Planning Dive Trips Around Japan's Typhoon & Rainy Season — Monthly Data Guide
2026-03-11
Plan dive trips avoiding Japan's typhoons and rainy season. Data: rainy season visibility is fine. Post-typhoon: 1-week recovery.
"Should I Avoid Typhoon Season and the Rainy Season?" — Data Answers
Common advice says to avoid Japan's rainy season and typhoon season for diving. But 46,000 real observations tell a different story:
- Rainy season (Jun–Jul): Virtually no impact on visibility. Yonaguni June average: 24.4m — essentially the same as May (24.2m).
- Post-typhoon: Lowest point is 2–4 days after passage.Recovery takes about 1 week.Exception: Yonaguni often improves after typhoons.
Monthly Risk Calendar
| Month | Typhoon | Rainy Season | Risk | Diving Assessment |
|---|---|---|---|---|
| Jan | None | None | ◎ Best | Best. Zero weather risk. Izu winter peak clarity. |
| Feb | None | None | ◎ Best | Excellent. Winter clarity at its best. |
| Mar | None | None | ○ Good | Good. No weather risk, but Izu spring bloom starting. |
| Apr | None | None | ○ Good | Good. Okinawa best season. Izu spring bloom. |
| May | Rare (1–2) | None (Okinawa only) | ○ Good | Good. GW period. Okinawa rainy but visibility unaffected. |
| Jun | Low (2–3) | Honshu rainy season (from early Jun) | ○ Good | Good despite myth. Rainy season doesn't reduce visibility. Low typhoon risk. |
| Jul | Moderate (3–4) | Rainy season ends (late Jul) | △ Caution | Caution. Increasing typhoon risk. Okinawa summer clarity begins. |
| Aug | High (4–5) | None | ▲ High Risk | High typhoon risk. Peak clarity (Yonaguni 26.5m) but 1-week recovery after hits. |
| Sep | Peak (5–6) | None | ✕ Peak Risk | Highest risk. But also Japan's clearest month (Yonaguni 27.3m). Target early September. |
| Oct | Moderate–High (3–4) | None | ▲ High Risk | Still some typhoon risk. Okinawa still excellent (26.8m). Late October more stable. |
| Nov | Low (1) | None | ○ Good | Good. Typhoon risk sharply drops. Izu recovering, Okinawa stable. |
| Dec | None | None | ◎ Best | Excellent. Zero typhoon/rain risk. Izu winter clarity begins. |
Is Rainy Season Really Fine for Diving?
The data clearly says yes. Rainfall barely affects open-water visibility because:
- Dive sites are typically on rocky reefs or offshore — land runoff doesn't reach them
- Visibility is driven by plankton density and swell conditions, not rainfall
- Data: IOP June = 11.3m vs May = 10.6m (June is actually higher)
The real rainy-season risk is trip cancellation from strong winds and rain, not poor underwater visibility. Boat cancellations are actually less frequent in rainy season than during post-typhoon typhoon season.
Post-Typhoon Visibility Recovery
| Time After Typhoon | Avg Change vs. Pre-Typhoon |
|---|---|
| Typhoon day | -3.2m |
| Day +1 | -4.1m |
| Day +3 | -3.8m |
| Day +5 | -2.1m |
| Day +7 (1 week) | -0.8m |
| Day +10 | -0.3m |
Lowest point: 1–3 days post-typhoon (avg −4.1m). Recovery to within −0.8m by day 7; essentially normal by day 10. Strategy: book trips 7–10 days after a typhoon passage.
Best Strategies
Option 1: Early September in Okinawa
Peak typhoon season, but early September has relatively typhoon-free windows. Yonaguni September average: 27.3m — Japan's annual peak. Best risk/reward ratio.
Option 2: Late October – November in Okinawa
Typhoon risk drops sharply in November (~1 per year average). Yonaguni still at 24.4m. Much lower cancellation risk with still-excellent clarity.
Option 3: January–February in Izu
Zero typhoon and rainy season risk. Izu's annual clarity peak (IOP 18.6m, Ito 18.8m). Cold water (~16°C) requires drysuit.
Option 4: April–May in Okinawa (Golden Week)
Pre-typhoon season, low weather risk. Ishigaki April–May is its clearest period (21–22m). Manta season. 1–2 average typhoons, so not zero risk.
Summary
- Rainy season (Jun–Jul) does NOT reduce visibility — the myth is debunked by data
- Peak typhoon risk: September (5–6 avg). Lowest: December–February (zero)
- Post-typhoon recovery: ~1 week — target 7–10 days after passage
- Yonaguni often improves after typhoons — a counterintuitive strategy for the bold
- Best risk/clarity balance: early September Okinawa, November Okinawa, or Jan–Feb Izu
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