Guam

Guam is the largest island in Micronesia and the southernmost of the Mariana Islands, sitting at 13.5°N in the western Pacific. It is a US territory with a permanent Chamorro population and a substantial US military presence. The island is 50 kilometres long and 14 kilometres wide, with a plateau of raised coral limestone in the north and rugged volcanic hills in the south. The western coast faces the Philippine Sea; the eastern coast faces the Pacific. The tidal regime is mixed semidiurnal with a spring range of 0.5–0.7 m at Apra Harbor. Two unequal highs and two unequal lows occur each day, with the diurnal inequality sometimes pronounced enough that one of the two daily lows is only 0.05–0.10 m below Chart Datum — effectively staying high — while the other drops to 0.3–0.4 m below. The specific higher-high and lower-low pattern shifts with the lunar cycle and moon declination, so the actual useful tidal planning window varies week to week. The reef flat that fringes much of Guam's coastline is the main beneficiary of tidal planning. At low water, the reef flat inside the fringing reef can be as shallow as 0.1–0.2 m — impassable to small boats, accessible on foot for shore anglers working the outer reef edge. At high water, the same flat has 0.5–0.7 m of cover — enough for a kayak drawing 0.15 m but not for a Boston whaler drawing 0.4 m. Tumon Bay's calm lagoon, sheltered by the barrier reef, is the main water-sports hub; Ritidian Point at the north tip has an exposed reef flat that yields excellent low-tide shore fishing; Hagåtña faces Apra Harbor and the calmer western lagoon. Typhoon season runs June through November. Guam has taken direct hits from super typhoons, with central pressure below 900 hPa, and the island's storm-surge vulnerability on the western coast is well documented. Outside typhoon season, trade winds from the NE-E at 10–18 knots are reliable and make the western coast's reef-enclosed lagoons a consistent flat-water paddling environment.