A lunar day—the time it takes a place on Earth to rotate back beneath the Moon—is about 24 hours and 50 minutes. In an ideal semidiurnal pattern, that produces two high tides and two low tides during a lunar day, with high tides roughly 12 hours and 25 minutes apart. Real coastlines often depart from that simple timing.
Continents block the free movement of tidal waves, and every ocean basin has its own shape, depth, and natural response. Those effects create three broad patterns. Semidiurnal tides have two similar highs and two similar lows per lunar day. Mixed semidiurnal tides also have two highs and two lows, but their heights differ. Diurnal tides have one high and one low. Along North America these are regional tendencies—semidiurnal on much of the East Coast, mixed on much of the West Coast, and diurnal in parts of the Gulf of Mexico—not universal rules.
This is why tomorrow’s tides cannot be found by adding a fixed number of minutes to today’s. Tide Guide uses the prediction for the selected station so its local pattern, time zone, and reference datum stay together.
Source: NOAA Tides and Water Levels