The highest tides on Earth, live. How high the water stands across the bay and how fast it is moving, hour by hour. Tap the water, or a gauge.
The bay is a long funnel, and the water in it has a natural slosh: about 13 hours to run up to the head and back. The ocean's main tide repeats every 12 hours 25 minutes. Because those are so close, each tide arrives just in time to push the slosh higher, the way you time pushes on a swing. The funnel narrows and shoals toward Minas Basin, which squeezes the rise taller still.
Twice a day around 100 billion tonnes of seawater run in and back out, more than every river on Earth carries in the same time. The panel above works that number out live from the model, for the tide on screen.
At the head of the bay the incoming tide can arrive as a single wave running upriver: the tidal bore. The Canadian Hydrographic Service predicts it for Truro, Maitland and a few other rivers.
The colour and the moving lines come from NOAA's Gulf of Maine Operational Forecast System, a model that divides the gulf into cells about 700 m across and runs four times a day. The page reads the surface water level and surface current for the bay straight from NOAA's files. The last 6 hours are nowcasts driven by observed weather; the rest is the forecast. It is a model, not a measurement.
The gauges are the Canadian Hydrographic Service's official tide predictions, in metres above chart datum, roughly the lowest tide of the year. Only Saint John has a live gauge today; when it reports, its measured level shows in its chart. Tap a gauge to see the model and the prediction side by side.
The model keeps every cell at least 10 m deep, so the mudflats that drain at low tide in Minas Basin and Chignecto Bay stay wet on this map. It also stops about 10 km short of Truro, and leaves out the Saint John River above the Reversing Falls and the Avon River. Those waters have no colour. On-screen line speed is compressed so the slow open bay still moves.