Ishigaki Water Temperatures — Testing "Wetsuit All Winter" Against 4,665 Yaeyama Measurements
2026-03-09
"Can you really dive Ishigaki in a wetsuit in winter?" Yes — and we can back it with measurements. But "any thickness, any time" is not true, and this article is honest about where its numbers come from.
First, an honest note about the data
Our database holds 1,473 observations from Ishigaki — but only 12 of them include water temperature (our sources there focus on visibility; an earlier version of this article wrongly claimed "1,473 temperature records," which we hereby correct).
So this article leans on 4,665 measurements from Yonaguni (2007–2026) — an island in the same Yaeyama group, on the same upstream Kuroshio subtropical water. For water temperature purposes, they are the same sea.
The answer, by month
| Period | Measured mean | What the data says | Suit |
|---|---|---|---|
| Jan–Mar | 23.8–24.2°C | Floor of 22.0°C — no drysuit, guaranteed. But ~4 days in 10 read below 24°C | 5mm + hooded vest (3mm is a gamble) |
| Apr–May | 25.0–26.3°C | Sub-24°C days all but vanish | 5mm, then 3mm |
| Jun–Sep | 27.6–28.7°C | 9 days in 10 at 28°C+ (Jul–Sep) | 3mm / rashguard |
| Oct–Nov | 26.4–27.8°C | October still hits 28°C+ on 6 days in 10 | 3mm, then 5mm |
| Dec | 25.2°C | Only 5% of days below 24°C | 5mm |
Tune it to your own cold tolerance with the wetsuit thickness tool.
What "wetsuit all winter" actually means
- No drysuit needed — truly. Across 4,665 measurements, even February's floor is 22.0°C. Compare mainland Japan the same month: Futo on the Izu Peninsula averages 15.1°C — an 8.7°C gap — and dips below 16°C two days in three. Flying south in winter buys you exactly what the numbers promise.
- But a 3mm in midwinter is a gamble. In January–February, 4 days in 10 read below 24°C, and an hour in 24°C water will chill you. Winter's right answer is a 5mm with a hooded vest — a boat coat if you run cold (our thickness guide explains why).
- July–September are a dead heat (28.6–28.7°C, 28°C+ on 9 days in 10). Since water temperature won't differentiate the peak months, pick your dates by typhoon risk, crowds, and airfare instead.
Monthly temperature chart
About Ishigaki's own measurements
All 1,473 Ishigaki observations (mostly visibility) are browsable in the historical archive. Only 12 carry temperatures today; as temperature-bearing sources grow, we'll switch this article to direct data.
Note: Guidelines from measured distributions — your comfort, local shop advice, and equipment requirements come first.
Data sources
- Water temperatures: this site's database (Yonaguni, 4,665 readings, 2007–2026; Ishigaki 1,473 observations, 12 with temperature), browsable in the archive
- Regional conditions: JMA sea-surface temperature / Kuroshio Current
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