Why Are Some Tides Bigger Than Others? One Coast Gets 30 Feet, the Next Gets Two
Why Are Some Tides Bigger Than Others? One Coast Gets 30 Feet, the Next Gets Two
For me, tide is everything. Wind matters more than rain — I check the wind before I check the sky. Trying to explain why to someone who has never fished feels like talking to myself.
Where I fish, the water can rise and fall by more than thirty feet between low tide and high. Say that number to someone fishing a different coast, and they'll think you're exaggerating.
They're not wrong to be suspicious. The Moon pulls on every ocean on Earth. So why does one coastline move thirty feet and another barely move at all?
An experienced American fisherman watches the exposed tidal flats at sunrise, carefully reading the tide before beginning a day of coastal fishing.
One Moon Pulls on Every Ocean. Why Doesn't Every Coast Get the Same Tide?
Here's the assumption almost everyone starts with: the Moon pulls the ocean toward it, the water bulges on that side, and that bulge is the tide. It's simple, tidy, and incomplete.
Tidal range — the vertical difference between a coastline's high tide and its low tide — is what varies so dramatically from place to place, and it depends mainly on the shape of the coastline itself, not on how hard the Moon happens to be pulling on a given day.
NOAA describes tides as long, ocean-spanning waves generated by the Moon, the Sun, and Earth's own rotation. The Moon's pull is doing more than most people assume — it sets that wave in motion across the whole planet. As the wave crosses an ocean basin, it hits continents, coastlines, and varying seafloor depths, growing in some places and shrinking in others.
That's the part the simple version leaves out. The Gulf of Maine is the case in point: the Bay of Fundy, long and narrow, has a natural sloshing rhythm that nearly matches the tide wave's timing — so instead of canceling out, the two reinforce each other and the water piles higher with every cycle.
Southern Florida's coastline doesn't share that resonance, so the same lunar and solar pull barely moves its water by comparison. It's the same principle behind a coastline like mine swinging past thirty feet while a fisherman two states over watches scarcely two.
Same Moon. Same math. A completely different ocean.
The bulge itself is also more complicated than the schoolbook drawing. Research from oceanographers Pugh and Woodworth, along with USGS's coastal tides overview, describes tidal bulges forming on both sides of Earth. It isn't that water gets pulled toward the Moon and away on the far side — it's that the Moon's gravity pulls unevenly across the whole planet, stretching the ocean at both ends.
NOAA's own tide education materials go further, pointing out that not every coast even gets two tides a day. Some get one dominant tide, some get two of noticeably different heights, and the pattern depends on the local coastline's resonance, not simply on where the Moon sits in the sky.
Here's the simplest way to put it: the Moon doesn't pull water toward itself so much as it stretches the whole ocean, and a coastline simply catches more or less of that stretch, depending on its shape. That's the science underneath a fisherman's water. The calendar tells you the Moon's position; the coastline tells you what it's going to do with it.
A bright full Moon shines over the Atlantic Ocean as moonlight reflects across the water, illustrating the Moon's role in creating ocean tides.
Spring Tide, Neap Tide, and the Geometry Behind the Swing
The shape and depth of the coastline decide the ceiling — what oceanographers call the basin's geometry. The Moon and Sun's alignment decides how close any given day gets to it.
Picture the Earth, Moon, and Sun lined up almost in a straight row — that happens near the new Moon and the full Moon. When it does, the Moon's pull and the Sun's pull add together, and the tide swings harder in both directions.
Sailors and oceanographers call this a spring tide — nothing to do with the season.
About a week later, the Moon sits at a right angle to that line instead. The Sun's pull now partly cancels the Moon's, and the swing flattens out into what's called a neap tide.
NOAA's monthly tide graphs show this rhythm almost like clockwork — the range widening near the new and full Moon, narrowing near the quarters, over and over, roughly every two weeks.
It's a pattern precise enough that the mathematician Doodson reduced it to a set of predictable harmonic components by 1921. That work eventually let mechanical tide-predicting machines forecast coastal water levels decades before satellites existed.
None of that math matters much standing on a dock. What matters is the calendar and the swing it points to — and every fisherman who's paid attention long enough already carries that calendar in their head, whether they'd call it geometry or not.
Powerful spring tide currents rush through a coastal inlet as the Sun and Moon align, creating one of the month's strongest tidal movements.
The Myth That Fishing Has Nothing to Do With Science
People who don't fish tend to picture it as sitting still, waiting. It isn't. It's a running data problem that coastal communities were solving long before anyone handed them an app or a satellite forecast.
Ask any charter captain today and the answer is the same: tide tables, wind direction, and a marine forecast app get checked before the boat ever leaves the dock — not out of curiosity, but because getting it wrong means a wasted trip, or worse.
Maybe that's the pattern across recreational fishing generally: local knowledge and scientific data were never really rivals. They just run together, whether anyone gives that combination a name or not.
Fishing looks like the opposite of science until you actually watch someone do it for a living.
That instinct for reading water didn't start with phone apps, either, and it wasn't distributed evenly. Indigenous communities in what's now British Columbia and Washington State spent generations learning exactly where the water would sit at each stage of the tide, then built rock-walled terraces at that precise height to maximize shellfish growth. A 2014 study published in PLoS ONE tested the result: those clam gardens produced roughly four times as many butter clams and twice as many littleneck clams as unmanaged beaches nearby. That kind of precision didn't come from an instrument. It came from watching the water for a very long time.
The same pattern keeps resurfacing in completely different centuries and completely different circumstances. On the Atlantic coast, generations later, that same tidal knowledge became something rarer: leverage. Historian Kevin Dawson's research on enslaved ship pilots, published in the Journal of Social History, describes how these pilots earned a strange kind of authority aboard the vessels they guided — resting almost entirely on their ability to read a channel's tide and current better than anyone else on deck, including the captain who legally owned them. At places like New York's Hell Gate, where Atlantic tidal forces and river currents collided into eddies and whirlpools, that skill wasn't a curiosity. It was the only thing standing between a ship and the reef.
The instruments changed. What people were doing with the water never really did.
That same thread runs straight into the present, just wearing a different shape: citizen-science flood monitoring. A platform called MyCoast now lets anglers, boaters, and anyone else on the water submit photos of flooded docks, streets, and shorelines during king tides and storm events, automatically tagged with weather and tide data. State agencies from Rhode Island to Washington use those crowdsourced photos to identify which spots flood first, feeding that stream directly into local coastal planning, alongside the tide gauges NOAA already runs.
It's hard not to read the pattern the same way across all of it — from a captain's phone app back to a clam garden built centuries before anyone had one: reading the water was always a kind of science, whether anyone called it that or not.
An American recreational fisherman checks NOAA tide charts and marine weather forecasts on a smartphone before launching his boat.
When the Calm Hobby Meets the Storm
The same skill that tells you when to launch the boat is the one that tells you when the water is about to become the story on the evening news.
Storm surge builds up largely on its own — wind and low pressure pushing water inland — but where it overlaps with the tide, the two compound. When Hurricane Sandy hit the New York and New Jersey coast in 2012, the storm surge arrived close to local high tide. NOAA and National Weather Service records showed water levels rising several feet above the normal high-water mark, turning ordinary flood zones into record ones.
The National Hurricane Center's technical report on Hurricane Katrina tells a related but different story along the Mississippi coast in 2005. There, storm surge reached 24 to 28 feet above normal tide levels in the hardest-hit stretch between Waveland and Pass Christian — driven mainly by the storm's enormous wind field and the shallow, gently sloping seafloor offshore, which let the surge pile up as it came ashore. The exact timing against the tide cycle mattered far less here than it did with Sandy. Some storms need the tide's cooperation to do their worst. Katrina barely needed to ask.
That makes Katrina the exception, not the rule. Most storms aren't so overwhelming that timing stops mattering. USGS's broader analyses of coastal storm surge describe the more common pattern up and down the coast: when a storm's peak surge does align with high tide, the combined water level — what forecasters call the storm tide — can run well beyond what either the surge or the tide would produce on its own.
There's something almost unfair about it: the same math that tells a fisherman when the water will be gentle is the math a hurricane borrows to be worse.
Storm surge floods an American coastal town during a hurricane at high tide, demonstrating how extreme weather and tides can combine.
| What's Moving the Water | What Drives It | How Predictable |
|---|---|---|
| Ordinary daily tide | Moon and Sun's pull, shaped by coastline and seafloor | Highly predictable, years in advance |
| Spring tide | Moon and Sun aligned in a nearly straight line | Predictable, roughly twice a month |
| Storm surge | Wind and low pressure pushing water inland during a storm | Forecast in real time, height depends on tide timing |
That's the pull of the Moon — the reason high tide and low tide never sit still. Slide the Sun in behind it, and the swing grows even more extreme.
Time that alignment with a hurricane, and a coastline can pay for it in ways that go far past a ruined afternoon of fishing.
Maybe that sounds like a small thing to track for a hobby. But reading what's actually pulling on the water — Moon, Sun, storm, coastline, all of it — might be the only thing that makes someone a fisherman, rather than just someone holding a rod.
An experienced American fisherman stands beneath a full Moon, reflecting on the connection between the Moon, the tides, and the ocean.
Frequently asked questions
Why are some tides bigger than others?
Tidal range depends mostly on a coastline's shape and depth, not just on how hard the Moon is pulling. Coastlines like the Bay of Fundy amplify the tidal wave because their shape matches its natural rhythm, while other coasts dampen it — which is why tidal range can differ enormously between two places under the same Moon.
What is the difference between a spring tide and a neap tide?
A spring tide happens when the Moon, Earth, and Sun are nearly aligned, near the new and full Moon, causing bigger swings between high and low water. A neap tide happens about a week later, when the Moon and Sun pull at roughly a right angle to each other, partly canceling out and producing a smaller swing.
Does a hurricane make high tide worse?
Yes — storm surge adds to whatever the normal tide is doing at the time, and when the two peaks align, as they did during Hurricane Sandy, the combined water level can run well past what either one would produce alone. Some hurricanes, like Katrina, are so large that the storm's own size and the shape of the seafloor matter more than the tide's exact timing — but the two are always stacking on top of each other in some proportion.
Do fishermen still use tide tables, or just apps?
Most rely on both. Charter fishing captains routinely check tide tables, wind forecasts, and marine current apps together, combining official data with local, experience-based knowledge of how a specific bay or inlet actually behaves.
Is climate change affecting tide patterns?
Rising sea levels are raising the baseline that ordinary tides work from, which NOAA and IPCC reports link to more frequent "sunny day" flooding in some coastal areas even without a storm. Citizen-science programs now use flood reports from boaters and anglers to help track these changes at the local level.
Why does the ocean bulge on both sides of Earth, not just the side facing the Moon?
The Moon's gravity pulls unevenly across the planet, stretching the ocean at both the near and far sides rather than simply dragging water toward itself. That uneven stretch is what produces two tidal bulges instead of one.
What is a "spring tide" — does it have anything to do with the season?
No — despite the name, a spring tide can happen in any season. It refers to the water "springing" higher during the Moon and Sun's alignment near new and full Moon phases, not to spring the season.
Sources & References
- NOAA, "What are tides?" (2024)
- NOAA, Tides and Water Levels education pages (2023–2024)
- NOAA, "Hurricane Sandy Water Levels" (2013)
- NOAA, Sea Level Rise Technical Report (2022)
- Pugh & Woodworth, Sea-Level Science, Cambridge University Press (2014)
- USGS, Coastal Tides Overview (2020) and Coastal Storm Surge Analyses (2015)
- National Hurricane Center, Tropical Cyclone Report: Katrina (2010)
- Doodson, "The Harmonic Development of the Tide-Generating Potential," Proceedings of the Royal Society A (1921)
- Groesbeck, Rowell, Lepofsky & Salomon, "Ancient Clam Gardens Increased Shellfish Production," PLoS ONE (2014)
- Dawson, "Enslaved Ship Pilots in the Age of Revolutions," Journal of Social History (2013)
- MyCoast.org, coastal citizen-science flood monitoring platform
- IPCC, Special Report on the Ocean and Cryosphere (2019)
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