Koh Sak Conditions
Live 7-day dive conditions forecast for Koh Sak in the Gulf of Thailand — useful for both freediving and scuba diving. Scored on wind (with per-site directional exposure), waves, swell, ocean current, visibility and tides. 4-model ensemble-averaged, calibrated by instructor reports.
Last update: Mon 20 Apr, 02:11 UTC · Timezone shown: Asia/Bangkok
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20 Apr
21 Apr
22 Apr
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24 Apr
25 Apr
26 Apr
Full Data Behind the Score
Every signal we use. Verify against your own readings — Windguru, Windy, your dive log. If it disagrees with reality, log your dive and we'll calibrate.
| Date | Scorei | Windi | Gusti | Diri | Wavesi | Wave diri | Periodi | Swelli | Currenti | Cur diri | SSTi | Rain 7di | Chl-ai | Bloomi | Tide rangei | CAPEi | Stormi | Modelsi | Spreadi | Factorsi |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mon 20 Apr | 58 | 21.9 | 21.9 | S | 0.72 | S | 3.4s | 0.26 | 3.10 | N | 30.8° | 2.2 | 0.63 | 0.28 | 1.18m | 0 | low | 4 | 10.7 | strong current, forecast uncertainty |
| pts | 58/100 | wind 21/30 | waves 14/20 · swell 10/10 | current 0/20 | viz 13/15 | tide 0 | GFS 36.6 ICON 14.5 JMA 13.3 GEM 23 | |||||||||||||
| Tue 21 Apr | 58 | 20.8 | 19.7 | S | 0.74 | S | 3.3s | 0.46 | 3.20 | N | 30.8° | 2.7 | 0.63 | 0.28 | 1.27m | 0 | low | 4 | 10.0 | strong current, forecast uncertainty |
| pts | 58/100 | wind 21/30 | waves 14/20 · swell 10/10 | current 0/20 | viz 13/15 | tide 0 | GFS 35.2 ICON 15.7 JMA 12.8 GEM 19.4 | |||||||||||||
| Wed 22 Apr | 54 | 22.8 | 22.8 | S | 0.80 | S | 3.5s | 0.56 | 2.90 | N | 30.9° | 5.3 | 0.63 | 0.28 | 1.31m | 0 | low | 4 | 10.5 | strong current, forecast uncertainty |
| pts | 54/100 | wind 21/30 | waves 14/20 · swell 6/10 | current 0/20 | viz 13/15 | tide 0 | GFS 37.3 ICON 17 JMA 13.4 GEM 23.4 | |||||||||||||
| Thu 23 Apr | 58 | 23 | 22.5 | S | 0.70 | S | 3.4s | 0.48 | 2.70 | N | 30.9° | 5.3 | 0.63 | 0.28 | 1.29m | 0 | low | 4 | 9.6 | strong current, forecast uncertainty |
| pts | 58/100 | wind 21/30 | waves 14/20 · swell 10/10 | current 0/20 | viz 13/15 | tide 0 | GFS 35.4 ICON 17.7 JMA 13.6 GEM 25.2 | |||||||||||||
| Fri 24 Apr | 57 | 22.8 | 21.1 | S | 0.68 | S | 3.3s | 0.42 | 2.00 | N | 30.9° | 6.8 | 0.63 | 0.28 | 1.20m | 0 | low | 4 | 10.1 | strong current, forecast uncertainty |
| pts | 57/100 | wind 21/30 | waves 14/20 · swell 10/10 | current 0/20 | viz 12/15 | tide 0 | GFS 36.6 ICON 16.3 JMA 14.3 GEM 23.8 | |||||||||||||
| Sat 25 Apr | 57 | 18.5 | 17.9 | S | 0.50 | S | 2.9s | 0.34 | 1.40 | NE | 30.9° | 5.8 | 0.63 | 0.28 | 1.25m | 0 | low | 4 | 10.1 | strong current, forecast uncertainty |
| pts | 57/100 | wind 21/30 | waves 14/20 · swell 10/10 | current 0/20 | viz 12/15 | tide 0 | GFS 32.4 ICON 15.1 JMA 8.6 GEM 18 | |||||||||||||
| Sun 26 Apr | 63 | 17.4 | 17.8 | S | 0.34 | S | 2.8s | 0.26 | 1.30 | SE | 30.9° | 7.6 | 0.63 | 0.28 | 0.20 | 0 | low | 4 | 13.1 | strong current, forecast uncertainty |
| pts | 63/100 | wind 21/30 | waves 20/20 · swell 10/10 | current 0/20 | viz 12/15 | tide 0 | GFS 35.7 ICON 12 JMA 5.1 GEM 16.9 | |||||||||||||
Reading the table: Each row shows one day. Below the values, a points row breaks down where the score came from — e.g. wind 22/30 means you earned 22 of 30 possible wind-points.
Click the small (i) icons next to any column header to see a plain-English explanation of what the metric means and how to read it.
Sources: Wind/gust/direction and CAPE ensemble-averaged across GFS, ICON, JMA and GEM models. Waves, swell, ocean current, SST from Open-Meteo Marine. Tides from WorldTides FES2022. Chlorophyll from Copernicus Marine Service satellite. Calibrated by instructor reports.
How the score works
Out of 100, weighted for what matters underwater (freediving + scuba):
- Wind (30pts) — with per-site exposure: sheltered sites get credit when wind blows from the sheltered quarter.
- Waves (20pts) — surface chop, boat-ride comfort.
- Swell (10pts) — ruins line work and bottom visibility at depth.
- Ocean current (20pts) — from Open-Meteo Marine ocean currents. Matters for both sports.
- Viz (15pts) — combines satellite chlorophyll + 7-day rainfall runoff + seasonal bloom.
- Spring-tide penalty (−0 to −5) — applies only to shallow coastal sites (≤20m).
Forecast is ensemble-averaged across ECMWF and GFS models. When they disagree by >8 km/h we flag "forecast uncertainty."
Sources & caveats
Data comes from Open-Meteo Marine and ECMWF weather models. Hover a cell for full metrics. Local factors the models can't see — boat traffic at Sail Rock, plankton blooms for whale-shark season, thermocline depth — still matter. Text us on WhatsApp for same-day conditions from the crew.
Why we built this
The most accurate Gulf of Thailand dive forecast — because the existing ones aren't
For years we relied on Windguru, Windy, and local weather apps to decide whether to run our boats. Every one of them is built for sailors — not divers. They tell you the wind speed and the wave height. They don't tell you there's a 0.8 m/s current ripping through Sail Rock that'll make your dive miserable — freediving or scuba. They don't know a plankton bloom just crashed visibility. They don't care about the thermocline at 18m, the spring-tide pull, or whether your specific dive site is sheltered from today's wind.
So we built our own. This tracker blends four weather models (GFS, ICON, JMA, GEM — averaged together), Open-Meteo's ocean data (waves, swell, ocean currents, sea-surface temperature, wave direction and period), real tide predictions from WorldTides FES2022, satellite chlorophyll-a from Copernicus Marine as a direct visibility proxy, and atmospheric storm energy (CAPE) for thunderstorm risk. Then we score it for what matters underwater — not generic weather.
The final layer is you. Every instructor and diver who logs a post-dive report — what they actually saw, the real visibility, the real current — calibrates the forecast. Over time, ground-truth beats any algorithm. If you're diving in the Gulf, drop your report. It takes 30 seconds and makes the next boat-load of divers safer.
Get notified when it's a good day
Alert me when Koh Sak is diveable
One email the first time the forecast crosses your threshold — max one notification every 3 days. No spam.
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Frequently Asked Questions
How accurate is the Gulf of Thailand dive conditions forecast? +
What does the dive condition score mean? +
Why is Sail Rock's score different from Windguru's wind forecast? +
When is the best diving season in Koh Samui and Koh Tao? +
How do I report actual dive conditions to improve the forecast? +
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