Two high and two low tides each lunar day. The two highs and two lows are about the same height. These are found along the U.S. Atlantic coast. They are most commonly semidiurnal with a tidal period of 12 hours and 25 minutes, but they may have diurnal periods for a few days each month. They are common along the U.S. Pacific coast.
Tidal currents are negligible at high and low tides.
When the tide has reached its highest point, the current velocity is zero and this is called high slack water . When the following ebb current reaches zero velocity at low tide, this is called l ow slack water . This is largely due to the unique shape and configuration of the bay. Very high tides are also observed in some areas along the coast of France. Of particular interest is Mont St. Michel , where the small town is isolated at high tide, and where the tides come in faster than a person can walk.