help. Do this instead:
- Alert a lifeguard at once, or call 1669 for an ambulance and 191 for the police; our page of emergency numbers in Thailand has the full list.
- Throw something that floats: a bodyboard, a cooler, a life ring if there is one.
- Shout instructions: tell them to swim parallel to the beach.
- Keep them in sight and point to them so rescuers know where to look.
Plan your swims for the morning in the low season. Lifeguards are more likely to be on duty in daytime, and you can check the flags and ask about conditions before going in. Never swim alone, after drinking, or at night.
Rivers and waterfalls are a separate hazard in the rainy season. The UK government warns that currents near waterfalls and in rivers can be extremely strong, and flash floods hit waterfall areas quickly. Our general article on what never to do in Thailand lists swimming in unknown waters among the classic mistakes; the health and safety hub has the rest of our safety guides.
Frequently asked questions
What does a red flag mean on a Thai beach?
Do not swim. The Tourism Authority of Thailand says a red flag means the sea is not safe for swimming. Yellow means swimming is allowed with care, green means calm, and a red-and-yellow flag marks a stretch watched by lifeguards.
When is it dangerous to swim in Phuket?
Mainly during the southwest monsoon, about May to October, when large waves and rip currents hit the west-coast beaches. Drownings in recent years have happened at Naithon, Mai Khao, Surin and Nai Harn. Follow the flags and lifeguards every day.
How do I escape a rip current?
Do not swim against it. Swim parallel to the shore until the pull eases, then swim back at an angle. If you cannot, float, stay calm and wave for help. Rip currents carry you out, not under.
Do all Thai beaches have lifeguards?
No. Lifeguards work at designated beaches, mainly busy ones, and many smaller beaches have none. We could not find an official list of covered beaches and hours, so ask your hotel or check for a lifeguard tower before swimming.
Sources
- Tourism Authority of Thailand – Important information on marine tourism during the southwest monsoon season (checked October 2026)
- UK FCDO – Thailand travel advice: Safety and security (checked October 2026)
- NOAA National Ocean Service – What is a rip current? (checked October 2026)
- US National Weather Service – Rip current science (checked October 2026)
- Bangkok Post – Man swept out to sea amid strong winds in Phuket (May 2026) (checked October 2026)
- Bangkok Post – 2 foreign men, 1 Thai woman drown off Phuket beaches (June 2024) (checked October 2026)