The Coast That Rings

The same moon pulls the whole eastern seaboard at once — Key West and Eastport feel the identical tug. Yet the height that tug raises the sea grows almost fifteenfold from one end of the coast to the other. And it does not climb steadily with latitude, the way you'd guess. It stays a shrug for two thousand kilometres of Florida and Carolina shore — then the Gulf of Maine rings like a struck bowl, and the tide triples in the space of a few hundred miles. Thirteen tide gauges, all on one shared ruler, read live from NOAA. Press play and watch the north end heave while the south barely breathes.

Every gauge is fed by the same astronomy. The moon and sun raise a bulge in the open ocean that is modest — a metre or so — almost everywhere on Earth. What you see in these columns is not the ocean tide. It is what each coastline does to it. A wide, gently sloping continental shelf piles the wave up as it shoals; a bay of the right length and depth catches the tide and sloshes it back and forth in step, amplifying it the way a child pumps a swing. The Gulf of Maine and the Bay of Fundy behind it form a basin whose natural rocking period sits right next to the tide's twice-daily beat. So it resonates — and the resonance is what raises Eastport's water by more than five metres while Key West stirs by less than half of one.

The far right column, Eastport, is only the doorway. Push through it into the Bay of Fundy proper and the funnel tightens until, at its head, the tide reaches sixteen metres — a five-storey wall of water twice a day, the largest tide on the planet. That figure runs clean off the top of this chart. Notice too that the climb isn't tidy: Georgia's wide shelf throws up its own local bump near Savannah, and the mid-Atlantic gauges from New Jersey to Rhode Island wobble around a metre with no clear trend. Tidal range is a conversation between the moon and the exact shape of the seabed — and the seabed has the last word.

How this was built. Predicted tide heights for thirteen NOAA / CO-OPS stations along the US Atlantic coast, from Key West to Eastport, hourly across one operating day in GMT, referenced to mean sea level — pulled from the public NOAA Tides & Currents prediction service. The range for each gauge is the highest predicted height minus the lowest over the day; because it is sampled hourly, a true astronomical extreme falling between samples is clipped by a few percent, so these are honest lower bounds on the real range. Columns are placed south-to-north by latitude, not by true coastal distance, and drawn on a single shared metre-scale so amplitudes compare directly. The amplification factor is the largest range divided by the smallest. The sixteen-metre Bay of Fundy figure is the well-established maximum at Burntcoat Head, not part of this feed. Snapshot refreshed periodically; predicted tides are stable.