Annual Visibility Calendar: Month × Region Matrix for Optimal Timing
2026-03-16
'Where should I dive next month for the best visibility?' This month × site visibility matrix answers at a glance. Built from 46,000+ real observations, it maps average visibility for every month and site. Bottom line: Yonaguni dominates year-round. For Honshu, winter IOP (18.6m) is the gold standard.
Month × Site Visibility Matrix (meters)
| Site | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| IOP | 18.6 | 17.5 | 12.8 | 10.2 | 8.5 | 7.2 | 7.8 | 10.5 | 12.7 | 14.8 | 16.5 | 18.2 |
| Futo | 16.8 | 15.2 | 11.5 | 9 | 7.8 | 6.5 | 7.2 | 9.8 | 11.2 | 13.5 | 15 | 16.5 |
| Echizen | - | - | - | 5.8 | 7.2 | 8.5 | 9.7 | 9.2 | 8.8 | 7.5 | - | - |
| Kushimoto | 12.5 | 12.8 | 10.5 | 9.2 | 8.5 | 8 | 9.5 | 10.2 | 11.5 | 12 | 12.5 | 13 |
| Kerama | 18.5 | 19 | 20.5 | 21 | 20.8 | 20.5 | 21.3 | 18.5 | 19.8 | 19.5 | 19 | 18.8 |
| Yonaguni | 23.5 | 24 | 25 | 25 | 24.5 | 23.8 | 24.2 | 24.8 | 27.3 | 25.5 | 24 | 23.2 |
| Hachijojima | 17.4 | 16.9 | 15.2 | 15 | 19.8 | - | 13.6 | 17.3 | 21.9 | 16.4 | 16.9 | 16.8 |
| Ito | 18.7 | 17.5 | 13.2 | 10.5 | 8.8 | 7.5 | 8.2 | 10.8 | 12.5 | 15 | 17 | 18.7 |
| Mikomoto | 15 | 14.5 | 11 | 8.5 | 7.5 | 8 | 9.5 | 11.8 | 13.2 | 14 | 15.5 | 16 |
| Hirasawa | 12.5 | 11.8 | 8.5 | 6.2 | 5.5 | 4.8 | 5.5 | 7.2 | 9.5 | 10.8 | 12 | 12.8 |
Three Patterns from the Matrix
Pattern 1: Honshu = Winter High, Summer Low
IOP, Futo, Ito, Mikomoto, Hirasawa all follow the same trend. January peaks (15–19m), June bottoms (5–8m). Spring plankton bloom and rainy season are the causes. Winter diving wins on visibility.
Pattern 2: Okinawa = Year-round Stable
Yonaguni (23–27m) and Kerama (18–21m) show minimal monthly variation. Good visibility anytime. Yonaguni's September 27.3m is the annual peak.
Pattern 3: April Is Tough Nationwide
Honshu spring bloom peaks. Every non-Okinawa site drops to around 10m. For April diving, Okinawa is the only choice. Yonaguni 25.0m, Kerama 21.0m.
Monthly Best Site Guide
IOP 18.6mRunner-up: Ito 18.7m
Winter Izu peaks in clarity. Water ~16°C, drysuit recommended.
Yonaguni 24mRunner-up: Kerama 19.0m
Hammerhead season begins. Okinawa stays at 20m+ even in winter.
Yonaguni 25mRunner-up: Kerama 20.5m
Honshu spring bloom begins. Okinawa is the safe choice.
Yonaguni 25mRunner-up: Kerama 21.0m
Peak spring bloom across Honshu. Okinawa is the only option.
Yonaguni 24.5mRunner-up: Hachijojima 19.8m
Golden Week: Hachijojima is a hidden gem. Honshu still recovering.
Yonaguni 23.8mRunner-up: Kerama 20.5m
Rainy season makes Honshu unstable. Okinawa's rainy season ends earlier.
Yonaguni 24.2mRunner-up: Kerama 21.3m
Echizen 9.7m is a Japan Sea option. Okinawa enters best season after rainy season.
Yonaguni 24.8mRunner-up: Kerama 18.5m
Obon crowds. Water temp peaks but Honshu visibility is lower.
Yonaguni 27.3mRunner-up: Hachijojima 21.9m
Silver Week target. Hachijojima at annual peak. Typhoon risk exists.
Yonaguni 25.5mRunner-up: Kerama 19.5m
Izu recovering (IOP 14.8m). Well-balanced month nationwide.
Yonaguni 24mRunner-up: Ito 17.0m
Izu enters winter clarity season. Water still in low 20s°C.
Yonaguni 23.2mRunner-up: Ito 18.7m
Year-end diving. IOP 18.2m is also good. Drysuit essential.
Summary: When to Go Where
Visibility priority
Yonaguni × September (27.3m) is the database maximum. For budget-conscious Honshu divers, winter IOP (18.6m) offers the best value.
Water temp matters too
For both visibility and warm water, Hachijojima in September (21.9m / 25.8°C) is ideal. Okinawa stays above 24°C year-round.
About the Data
Monthly averages from 46,483 observations across 42 sites (2006 – Mar 2026). Matrix shows 10 representative sites. Visibility is mean of daily min/max. Months with fewer than 50 observations are approximate.
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