Ryotu Ko (JPRYO) — marine weather & port guide
Ryotu Ko is a port in Japan at 38°5.0′N 138°34.0′E. Today (Aug 3): ESE wind 20–24 kn, waves 1.2–1.4 m, from the ECMWF IFS run 2026-08-03 12z. The live chart on this page shows current conditions and plans weather-optimized departures from this harbor.
Port facts (NGA World Port Index)| Position | 38°5.0′N 138°34.0′E |
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| UN/LOCODE | JPRYO |
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| Harbor size | Very small |
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| Harbor type | Coastal natural harbor |
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| Shelter | Fair |
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| Channel depth | 19 m |
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| Anchorage depth | 23 m |
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| Tide range | 1 m |
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| Time zone | Asia/Tokyo |
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10-day marine forecast — Ryotu Ko
| Date | Wind | Gusts | Waves |
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| ESE 20–24 kn | 34 kn | 1.2–1.4 m |
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| ESE 15–21 kn | 29 kn | 0.8–1.1 m |
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| E 5–14 kn | 21 kn | 0.3–0.7 m |
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| ENE 4–9 kn | 14 kn | 0.2–0.4 m |
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| NE 2–5 kn | 9 kn | 0.1–0.2 m |
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| NNW 7–15 kn | 18 kn | 0.2–0.7 m |
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| ENE 5–16 kn | 20 kn | 1.0–1.4 m |
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| ESE 10–10 kn | 20 kn | 0.9–0.9 m |
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| NW 5–5 kn | 14 kn | 0.7–0.7 m |
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| NNE 7–7 kn | 10 kn | 1.1–1.1 m |
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Forecast from the ECMWF IFS model run , waves from ECMWF WAM. Updated with each model cycle; the live chart below recalculates for your departure time and vessel.
Frequently asked
How is the weather at Ryotu Ko right now?
As of the ECMWF IFS run 2026-08-03 12z: ESE wind 20–24 kn, waves 1.2–1.4 m. The 10-day outlook is in the forecast table on this page and updates with each model cycle.
How big is the harbor at Ryotu Ko?
Ryotu Ko is classed as a very small harbor (coastal natural harbor), with fair shelter in the NGA World Port Index.
How deep is the approach to Ryotu Ko?
Per the NGA World Port Index, the entrance channel carries about 19 m and anchorage depths run about 23 m. Verify against current official charts before entry.
What restricts entry to Ryotu Ko?
Entry is affected by heavy swell, overhead clearance limits. Check the live forecast on this page and official notices before approach.