Seasons and sky
Semidiurnal Tide
Direct answer
Semidiurnal Tide: A Semidiurnal Tide is a tidal pattern with two high waters and two low waters of roughly similar height during a lunar day.
A Semidiurnal Tide has two broadly similar highs and lows each lunar day.
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At a glance
- Found in
- Seasons & Earth Almanac
- Related
- Tidal Datum, Diurnal Tide, Astronomical Season, Equinox
A Semidiurnal Tide has two broadly similar highs and lows each lunar day.
A Sun-Earth orientation for seasonal, atmospheric, tidal, and terrestrial terms.
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The story behind Semidiurnal Tide
Harmonic analysis explained semidiurnal patterns through strong twice-daily lunar and solar constituents.
How to read Semidiurnal Tide
Semidiurnal Tide speaks to regional tide classification and local daily scheduling from an official station forecast.
Semidiurnal Tide in practice: an example
Many Atlantic coast locations show approximately twelve-hour spacing between successive high waters.
Where readings of Semidiurnal Tide go wrong
A common error is to assume exact equal heights or six-hour high-to-low intervals; local constituents and weather modify the curve.
Sources and editorial method
Research references used for this entry include:
- NOAA Tides and Currents Glossary - Operational definitions for tides, tidal currents, ranges, datums, bores, and amphidromic systems.
- Source
- The Great Almanac Dictionary
- Category
- Seasons & Earth Almanac
- Last updated
- 2026-09-26
Identify the twice-daily tide pattern
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Common questions
What is a Semidiurnal Tide?
A Semidiurnal Tide is a tidal pattern with two high waters and two low waters of roughly similar height during a lunar day.
What do people get wrong about a Semidiurnal Tide?
A common error is to assume exact equal heights or six-hour high-to-low intervals; local constituents and weather modify the curve.
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