Onahama Ko marine weather forecast
Onahama Ko (JPONA) is a port in Japan at 36°56.0′N 140°54.0′E. Today (Sep 15): NNE wind 12–15 kn, waves 1.5–1.6 m, from the NOAA GFS run 2026-09-15 18z. The live chart on this page shows current conditions and plans weather-optimized departures from this harbor.
Port facts (NGA World Port Index)| Position | 36°56.0′N 140°54.0′E |
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| UN/LOCODE | JPONA |
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| Harbor size | Small |
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| Harbor type | Coastal breakwater harbor |
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| Shelter | Good |
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| Channel depth | 11 m |
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| Anchorage depth | 23 m |
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| Tide range | 3 m |
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| Pilotage | Advisable |
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| Time zone | Asia/Tokyo |
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Facilities & services (NGA World Port Index)| Tugs | Assistance available |
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| Supplies | Fuel oil, water |
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| Repairs | Limited |
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| Medical facilities | Available |
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10-day marine forecast — Onahama Ko
| Date | Wind | Gusts | Waves |
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| NNE 12–15 kn | 15 kn | 1.5–1.6 m |
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| NE 16–24 kn | 26 kn | 1.7–2.6 m |
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| NNE 22–27 kn | 29 kn | 2.6–2.8 m |
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| NNE 16–21 kn | 24 kn | 2.2–2.5 m |
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| NNE 10–12 kn | 14 kn | 2.8–3.2 m |
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| E 15–15 kn | 24 kn | 3.1–3.1 m |
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| NNW 13–13 kn | 22 kn | 4.2–6.3 m |
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| ENE 6–6 kn | 6 kn | 2.0–2.0 m |
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| W 7–7 kn | 9 kn | 1.2–1.2 m |
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| NW 9–9 kn | 10 kn | 0.8–0.8 m |
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Forecast from the NOAA GFS model run , waves from ECMWF WAM. Updated with each model cycle; the live chart below recalculates for your departure time and vessel.
What to watch in the forecast
Across the loaded 10-day outlook, the strongest daily modeled wind reaches 27 kn on Sep 17. The highest modeled significant wave height is 6.3 m on Sep 21. Compare the dated model run with official forecasts and warnings before departure.
Frequently asked
How is the weather at Onahama Ko right now?
As of the NOAA GFS run 2026-09-15 18z: NNE wind 12–15 kn, waves 1.5–1.6 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 Onahama Ko?
Onahama Ko is classed as a small harbor (coastal breakwater harbor), with good shelter in the NGA World Port Index.
How deep is the approach to Onahama Ko?
Per the NGA World Port Index, the entrance channel carries about 11 m and anchorage depths run about 23 m. Verify against current official charts before entry.
What restricts entry to Onahama Ko?
Entry is affected by tidal windows, heavy swell. Check the live forecast on this page and official notices before approach.