California

California's coastline runs from the Mexican border up past the Channel Islands and on to the Oregon line, and the tide signature changes more than the latitude suggests. Most of the coast reads mixed semidiurnal, two highs and two lows of unequal size each day, with the bigger swing falling on the lower-low water. San Diego sits inside a sheltered bay where the swing is calm and steady, around 1.7 metres at the harbour. North of Point Conception the open ocean pushes the range up and the timing back. The cleanest tidepool windows show up around new and full moons, when the lowest lows drop below MLLW and the inner shelf at Cabrillo or further up the coast at La Jolla opens for an hour or two either side. Surfers read the same tide table for a different reason: low water reshapes the breaks, and the change-of-tide rip is when the coast wakes up. Storm surge from a Pacific low can shift actual water level 10 to 20 cm above prediction in winter; the tables on this site assume calm.