Is the East China Sea rough? What to expect on the crossing
Often, and it depends on the month. Wave reanalysis data (ERA5) puts the mean daily maximum wave height between 1.1 and 2.0 m in every month near Amami and Okinawa, with the 90th percentile above 3 m near Amami from July to September. On 18 October 2026, A-Line changed a port of call on a Naha to Kagoshima sailing because of rough seas.
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Sea · Southern Japan · Reputation among passengers: has a long-standing reputation for rough passages.
- Low
- Moderate
- High
- Very high
Roughness summarises typical reported conditions for this crossing, not a forecast for any given sailing.
Typhoons and fronts over a shallow sea
In the Nausea Index table of the 121 sea crossings we cover, the East China Sea is rated rough, one of 34 in that band, with 6 rated higher. Full table: the roughest sea crossings, ranked.
Key facts
- The East China Sea is a sea, and passenger reports place it in the high roughness band.
- The mechanism behind that reputation: Typhoons and fronts over a shallow sea.
- Conditions are reported roughest in October and December.
- The calmest months are usually April, May and June.
Why is the East China Sea so rough?
Most of the East China Sea is shallow, with almost three-fourths of it less than 200 m deep, and Kyushu and the Ryukyu Islands bound it on the east. The Kagoshima to Naha ferries run the length of the Ryukyu chain, calling at Amami Oshima, Tokunoshima, Okinoerabu, Yoron and Motobu before Naha. A-Line says weather and sea conditions change with typhoons and with the passage of cold and warm fronts. Wikipedia says Amami Oshima is subject to frequent typhoons.
When is the East China Sea roughest?
ERA5 data for 2000 to 2024 ranks December and October as the roughest months, with September and January close behind, and May and June as the calmest. Marix Line decides cancellations for Kagoshima departures by the morning of the sailing day, and a port change or conditional destination can stay open until just before departure. A-Line says weather and sea conditions change with typhoons and fronts, and Wikipedia says Amami Oshima is subject to frequent typhoons.
| Roughest water in Jan | Roughest water in Feb | Roughest water in Mar | Roughest water in Apr | Roughest water in May | Roughest water in Jun | Roughest water in Jul | Roughest water in Aug | Roughest water in Sep | Roughest water in Oct | Roughest water in Nov | Roughest water in Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Mixed | Mixed | Mixed | Calm | Calm | Calm | Mixed | Mixed | Mixed | Rough | Mixed | Rough |
Typical seasonal pattern, not a forecast. Any month can deliver a calm crossing or a bad one. Check the marine forecast for your sailing date. Select a month to see every sea and ferry crossing ranked for it.
Where to be on board
Front to back
- Bow (front)Avoid
- MidshipBest
- Stern (aft)OK
The crossing: 50 minutes to 25 hours
Roughest stretch: The open legs between the Amami islands, mostly overnight
Stay low and near the middle of the ship, away from the bow.
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The crossings that cross it
| Route | Typical duration | What to know |
|---|---|---|
| Kagoshima to Naha via Amami, Tokunoshima, Okinoerabu, Yoron and Motobu | about 25 hours | Marix Line's example timetable for 20 to 21 October 2026 has it leaving Kagoshima at 18:00 and reaching Naha at 19:00 the next day. A-Line serves the same ports. |
| Naha to Zamami (Kerama Islands) | 50 minutes by high-speed boat, about 2 hours by ferry | Queen Zamami leaves Naha Tomari at 09:00 and reaches Zamami at 09:50 in the 1 to 19 October timetable, and is in dock from 20 October to 3 December. Ferry Zamami leaves at 10:00 and reaches Zamami at 12:00. |
What helps on this crossing
- Read the operator's status board before you leave. Marix Line shows conditional operation, and A-Line posts port changes for rough seas on the day.
- On the Kagoshima run, expect port changes. Marix Line says a port change or a conditional destination may not be settled until just before sailing.
- For a short trip, take the 50 minute Queen Zamami from Naha, except from 20 October to 3 December 2026, when it is in dock. The operator says schedule changes or cancellations can be decided because of rough sea conditions, so check for updates before you go.
For the full toolkit see the seasickness guide, or what to do once it has already started. For what the trials actually say about the oldest trick on that list, see the verdict on looking at the horizon. If the rocking follows you ashore afterwards, that is land sickness, which is normal, and it passes.
Frequently asked questions
Is the East China Sea rough in October?
October is one of the roughest months in the data. Near Amami it is the highest, with 36% of days above the annual 75th percentile, and near Okinawa it reaches 32%, with December higher at 43%. The mean daily maximum wave height is about 2.0 m near Amami and about 1.6 m near Okinawa. A-Line says weather and sea conditions change with typhoons and fronts.
Is the East China Sea rough in May?
May is among the calmest months, with about 1.4 m mean daily maximum wave height near Amami and 1.1 m near Okinawa. About 12% of May days are above the annual 75th percentile near Amami and 8% near Okinawa.
Is the East China Sea rough in January?
January is moderate: 25% of days are above the annual 75th percentile near Amami and 36% near Okinawa.
How long is the ferry from Kagoshima to Naha?
About 25 hours on Marix Line's example timetable for 20 to 21 October 2026, leaving Kagoshima at 18:00 and reaching Naha at 19:00 the next day. It calls at Amami Oshima, Tokunoshima, Okinoerabu, Yoron and Motobu on the way.
Other crossings
Sources & further reading
- https://en.wikipedia.org/wiki/East_China_Sea
- https://en.wikipedia.org/wiki/Amami_%C5%8Cshima
- https://marixline.com/
- https://marixline.com/price_schedule/
- https://www.aline-ferry.com/status/status-route/route-kagoshima
- https://www.vill.zamami.okinawa.jp/ship/
- https://open-meteo.com/en/docs/marine-weather-api
Sea conditions described here are typical patterns drawn from published marine and operator information as of July 2026, not a forecast: conditions on any given sailing depend on the weather that day, and any month can deliver a calm crossing or a bad one. Route and operator names are trademarks of their respective owners; Dizzout is not affiliated with or endorsed by them. Seasickness sensitivity varies from person to person; this page is informational and not medical advice.