# 潮の時間 — 満ちて、引いて

> Unofficial tide reference. This is not an official publication, meteorological authority, tourism authority, or booking service.

- Subject: The rhythm of the tide in the Yaeyama Islands (Okinawa), and where to find the exact high- and low-tide times
- Area: Yaeyama, Okinawa Prefecture, Japan
- Role: Convey the tide as another of the island's clocks — the roughly twice-daily rise and fall and its general link to the moon — while routing readers to the official tide table for exact times
- Verified: 2026-07-19
- Relationship: Independent project; not affiliated with or approved by the Japan Meteorological Agency, Taketomi Town, any tourism association, cited media, or public authorities
- Language: HTML page is Japanese (canonical) with an 8-language UI layer (ja/en/zh/ko/fr/ru/id/ms via ?lang=); this file and the JSON context are written in English by design, for machine consumption

## Use for

- Understanding that the Yaeyama sea rises and falls roughly twice a day (semidiurnal tide)
- Seeing today's predicted high- and low-tide times for the Ishigaki tide station (shown when the JMA tide-table data is available; an astronomical prediction, not each island's exact time)
- Understanding the general astronomy: the tidal range is larger ("spring tides") near new and full moon, smaller ("neap tides") near the half moons
- Knowing the exact high- and low-tide times are published by the Japan Meteorological Agency as the tide table for Ishigaki (an astronomical prediction; the real level shifts with typhoons, air pressure and wind)
- Knowing that at Nakamoto Beach (Kuroshima) the reef interior becomes like a natural pool at low tide, that the swim window is about two hours around low tide with a life jacket advised, and that depths, currents and the returning tide remain hazards
- Navigating to the JMA tide table, the tourism/travel sources, the island guides, and UMI YAIMA COMPASS

## Do not use for

Authoritative confirmation of tide times, exact times for an island other than the Ishigaki tide station, tide heights in centimetres, or whether a specific date is a spring or neap tide. The page shows only today's predicted Ishigaki times (an astronomical prediction, drawn from the official table); tide heights and specific-day spring/neap designations do not appear, by design, and it does not recommend walking on or swimming at any specific reef. For exact and up-to-date times, and for any day other than today, use the official JMA tide table for Ishigaki at the time of travel, remembering it is an astronomical prediction.

## Verified context

- The sea rises and falls roughly twice a day — semidiurnal tide (general tidal description; JMA tide table for Ishigaki).
- The tidal range is larger near the new and full moon ("spring tides") and smaller near the half moons ("neap tides") — general astronomical relationship; no specific date is designated (JMA tide table for Ishigaki).
- The exact high- and low-tide times are published by the JMA as the Ishigaki tide table; it is an astronomical prediction and the actual level shifts with typhoons, air pressure and wind.
- The swim window at Nakamoto Beach (Kuroshima) is about two hours around low tide, with a life jacket advised (Taketomi Town Tourism Association).
- At low tide, the reef interior at Nakamoto Beach becomes like a natural pool (Okinawa Story).

## Editorial scope

The rhythm of the tide and its relationship to the moon are stated as general astronomy, not as claims about any specific day. The page shows today's predicted high- and low-tide times for the Ishigaki tide station, drawn straight from the JMA tide table (baked into a same-origin file at deploy time; the page never computes or estimates times, and silently falls back to linking the official table when the data is unavailable). The Nakamoto Beach facts are sourced from the Taketomi Town Tourism Association and Okinawa Story. No tide height (cm) or specific-day spring/neap designation appears anywhere on the page; the only clock times shown are today's official Ishigaki prediction.

## Resources

- Machine-readable context: ./ai-context.json
- Discovery service: ../
- Island Time series: ../koro/ (routes), ../koyomi/ (calendar), ../ame/ (rain), ../yoru/ (night)
- Island guides: ../taketomi/, ../iriomote/, ../kohama/, ../hateruma/, ../kuroshima/
- JMA tide table (Ishigaki tide station / astronomical prediction): https://www.data.jma.go.jp/kaiyou/db/tide/suisan/suisan.php?stn=IS
- Taketomi Town Tourism Association — Nakamoto Beach (swim window; life jacket): https://painusima.com/133/
- Okinawa Story — Kuroshima (the low-tide lagoon): https://www.okinawastory.jp/about/yaeyama_area/kuro