Transparency matters at a site famous for water. This page documents how MontSaintMichel.com generates tide predictions and where the model can be wrong.
What we are not
Our tide calendar and Visit Planner are not products of SHOM (Service hydrographique et océanographique de la marine) or any French official hydrographic office. Do not use them for navigation, pilotage, bay crossing, or legal compliance. For those purposes, use official French services.
What we are
We operate a self-calculated harmonic tide engine tuned for visitor planning at Mont-Saint-Michel. The pipeline:
- Data source: REFMAR gauge records for Saint-Malo, ingested and stored as our baseline astronomical signal for the bay region.
- Constituents: Harmonic constituents fitted from that series—standard tidal components (M2, S2, etc.) with local calibration.
- Prediction: Synthesis forward to produce high/low times and heights for calendar display.
- Calibration: Periodic comparison against independent observation sets and published tide tables; parameters adjusted when bias appears.
- Validation: Automated reports (see
tide_engine/in our repository) track error against held-out observations.
Known limitations
- Location offset: Saint-Malo gauge ≠ Mont-Saint-Michel esplanade; phase and height can differ by tens of minutes and decimetres on extreme coefficients.
- Weather surge: Harmonic models miss storm surge and atmospheric pressure effects.
- Esplanade flooding: Visitor "island effect" depends on coefficient, wind, and local bathymetry—treat our times as planning hints, not flood maps.
- Official changes: Channel works and silting evolve; we recalibrate when new REFMAR data arrives.
How we use predictions on the site
The tide calendar and Visit Planner suggest when to arrive for photography and abbey pairing. Our high tides guide explains coefficient spectacle vs bridge access myths.
Practical information elsewhere
Abbey hours, parking, and shuttles come from monument and public establishment sources—not from the tide engine. See visitor tips and directory.
Questions or spotted errors: info@travelust.com. Last methodology review: July 2026.