Massachusetts

Massachusetts runs the New England tide story at full volume. From Buzzards Bay around Cape Cod to Boston Harbor and on up to Cape Ann, the open Atlantic pushes a moderately large semidiurnal tide into a coastline that funnels and amplifies it. Boston Inner Harbor sees a mean range close to 2.9 metres, climbing past 3.4 on spring tides; that is roughly twice the swing at New York Harbor and four times what San Diego runs. The pattern is two highs and two lows of comparable size, twelve and a half hours apart. Lowest lows around new and full moons open the flats off Quincy, Hull, and the Boston Harbor Islands for hours, and Cape Cod's bay-side beaches widen by tens of metres at the bottom of the cycle. Nor'easters stack water above predicted levels by 30 cm or more when they coincide with spring tide and onshore wind. The harmonic predictions on this site assume normal weather; for live coastal-flood threats, the National Weather Service Boston office is the authoritative source.