How we know the tides
The same method NOAA uses, extended one honest step
All times are island time.
Where the numbers come from
There is no tide gauge sitting on Bowman's Beach, or on most of the beaches you walk. What NOAA publishes for this stretch of coast are predictions for a handful of reference and subordinate stations. A subordinate station is one whose tide is figured from a bigger reference gauge by a fixed set of offsets. We use exactly the same public predictions, and the same offset method, and then we go one step further so that every beach gets its own answer instead of borrowing the nearest station's.
Heights are shown against MLLW (mean lower low water, the datum NOAA charts use), which is just the low-water line the numbers are measured from. A minus tide is a low that drops below it, and those are the mornings that open up the most sand.
The NOAA offsets we start from
Each subordinate station's tide is computed from the St. Petersburg reference station: shift each high and low by a set number of minutes, then scale its height. These are the published constants, committed in our data and re-verified against NOAA every quarter.
| Station | High-tide time offset | Low-tide time offset | Height scale |
|---|---|---|---|
| Point Ybel (San Carlos Bay entrance) | -110 min | -72 min | ×1.21 |
| Redfish Pass, Captiva (north end) | -55 min | -74 min | ×0.91 |
| Captiva, Pine Island Sound | -46 min | -20 min | ×0.91 |
A negative offset means that station's tide arrives earlier than the reference; the height scale stretches or shrinks the reference height to match.
How we interpolate a tide for your beach
Along the Gulf shore, each beach sits somewhere between the two nearest stations. We walk the coastline as a hand-digitized path and measure how far along it your beach lies between those two anchors. A beach a quarter of the way along gets a quarter of the second station and three-quarters of the first. For every matched high and low, we blend the two stations' times and heights by that along-shore fraction. This interpolation is what gives a beach in the middle of the island its own tide rather than the nearest gauge's.
The blend only ever happens between two stations inside the same stretch of coast; no estimate is carried across Blind Pass or Redfish Pass, where the tide genuinely changes character. Points right at a pass, or on the bay side, are snapped straight to their nearest harmonic station instead of interpolated. For those, the honest answer is the station's own tide, so that is what we show.
When the water runs off the chart: the anomaly layer
Predictions are astronomy: sun, moon, and the shape of the coast. They cannot know that a week of onshore wind has stacked extra water against the islands, or that a cold front has pushed it back out. So we also read the live gauge up the Caloosahatchee at Fort Myers, compare what the water is actually doing against what the chart predicted for that same moment, and, when the two disagree by a quarter-foot or more on two readings in a row, we say so in plain inches. It is a trend from a gauge miles away, not a beach-exact height, and we label it that way. If the gauge goes quiet, the note simply disappears rather than showing you something stale.
What this is, and what it is not
These are estimates built to help you time a walk on the beach, not to move a boat. Where a beach's tide is blended from two stations we mark it as derived and link back to this page, so nothing on the site claims a precision it does not have.
