New York

New York's coastline runs from the south shore of Long Island around the harbour at the Battery and up the Hudson estuary into the Tappan Zee. The tide reaches the harbour mouth from the open Atlantic and pushes through the Narrows into the Upper Bay before splitting north up the Hudson and east through Hell Gate. Mean range at the Battery is about 1.4 metres, harbour-tempered and predictable, with currents through Hell Gate and the East River sharper than the swing implies. The pattern stays cleanly semidiurnal: two highs and two lows about twelve and a half hours apart. For ferry traffic it changes nothing; for paddlers crossing the main channel, fishers working the South Shore inlets, or shell-hunters on Long Island's bay flats, the timing matters. Nor'easter season runs autumn through spring, and easterly storm surge can stack a metre or more above predicted levels when the storm tracks coincide with spring tide. The 2012 Sandy peak ran 2.8 metres above the predicted level at the Battery; the harmonic predictions on this site assume normal weather.