Gulf of Thailand weather and tide outlook: 17–22 August 2025
This Gulf of Thailand weather and tide forecast covers Koh Samui, Koh Phangan, Koh Tao and Surat Thani for the week of 17 to 22 August 2025. It is a snapshot of expected temperatures, rainfall, sailing conditions and tides, published to help you plan ferry and transfer travel across the islands.
Gulf of Thailand Weather Forecast (Samui/Phangan/Tao/Surat Thani) August 17 to 22 August, 2025.
Day-by-day forecast
- Sunday, August 17 — Temperature: 32–26°C. Weather: Heavy rain, 60% of area. Sailing Conditions: Moderate, waves up to 2 m. Tide: Low tide morning, rising midday.
- Monday, August 18 — Temperature: 33–27°C. Weather: Heavy rain, 40% of area. Sailing Conditions: Moderate, waves 1.5–2 m. Tide: High tide early morning, low tide afternoon.
- Tuesday, August 19 — Temperature: 33–27°C. Weather: Heavy rain, 40% of area. Sailing Conditions: Moderate, waves up to 2 m. Tide: Low tide morning, rising later.
- Wednesday, August 20 — Temperature: 33–27°C. Weather: Heavy rain, 40% of area. Sailing Conditions: Moderate, waves 1.5–2 m. Tide: Rising in afternoon.
- Thursday, August 21 — Temperature: 33–27°C. Weather: Heavy rain, 40% of area. Sailing Conditions: Moderate, waves around 2 m. Tide: High tide early afternoon.
- Friday, August 22 — Temperature: 33–27°C. Weather: Heavy rain, 40% of area. Sailing Conditions: Moderate, waves above 2 m during storms. Tide: Lowering in evening.
What changed this week
Sunday, 17 August is the wettest day in the period, with heavy rain over 60% of the area and the coolest daytime high of 32°C. From Monday onwards, rain coverage settles at 40% and temperatures hold steady at 33–27°C.
The sea state is the detail worth watching. Conditions stay moderate for most of the week, with waves between 1.5 m and 2 m, then deteriorate on Friday, 22 August to moderate to rough, with waves above 2 m during storms.
Who this affects
Anyone crossing between the mainland and the islands during these dates. That includes passengers on Surat Thani to Koh Samui services, Koh Samui to Koh Phangan hops, and the longer legs out to Koh Tao, which sit in more open water and tend to feel swell first.
Smaller, faster craft are the most sensitive to a 2 m sea; larger vehicle ferries generally ride it better. Combined bus-and-ferry or minivan-and-ferry journeys are also affected, because a delayed crossing can push back the onward connection.
Practical impact for travellers
- Build slack into travel days. Avoid booking a same-day flight or long-distance onward leg immediately after a crossing, especially on Friday, 22 August.
- Expect possible delays, re-timing or cancellation if operators judge the sea unsafe. Decisions are made locally, close to departure.
- Tides shift boarding at shallower piers. Low tide mornings on 17 and 19 August, and the evening drop on 22 August, are the periods most likely to affect pier access.
- Pack rain gear in hand luggage and keep electronics in a dry bag — open-deck seating gets wet in heavy rain and spray.
- Check your operator's terms for weather cancellations before you travel, as refund and rebooking rules vary.
Planning around the sea state
Where your dates allow flexibility, earlier departures in this window are the calmer choice. Morning sailings are also generally steadier than late-afternoon ones during storm-prone periods.
Check routes and travel times
Live departure times, journey durations, operators and fares for each crossing are shown on the route pages. Compare options for Surat Thani to Koh Samui ferries, Koh Samui to Koh Phangan ferries and Koh Samui to Koh Tao ferries, or browse everything serving Koh Phangan and Koh Tao.
Disclaimer: Weather, sea conditions, and tide information are subject to change. Always check local updates and forecasts before planning activities.
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