Tides are sea-level changes strongly influenced by differences in the Moon’s gravitational pull across Earth, with the Sun also contributing. Many places have about two high and two low tides per lunar day, but local geography changes the pattern. Use the supplied local record. Tidal range equals high-tide height minus the associated low-tide height.
Near new and full Moon, Sun, Earth and Moon are roughly aligned, producing larger ranges called spring tides. Spring means the tidal pattern, not the season. Near quarter Moons, solar and lunar directions are roughly at right angles, producing smaller neap-tide ranges. Weather can also affect actual sea level.
Example 1
High tide is 2.1m and the associated low tide is 0.6m. Find the range.
2.1−0.6=1.5m. The range is a difference, not the high-tide height alone.
Example 2
Which tidal pattern is expected near full Moon?
A spring tide with a relatively larger range, because the solar and lunar tidal effects are aligned.
Watch out: Spring tides occur near new and full Moon throughout the year.