Okinawa

Okinawa Prefecture spans the Ryukyu Islands — a 1,200-kilometre arc of coral islands running southwest from the tip of Kyushu toward Taiwan. The chain sits at the boundary of the East China Sea and the Pacific, and the islands' ecology, culture, and tidal character are each shaped by that position. The tidal regime is mixed semidiurnal: two unequal highs and two unequal lows each day, with diurnal inequality that means one of the two daily low tides is often notably lower than the other. Mean tidal range runs from about 1.2 metres at the outer islands (Miyakojima) to 1.7 metres at Ishigaki in the far south. Naha, the main city on the largest island, sits around 1.5 metres mean range. The consequence for the Ryukyus is ecological: tide drives access to the coral reef flats that ring most islands. At low water, reef platforms that are submerged for most of the tidal cycle emerge — shallow enough to walk in some places, rich enough in marine life to make reef flat observation one of the defining activities of the islands. The Yabiji reef at Miyakojima is the extreme case: a 7 km² reef platform that is fully accessible on foot only during the lowest spring tides of the year, a few times annually, when tide levels drop far enough to expose it. Naha anchors the chain with Shuri Castle, the reconstructed palace of the Ryukyu Kingdom (founded 1429, UNESCO World Heritage; the main hall burned in 2019 and restoration is ongoing as of 2025). The older city sits inland from the working port of Naha, which handles inter-island ferries as well as cruise traffic. To the south, Ishigaki is the gateway to the Yaeyama Islands, with Kabira Bay — known for glass-bottom boat tours and black pearl farming — and nearby Taketomi Island accessible by ferry. Throughout the chain, tide-aware planning is the default for reef snorkelling, kayaking, and fishing, because the difference between low water and high water over a coral reef flat can mean the difference between 0.1 metres and 1.5 metres of water over the reef crest. Tide predictions on pages in this region are from Open-Meteo Marine (±45 min / ±0.2–0.3 m) with JMA as the authoritative regional reference at jma.go.jp.