Autumn Diving (Sep–Nov) Visibility in Japan: Heaven or Hell Depending on Where You Go

March 11, 2026 · 11 dive sites analyzed from real observation data

Autumn Diving in Japan: Completely Different Worlds by Region

Some say 'autumn is bad for diving,' while others insist 'autumn is the best.' Both are right and wrong — the answer is that autumn visibility follows completely different patterns by region. In Okinawa, September is the annual peak (Yonaguni 27.3m). In the Sea of Japan, Tajiri hits its annual low of 6.4m in October. We analyze data from 11 sites to reveal autumn diving's true character.

Autumn Trends by Region

★

Okinawa (Yonaguni)

Autumn is annual peak

27.3m in Sep is the annual peak. Oceanic water + post-typhoon clearing drives surge

Sep: 27.3mOct: 26.8mNov: 24.4m

↗

Izu Peninsula

Improving through autumn into winter

IOP improves +2m from Sep to Nov. Futo and Ito trend upward. Further gains through December

Sep: 12.7mOct: 13.7mNov: 14.7m

↘

Sea of Japan

Autumn is the worst (October)

Echizen, Aoumi, Tajiri hit annual lows in October. Autumn typhoons + westerlies drive turbidity

Sep: 9.4mOct: 7.5mNov: 8.5m

Site-by-Site Visibility Trend: Aug–Dec

Site	Region	Aug	Sep	Oct	Nov	Dec	Trend
Yonaguni	Okinawa	26.5m	27.3m	26.8m	24.4m	23.4m	★Autumn peak
Kerama	Okinawa	20.9m	19.8m	19.2m	19m	18.5m	↘Declining
IOP	Shizuoka	12.3m	12.7m	13.7m	14.7m	17.3m	↗Improving
Futo	Shizuoka	10.1m	10.7m	11.3m	12.5m	15m	↗Improving
Mikomoto	Shizuoka	12.7m	13.2m	12.9m	12.5m	13.7m	→Stable
Ito	Chiba	15m	14.7m	15.8m	15m	18.7m	↗Improving
Kashiwajima	Kochi	13m	13.9m	12.6m	14.1m	16.3m	↗Improving
Kushimoto	Wakayama	12.7m	11.5m	12.9m	11.6m	13.1m	→Stable
Echizen	Fukui	10.3m	10.3m	8.7m	—	—	↘Declining
Aoumi	Yamaguchi	10.6m	8.4m	7.5m	8.5m	9.3m	↘Declining
Tajiri	Tottori	12.4m	9.4m	6.4m	7.7m	9.7m	↘Declining

Okinawa: September Is the Annual Best

Yonaguni's September (27.3m) is the annual maximum, surpassing even August (26.5m). Oceanic water drawn in by typhoons and the subsequent clearing after typhoon passage combine to produce peak autumn clarity. Kerama declines slightly from September (19.8m) to November (19.0m) but remains stable near 20m throughout autumn. Sea turtle encounters remain high after the nesting season, making autumn one of Okinawa's best overall periods.

Izu Peninsula: Steadily Improving Through Autumn into Winter

IOP's visibility rises month by month from August (12.3m) to November (14.7m), then jumps further in December (17.3m). Futo shows the same pattern: August (10.1m) to December (15.0m) steady improvement. This is driven by declining plankton as summer water temperature peaks pass. In Izu, the counterintuitive rule is: the later in autumn you dive, the better the visibility. November–December marks the entry into Izu's best season.

Sea of Japan: Autumn Is Actually the Worst

Tajiri (Tottori) records just 6.4m in October — its annual minimum. Echizen (Fukui) also hits a low at 8.7m in October, and Aoumi (Yamaguchi) at 7.5m. The Sea of Japan's autumn is genuinely the worst period. Multiple factors contribute: approaching typhoons generating waves and turbidity, and the Sea of Japan's counterclockwise circulation concentrating turbid water on the coast. Divers planning Sea of Japan trips in autumn should take note.

Planning Autumn Diving?

Good Autumn Dive Areas

Yonaguni: 27.3m in Sep — annual peak
Kerama/Ishigaki: Stable 19–21m throughout autumn
IOP/Futo: Improving Oct–Dec
Ito (Chiba): Oct peak 15.8m, Dec 18.7m

Areas to Avoid in Autumn

Tajiri (Tottori): October 6.4m — annual low
Echizen (Fukui): October drops to 8.7m
Aoumi (Yamaguchi): Sep–Oct worst (7.5–8.4m)
※Sea of Japan: typhoons + westerlies make autumn worst

Summary

Talking about autumn diving requires knowing 'where.' In Okinawa, autumn (especially September) delivers the year's best visibility. Izu Peninsula uses autumn as a recovery period, improving rapidly through November–December. The Sea of Japan has its worst visibility in autumn, with October recording barely believable lows. Always check regional autumn characteristics when planning your trip.

Data source: scraped from public dive logs. Monthly averages.