Java

Java presents three distinct coastal characters depending on which shore you're on. The southern coast faces the open Indian Ocean, exposed to long-period southerly swells and subject to mixed semidiurnal tides with a mean range around 1.5 m at Chart Datum (Pelabuhan Ratu area). The northern shore borders the shallow Java Sea, where tidal ranges drop sharply — Karimunjawa records roughly 0.6 m mean range, with a more diurnal character. The eastern tip narrows into the Bali Strait, just 2.4 km wide at its narrowest point, where tidal currents run 2–3 knots as water moves between the Indian Ocean and the Java Sea. Karimunjawa, a national marine park roughly 90 km north of Semarang, operates as an archipelago of 27 islands and islets. The low tidal range keeps reef structures submerged and accessible for much of the day, which is why the park sustains healthy coral cover and is accessible by fast boat from Jepara or by scheduled ferry. At the eastern end, Banyuwangi sits at the Java side of the Bali Strait. The strait's tidal hydraulics are significant for mariners: current direction reverses with each tidal cycle, and timing crossings to the Bali side requires reading both tidal state and current set. The wider region draws visitors for the Ijen volcano complex, 50 km inland, where a sulphuric crater lake and a blue-flame phenomenon visible in pre-dawn conditions have made Banyuwangi a staging point for that trek. BMKG (Badan Meteorologi, Klimatologi, dan Geofisika) is the authoritative source for Indonesian tidal data, including predictions for all Java stations.