Rain-Vulnerable Dive Sites: Where Heavy Rain Drops Visibility Most
2026-03-16
"It rained heavily yesterday — will the diving be okay tomorrow?" Every diver wonders. The answer varies dramatically by site. Some spots see massive visibility drops after heavy rain, while others barely notice. Using 46,000+ observations, we ranked sites by their vulnerability to rainfall.
-2.3m
Hachijojima (biggest drop)
-1.7m
IOP
-0.4m
Mikomoto (rain-resistant)
Top 5 Rain-Vulnerable Dive Sites
| Site | Dry | After Rain | Drop |
|---|---|---|---|
| Hachijojima | 20.8m | 18.5m | -2.3m |
| IOP | 16m | 14.3m | -1.7m |
| Kannoura | 9.5m | 8.9m | -0.6m |
| Futo | 11.8m | 11.2m | -0.6m |
| Hirasawa | 7.8m | 7.3m | -0.5m |
Why These Sites Are Rain-Vulnerable
Hachijojima (-2.3m)
Short, steep rivers on island flush sediment quickly after heavy rain
IOP (-1.7m)
Small rivers near Jogasaki Coast drain muddy water directly into the dive area
Kannoura (-0.6m)
Shallow harbor topography traps turbid water
Futo (-0.6m)
Small river inflow and shallow sand bed disturbance
Hirasawa (-0.5m)
Already low baseline visibility limits the absolute drop
Rain-Resistant Sites for Comparison
| Site | Dry | After Rain | Drop |
|---|---|---|---|
| Yonaguni | 25m | 24.2m | -0.8m |
| Mikomoto | 13m | 12.6m | -0.4m |
| Kerama | 19.8m | 19.3m | -0.5m |
What Makes a Site Rain-Resistant
Remote islands (no/few rivers), open-ocean sites (turbid water disperses quickly), and deep topography (surface turbidity doesn't reach depth). Mikomoto meets all three conditions, making it one of the most rain-resistant sites.
Reference: JAMSTEC 'Coastal Turbidity Dynamics' (https://www.jamstec.go.jp/e/)
Recovery Time After Heavy Rain
Recovery time after heavy rain depends heavily on site topography. Open-ocean sites benefit from tidal exchange, typically recovering in 1–2 days. Sheltered bay sites, where turbid water stagnates, may take 3–5 days to recover.
Fast Recovery (1–2 days)
Open-ocean sites like Mikomoto, Yonaguni, Kerama. Strong currents quickly disperse turbid water.
Slow Recovery (3–5 days)
Sheltered sites like Kannoura and Hirasawa. Turbid water lingers and bottom sediment gets re-disturbed.
Rainfall Impact in Our AI Model
In our AI model, rainfall ranks in the top 10 impact factors for visibility. However, rain's effect is indirect: rain → river flooding → sediment inflow → visibility drop. This delayed process is factored into the AI predictions.
Planning Dives After Heavy Rain
Diving at Hachijojima or IOP
Ideally wait 2+ days after heavy rain. Wait for river discharge to subside. Check our AI forecast for visibility recovery before departing.
Rainy Season Strategy
During the rainy season (June–July), prioritize rain-resistant sites. Mikomoto, Yonaguni, and Kerama maintain stable visibility throughout the rainy period.
About the Data
Visibility data from 46,000+ real dive logs. 'After heavy rain' filters observations where 48-hour cumulative rainfall exceeded 30mm prior to the dive. Precipitation data from Open-Meteo API (JMA database). Recovery times are estimated trends and vary significantly by topography, tides, and rainfall volume.
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