Which tide stations does Tidesy use, and why?
Every Tidesy gets its tides from NOAA, the same source that charts, harbor masters and the Coast Guard rely on. But NOAA publishes predictions for about 3,500 places, and they aren't all made the same way. Here's which ones Tidesy uses, why we chose them, and how you can see exactly where your tides come from.
Tidesy uses NOAA's harmonic stations
A harmonic station is a place where NOAA measured the water level for a long time, often many years, and broke the tide down into its individual rhythms: the pull of the moon and the sun, the shape of the coastline and the sea floor, and dozens of smaller effects. Those rhythms, called harmonic constituents, give the station its own tide model. With it, NOAA can calculate the water level at that exact spot for any moment, past or future.
NOAA has about 1,260 harmonic stations around the country, and Tidesy can use any of them.
Why harmonic stations
The whole tide, not just the highs and lows
For a harmonic station, NOAA predicts the water level every six minutes, all day long. That's what lets Tidesy draw a smooth tide curve and show where the water is right now, whether it's rising or falling, and how fast, not just the time of the next high or low.
Live gauges
238 of NOAA's harmonic stations have a working tide gauge that measures the real water level every six minutes. Predictions describe the ocean on an ordinary day; wind, storms, river flow and air pressure can push the water a foot or more away from them. When your station has a gauge and Flood Risk is turned on, Tidesy plots the measured water level right on top of the predicted curve, so you can see at a glance whether the ocean is following the forecast. Stations without a gauge are marked "NO GAUGE," so you always know which kind of information you're looking at.
Data you can trust and check
Each harmonic station's model is built from its own long record of measurements, and the ones with gauges are compared against the real water every day.
NOAA's other kind of station, the subordinate station, works differently. It has no tide model of its own. Its predictions are borrowed from a harmonic "reference station" and adjusted with a few fixed corrections, such as "high tide 40 minutes later and 10% higher." Those corrections usually come from a much shorter set of measurements, sometimes taken decades ago, and no subordinate station has a live gauge to check them against. Many are perfectly good. But if a channel has shifted or a jetty has been built since the corrections were measured, nothing in the data tells you so.
An example: Tillamook Bay, Oregon
NOAA's station for the town of Tillamook, on Hoquarten Slough, is a subordinate station. Its reference station is Crescent City, California, about 257 miles to the south. Its predictions are Crescent City's tides with high tides moved 1 hour 52 minutes later and low tides 3 hours 15 minutes later.
Tillamook Bay also has two harmonic stations of its own: Dick Point, inside the bay about 3 miles from town, and Garibaldi, near the mouth of the bay about 7 miles away, which has a live gauge. Here's Thanksgiving Day 2026 at all four:
| Station | Kind | Afternoon high | Evening low |
|---|---|---|---|
| Crescent City, CA | Harmonic, live gauge | 11:45 AM, 8.5 ft | 7:02 PM, −1.9 ft |
| Tillamook, Hoquarten Slough | Subordinate (from Crescent City) | 1:37 PM, 8.0 ft | 10:17 PM, −1.1 ft |
| Dick Point, Tillamook Bay | Harmonic | 1:37 PM, 8.6 ft | 9:54 PM, −0.7 ft |
| Garibaldi, Tillamook Bay | Harmonic, live gauge | 1:11 PM, 10.1 ft | 8:02 PM, −1.9 ft |
Two things stand out. First, the tide changes a lot within one bay: the evening low reaches Dick Point almost two hours after it reaches Garibaldi, and doesn't drop nearly as far. Second, the Dick Point and Garibaldi numbers each come from measurements taken in Tillamook Bay itself, and Garibaldi's gauge shows the real water level in the bay every six minutes. The slough's numbers are a California tide, shifted.
A Tidesy shipped to Tillamook starts with Garibaldi, so its live gauge shows what the bay is really doing. Want the tide closer to town too? Add Dick Point as one of your stations.
How Tidesy picks your stations
- Set up before it ships. When we build your Tidesy, we preload it with the harmonic stations closest to your shipping address. If it's a gift, just tell us where it's going.
- Up to three at once. Tidesy shows up to three stations, so you can follow the tide where you live, where you fish and where you walk the beach.
- Yours to change. You can switch to any of NOAA's 1,260 harmonic stations at any time from your Tidesy's web page.
All the information, in your hands
We think you should know exactly where your tides come from, so Tidesy never hides it.
- Every station links to its source. On your Tidesy's web page, each station's number links straight to its page on NOAA's website, with its location, history and data.
- You can see the gauge. With Flood Risk on, stations with a live gauge show the measured water level on the tide curve, and stations without one say "NO GAUGE."
- You can compare with the station down the road. Look up any place on NOAA's tide predictions page. If it's a subordinate station, NOAA lists its reference station and corrections, so you can see how its tide relates to the ones on your Tidesy.
Our own Tidesy
Our home is in Ocean Park, Washington, on the Long Beach Peninsula, and our Tidesy uses the Cape Disappointment station at the mouth of the Columbia River, about 14 miles south. It's a harmonic station with a live gauge, and it matches what we see on the beach.
Curious which stations are near you? Get in touch. We're happy to look them up with you.