CoastCue field guide

Reference and subordinate tide stations are not the same thing

NOAA publishes two kinds of tide-prediction stations. Both provide official tide times, but the way those predictions are produced is materially different.

Reference prediction stations

A reference station has harmonic constituents used to calculate its prediction directly. It can support a continuous predicted curve as well as high and low events. Reference describes the prediction method. It does not automatically mean every displayed value is a live measurement.

Subordinate prediction stations

A subordinate station derives its prediction from a named reference station using NOAA-published time and height offsets. This expands useful coverage into creeks, beaches, and inlets without pretending each point has a permanent instrument. CoastCue identifies the reference station whenever NOAA publishes that relationship.

A sensor is a separate question

Station type and live observation capability are independent. A tide-prediction point may have predictions but no current water-level sensor. CoastCue checks NOAA's water-level observation catalog separately and labels the result. A predicted chart never becomes observed merely because it looks precise.

Why some curves are estimated

Subordinate stations may publish official high and low events without a continuous six-minute prediction series. CoastCue can interpolate between those events for a planning curve, but labels that line Estimated. The high and low events remain NOAA predictions; the points drawn between them are CoastCue's transparent interpolation.