The availability of good harmonic constituent data varies from country to country, resulting in very different tide predeictions depending on what products you use. Within the United States, NOAA provides excellent harmonic constituents for free, but internationally it is a different story.
We first observed these challenges in Gulfo Nuevo in Argentina. The gulf is very deep, with a narrow mouth to the Atlantic and sloping benthic profile. As a result, the difference between high and low tides is consistently 5 meters or more. Various websites and products we used had different levels of accuracy when predicting the tides. We found one that was just predicting tides from a station over 200km away, outside the gulf, and therefore completely different in terms of water level and timing.
The various surf or weather report apps either use old data, or base large areas of coastline on one station. Many people are still using pre-2004 data published in Xtide's Harmbase. Harmbase is great, but it's data is locked in binary files and SQL, and the maintainer has given up on maintaining it outside the US .
All constituent data is delivered in Meters.
Much effort has been made to cover the requirements from libTCD.
If you have at least a year of hourly water level observations, you can convert those to harmonic constituents and submit them to this database online with a simple form.
Your submission will be automatically converted to a Pull Request to this repository.