01 · Today · — · 50°30′N 1°02′W
The water is rising.
Reading the tide…
September
High and low water in harbour time. Heights in metres above chart datum, which is roughly the lowest the tide ever falls.
| Date | First | Second | Third | Fourth | Range |
|---|
Waxing gibbous, eleven days old.
The moon pulls the sea into two long bulges, one beneath it and one on the far side of the earth. Harrow Ness turns through both every day, which is why the water here comes in twice.
At new moon and full moon the sun and moon pull together and the tide runs high and hard. Those are springs. At the quarters they pull across each other and the tide goes slack and shallow. Those are neaps. Springs reach the Ness about a day and a half after the moon, which is how long the ocean takes to catch up.
Five waves make one tide.
Every tide table is a sum. The moon, the sun, the moon's uneven orbit and the tilt of both add sine waves at fixed periods to mean sea level. At Harrow Ness five of them account for nearly all the water. The last row is what the harbour sees, from midnight today through tomorrow.
The seabed, sounded.
Soundings in metres below chart datum. Contours at 2, 5, 10, 20 and 30 metres. The seabed is drawn from a fixed procedural field each time the page opens, so it is the same seabed every time and it is not a real one. Not for navigation.
Harrow Ness is not on any map.
Its coordinates fall in open water in the English Channel, a little south-east of the Isle of Wight. Its tide is a real harmonic model: five constituents with fixed amplitudes and phases, summed for whatever moment you open this page, on whatever day. The moon's age, the sun's rising and setting, the month's high and low waters and the seabed are all computed and drawn here, in the browser. There are no images on this page.
The page keeps the harbour's hours. Open it after sunset at the Ness and it turns to the night watch on its own.
One HTML file, September 2026
IBM Plex Mono, Bold Monday for IBM
Age of tide 36 h