The day’s water
High and low water
| Time | Height |
|---|
Depth and clearance
Charted depths are below datum and the tide adds to them. Charted bridge clearances are above HAT and the tide takes them away. Leave a box empty to skip that part.
Sun and moon
A low-precision series: a rising or a setting to a minute or two. For a sight, use celnav.
Show it as the terminal does
A tide cannot be computed from a position. It depends on the shape of the coast and the depth and resonance of the basin, so every place needs constants somebody measured there. You pick a station, not a place — and the nearest one in a straight line can be on the wrong side of a headland.
Search by name
Every word has to appear somewhere in the name, the region or the country, in any order and anywhere inside a word, so lon new finds New London. Type any of ^ $ . [ ] | ( ) * + ? { } and it is used as a regular expression instead.
Nearest to a position
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What this is
Harmonic tide prediction from constants measured at 8,334 stations. It runs entirely in the browser with no network, which is the point: a tide table is worth most where there is no signal.
The synthesis follows Foreman, as carried by UTide — 70 constituents with their satellite modulations and shallow-water terms. The same engine runs in the POSIX awk version of this tool; the browser build is checked against it over hundreds of thousands of values, and agrees to the last bit or two.
Reference and subordinate stations
A reference station has harmonic constants measured there, and its curve is a real synthesis.
A subordinate station has no constants of its own. It carries time and height corrections to a reference station, which is how a paper tide table has always worked. For those, the high and low waters are the reference’s turns corrected, and the curve between them is drawn as a half cosine. There is no honest way to synthesise a continuous curve out of offsets, so this build does not pretend to.
Times, datums and what is missing
Times are the station’s own standard time — no summer time, exactly like a printed tide table. The datum is named on the day’s screen; heights are above it.
Nothing here knows about the weather. A deep low or a hard onshore blow moves the real water by a half metre or more, and a river in flood moves it further. Harmonics predict the astronomical tide and nothing else.
Where the data comes from
Assembled from neaps/tide-database (CC BY 4.0). NOAA harmonics are public domain; TICON-4 harmonics are CC BY 4.0.
Offline
Checking…
A training and cross-checking aid, not a substitute for judgement. Where this and the published tide tables for the port differ, the published tables are right and this is wrong.