Guide
Reading a tide table on this coast
Checked September 17, 2026 against NOAA Tides and Currents and the Bureau of Land Management.
The Tides tile repeats NOAA’s predictions for the station nearest the town you are reading for. This page explains what the zero on that scale is, which stations on this coast are measured and which are worked out from somewhere else, and why the water is not always where the prediction says.
Zero is not the sea bed
Every tide height on this coast is measured from mean lower low water — MLLW — which NOAA defines as “the average of the lower low water height of each tidal day observed over the National Tidal Datum Epoch.” In plainer terms: of the two low tides most days bring, take the lower one, and average it over about nineteen years. That average is zero.
Because it is an average, roughly half of all lower low tides fall below it. A prediction of −1.5 ft is not an error; it is a tide a foot and a half lower than the long-run average low — the tide a tidepooler wants and a boat in Humboldt Bay’s shallows does not.
It also means a charted depth of 6 feet is 6 feet at MLLW. On a minus tide there is less water over it than the chart says.
Some stations have constants. Some are offsets.
NOAA separates stations with their own tidal harmonic constants from stations without. A harmonic station’s predictions “are generated directly from the harmonic constants.” A subordinate station has none, so NOAA predicts the highs and lows at a reference station and then applies time and height adjustments.
That is a difference in arithmetic, and it is not the same thing as whether there is an instrument in the water. Of the ten stations on these two boards, only Crescent City has a water level gauge reporting in real time. Humboldt Bay’s gauge is at North Spit, near the entrance, and the board does not show it as a town station; three of the bay’s stations are predicted from it.
| Station | Kind | Worked out from |
|---|---|---|
| Pyramid Point, Smith River 9419945 | Harmonic | — |
| Crescent City 9419750 | Harmonic, live gauge | — |
| Trinidad Harbor 9419059 | Subordinate | Crescent City, 2 to 3 minutes earlier |
| Mad River Slough 9418865 | Subordinate | North Spit, 35 to 43 minutes later |
| Arcata Wharf 9418851 | Subordinate | North Spit, 48 to 54 minutes later |
| Samoa 9418817 | Harmonic | — |
| Eureka 9418801 | Subordinate | North Spit, 13 to 26 minutes later |
| Fields Landing 9418723 | Harmonic | — |
| Eel River, Cockrobin Island bridge 9418637 | Harmonic | — |
| Shelter Cove 9418024 | Harmonic | — |
The lag up the bay is real and worth knowing: the tide at Arcata Wharf turns most of an hour after it does at North Spit. Read the station for where you will be, not the one nearest the entrance.
The Lost Coast Trail runs on the tide table
South of Petrolia, the Bureau of Land Management’s King Range trail follows the beach, and parts of it go under water. BLM: “Be aware of the tide! Carry a tide table and hike these stretches during an outgoing tide of three feet or less to avoid being trapped.” The stretches it names are near Punta Gorda, Sea Lion Gulch to Randall Creek, and Miller Flat to Gitchell Creek.
BLM’s trip planning guide is more exact, and stricter in one place: Punta Gorda passable under about 6 feet, Sea Lion Gulch to Randall Creek under 2.5 feet, entered only on a falling tide, and Miller to Gitchell under 3 feet. The King Range tide flyer names the station to read: Shelter Cove, 9418024 — the one this board shows for Shelter Cove and Petrolia.
Why the water is not where the prediction said
NOAA is direct about the limits of a tide table:
“We can only predict the astronomical tides; water level changes created by the gravity of the Moon, and the relative motions of the Earth, Sun and Moon.”
“We cannot predict the effect that wind, rain, freshwater runoff, and other short-term meteorological events will have on the tides.”
On this coast those are routine. A winter storm’s wind and low pressure hold the sea higher than predicted. Rain down the Eel, the Mad, the Klamath or the Smith raises the level in the lower rivers and sloughs and can hold the ebb back. And a big swell pushes water far higher up a beach than any tide height: the Eureka weather office warns that sneaker waves “can strike without warning”, on any tide. A three-foot tide on the table is not a three-foot beach.
Where a station has a live gauge, the observed level is the answer; where it does not, treat the prediction as the start of the question.
Sources
- NOAA Tides and Currents, tidal datums — the definition of MLLW
- NOAA Tides and Currents, page help — harmonic and subordinate stations in NOAA’s own words
- NOAA Tides and Currents, frequently asked questions — what a prediction can and cannot include
- Bureau of Land Management, Lost Coast Trail and King Range trip planning guide — the impassable zones and their tide heights
- National Weather Service Eureka, beach safety brochure
- Station pages: Pyramid Point, Crescent City, Trinidad Harbor, Mad River Slough, Arcata Wharf, Samoa, Eureka, North Spit, Fields Landing, Eel River, Shelter Cove