About our charts

We want you to know exactly what a Painted Shores chart is, and what it is not.

What is computed

Every height on the plate is the sum of the harmonic constants NOAA publishes for that station: up to 37 constituents, each an amplitude and a phase lag measured from years of the station’s own gauge record. We apply the standard nodal corrections for the year and sum the cosines for every quarter hour. The highs and lows are found by sign change in the rate, then refined. The method is the one in every published tide table; the margin prints the station number and the count of constants so the result is verifiable, not decorative.

Heights are above mean lower low water, the datum NOAA uses for its own tables. Times are in the station’s local time, daylight saving included. The on-screen preview and the printed file are computed by the same code; nothing is approximated for speed and then recomputed for print.

What the chart cannot know

The astronomical tide is a prediction, not a forecast. Wind, barometric pressure, river discharge and storm surge raise or lower the real water by amounts the harmonic method does not contain, sometimes by feet. A chart is a portrait of the year’s tide, not an instrument: never use it for navigation, anchoring, wading, or any decision where the real water level matters. Use NOAA’s own predictions and observations for that.

Which shores

We draw 61 NOAA stations, listed on the stations page. We never interpolate between stations or offer a “nearest” gauge under another town’s name: a chart is of its station, and says so.

Credits

Harmonic constants: NOAA Center for Operational Oceanographic Products and Services (CO-OPS), public domain. Flags: Wikimedia Commons, each file public domain by its own record. Photographs: generated for this studio with OpenAI image models, and said so on the plate where one is used.