Yakushima Diving Visibility Data — 157 Real Observations: 32m Summer, 17m Winter
2026-03-11
We analyzed 157 real dive log observations from Yakushima, a UNESCO World Natural Heritage site. The most surprising finding: July averages 32.1m visibility — significantly above Yonaguni (25.6m) and Ishigaki (20.9m), ranking among Japan's highest. The annual average is 24.8m, but spring (Mar–Apr) drops to 17–18m in a clear seasonal pattern.
24.8m
Annual avg
32.1m
July avg (peak)
17.1m
Mar avg (lowest)
157件
Real observations
Data period: May 2022 – March 2026
Monthly Visibility & Water Temperature
| Month | Vis (m) | Temp (°C) | Obs | Notes |
|---|---|---|---|---|
| Jan | 23.5m | 21.9°C | 5 | indicative (small n) |
| Feb | 19.8m | 19.4°C | 6 | indicative (small n) |
| Mar | 17.1m | 19.8°C | 6 | indicative (small n) |
| Apr | 18.4m | 21.8°C | 18 | |
| May | 23.1m | 23°C | 24 | |
| Jun | 25.2m | 25.8°C | 22 | |
| Jul | 32.1m | 27.8°C | 19 | annual peak |
| Aug | 30.2m | 29.1°C | 22 | |
| Sep | 27.2m | 28.1°C | 16 | |
| Oct | 21.1m | 25.7°C | 11 | |
| Nov | 22.1m | 24.8°C | 7 | indicative (small n) |
| Dec | 17.5m | 23°C | 1 | single obs only |
Summer Visibility Comparison: Yakushima Among Japan's Best
| Site | Jul | Aug | Sep | Annual |
|---|---|---|---|---|
| Yonaguni | 25.6m | 26.5m | 27.3m | 24.5m |
| Yakushima | 32.1m | 30.2m | 27.2m | 24.8m |
| Ishigaki | 20.9m | 21m | 21.4m | 20.5m |
| Kerama | 21.3m | 20.9m | 19.8m | 19.4m |
| Hachijojima | 20m | 19m | 19m | 17.2m |
Finding: Yakushima Summer Visibility Ranks Among Japan's Highest
July's 32.1m exceeds Yonaguni (25.6m) by +6.5m. The direct Kuroshio influence and strong summer stratification (thermocline) maintain clear deep water. However, with only 19 July observations, accuracy will improve as more data accumulates.
Yakushima's Visibility Pattern: Best in Summer, Lowest in Spring
Summer (Jun–Sep): 25–32m
When the Kuroshio approaches closest. Water temp 27–29°C with abundant tropical fish. Typhoon risk in Jul–Aug, but visibility is at its annual peak — Yakushima summer is among Japan's clearest periods.
Autumn (Oct–Nov): 21–22m
Post-typhoon season, relatively stable conditions. Water temp around 25°C is comfortable. Fewer observations, but still high visibility.
Winter (Jan–Feb): 20–24m
Only 5–6 observations, but 20–24m is solid. Water temp 19–22°C; 5mm wetsuit to drysuit recommended.
Spring (Mar–Apr): 17–18m
Annual lowest period. Spring plankton bloom has an effect. Still much higher than Izu spring levels (IOP April 10.1m).
Yakushima Diving: Wetsuit Guide
| Season | Water Temp | Suit |
|---|---|---|
| Jun–Sep (summer) | 25–29°C | 3mm wetsuit |
| Oct–Nov (autumn) | 24–26°C | 3–5mm wetsuit |
| Dec–Feb (winter) | 19–23°C | 5mm wetsuit – drysuit |
| Mar–May (spring) | 19–23°C | 5mm wetsuit |
About the Data
157 observations collected from Yakushima dive shop daily logs (May 2022 – Mar 2026). Months with fewer observations (especially winter) should be treated as indicative. Comparison sites use their full historical average. Yakushima data continues to accumulate.
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