Twice a day the Hudson at Hoboken runs upriver, then turns and runs back down to the sea. Here it is a tidal estuary, where river and ocean meet.
The current here often runs as fast as a paddler cruises, and it can push you toward piers, moored boats and ferry paths without warning. Always paddle with others and with someone experienced, and check the NOAA tide and current predictions and the marine forecast. Nothing on this page is a safety clearance.
Hoboken Cove, looking east toward Midtown. Press play and watch the tide climb the beach and the current turn around. Pick any date.
Watch the sunrise point shift through the year. Around the equinoxes in March and September the sun rises almost due east, which is where the Empire State Building stands in this view. In midwinter it rises well to the right of it, and in midsummer to the left.
A model, not a forecast. Built from the tide constants NOAA publishes, so it works for any date, but it leaves out wind, heavy rain and storm surge, which can move the real water by several feet. Check NOAA tide and current predictions for real plans.
The water level and current are calculated in your browser from the harmonic constants NOAA publishes for The Battery (adjusted to Weehawken) and for the Hudson at Pier 92, about 6 feet down: the same inputs NOAA uses for its own predictions. Checked against NOAA, they match within a few hundredths of a foot and knot, and high and low water within a few minutes. The sun position is calculated from the date; the camera angle is estimated from the photo, which was taken at a very low tide. The flow streaks move faster than the real current so that you can see them.
The tide reaches about 150 miles upriver, to the dam at Troy. Pick a place on the river, change the tide strength and the river flow, and watch water level and current fall out of step.
Teaching model. Placeholder values and simplified physics: speeds and times here are not predictions.
Model assumptions: a tide of about 4.5 ft range at the Battery scaled by the tide strength slider; peak tidal current 1.8 knots at the Battery, falling toward 65% at Albany; river drift scaled up toward the head of tide; high water travelling at about 34 km per hour; slack water lagging high water by about 3 hours, so slack falls near mid-tide when the lag follows distance. These are teaching values, not NOAA data. The lag and the salt front are the least certain parts.
An estuary is where a river meets the sea and the two mix. Fresh water runs down from the Adirondacks. Salt water comes in from the Atlantic through New York Harbor. The Hudson is tidal all the way up to the Federal Dam at Troy, about 153 river miles from the Battery. The name is often translated from the Mohican as "the river that flows both ways".
Twice a day the river really does run upstream, and then it runs back down. At Hoboken the flood runs toward the north-northeast and the ebb toward the south-southwest.
The ocean tide enters through the harbor as a long wave, hundreds of kilometres between crests. As it moves upriver it lifts the water surface, and that rising and falling surface is the tide. The current is the water moving to let the surface rise and fall. Tide height and current are related, but they peak at different times.
In a wave that only travels, like a ripple crossing a pond, the current is strongest at the crest and trough, so slack water falls at mid-tide. In a wave that bounces back and forth, like water sloshing in a bath, the current is strongest at mid-tide and slack at high and low water. An estuary is a mix of the two, and how much of each depends on where you are. The result is a lag: the current keeps running for a while after high or low water. The explorer above lets you change that lag.
The tidal wave travels at roughly the square root of gravity times depth, about 30 to 35 kilometres an hour in the deep channel. So high water reaches Hoboken soon after the Battery, but reaches Albany hours later. By then it is already time for the next low tide downriver. Slack water follows the same delay, which is why a tide table for one place cannot be used for another.
Around new and full moon the sun and moon pull together and the tide range grows, called spring tides. At the quarter moons they partly cancel and the range shrinks, called neap tides. Currents scale with it, so the same place can run noticeably faster a few days apart.
The river is always draining toward the sea. That adds a steady seaward push on top of the tide, so the ebb runs longer and faster than the flood, and the flood is shorter and weaker. After heavy rain or in the spring snowmelt the effect is stronger. In a dry spell it fades, and salt water reaches farther upriver.
Salt water is denser than fresh water, so it tends to creep upstream along the bottom while fresh water slides seaward on top. That means current can differ with depth, and a prediction for one depth does not match the surface. NOAA's station used by this project reports current at a 6 foot depth, which is close to what a paddler feels.
A tide table assumes average weather. Strong winds, storms and changes in air pressure can raise or lower the water and shift the timing. Always check current conditions and not just the table.
The tide and current decide when the water moves and which way. From here, pick the kind of ride you are curious about.
Ferry and boat waves, the short rideDownwind waves, the long ride