Capital Region (Höfuðborgarsvæðið)

The Capital Region of Iceland — Höfuðborgarsvæðið — wraps the south-western corner of the country around the harbour at Reykjavík, with the Reykjanes peninsula running south-west toward the Mid-Atlantic Ridge surface expression at Þingvellir, the long Faxaflói bay opening west to the open North Atlantic, and the geothermal coast running north toward Akranes. The tide here is the open North Atlantic signal modulated by the shallow shelf around Iceland: cleanly semidiurnal in pattern, two highs and two lows of comparable size each day, twelve and a half hours apart. Mean range at the Reykjavík harbour gauge is about 3.5 metres, climbing past 4.5 metres on the largest spring tides and dropping near 2.5 on neaps. That is a substantial swing for such a high-latitude open-coast position, and the harbour fishing fleet at the Old Harbour reads it for boat-launch windows on the rising flood. The defining seasonal feature is photoperiod — the midnight sun in June produces 21-hour twilight days when the solunar fishing windows extend through the night, and the December darkness around the winter solstice compresses solunar activity into a four-hour midday window. The Atlantic puffin colonies at Lundey across the bay, the geothermal beach at Nauthólsvík where hot-spring water mixes with the cold North Atlantic to produce an outdoor swimmable lagoon, the rocky intertidal at Grótta lighthouse, and the surf at Þorlákshöfn south of the Reykjanes peninsula all read the table for different windows. The Icelandic Coast Guard's Hydrographic Department (Sjómælingar Íslands) publishes the authoritative tide tables; Open-Meteo Marine drives the gridded predictions on this site. Storm surge from North Atlantic depressions in winter can lift water levels well above predicted.