Why Tides Are More Dramatic in Some Parts of the World

Some coastlines see barely a foot of difference between high and low tide. Others, just a few hundred miles away, see tidal swings of 40 or 50 feet. The moon and sun are pulling on all of it equally — the difference comes almost entirely from local geography.

The basic pull is the same everywhere

Tides are driven by the gravitational pull of the moon, with a smaller contribution from the sun, both tugging on the ocean's water as the Earth rotates. In the open ocean, far from any coastline, this produces a fairly modest, consistent tidal range almost everywhere on the planet.

Why bays and funnels amplify it so much

The dramatic tidal ranges — the Bay of Fundy in Canada is the most famous example, with tides reaching close to 50 feet — happen when a bay's shape funnels incoming tidal water into a narrowing space. As the bay narrows, the same volume of water is forced into a smaller area, and the water level rises far more than it would along open coastline. Some bays are shaped in a way that resonates with the natural tidal rhythm, amplifying the effect even further.

Why open, unobstructed coastlines stay modest

A coastline with no bay, inlet, or funneling geography to concentrate the tide sees a much smaller range — often just a few feet — because the water has nowhere to be compressed into. This is why open, relatively straight coastlines tend to have modest, predictable tides while nearby estuaries and bays can swing dramatically more.

Why this matters for surfing specifically

A spot with a large tidal range can go from a completely different wave at low tide to an unrecognizable one at high tide, often within a few hours. A spot with a small tidal range stays much more consistent throughout the day. Knowing which category your local break falls into changes how much tide timing should factor into your planning.

For how tide actually reshapes a wave rather than just its timing, see How Tide Affects Wave Shape, Not Just Timing.