Field notes
Guides
Short explainers on what the water is doing and why — the theory behind every chart on Perigee's station pages.
How tide predictions work
Why NOAA can publish tide tables years ahead: harmonic constituents, tidal datums, and the difference between a prediction and what the water actually does.
How to read a tide chart
What the curve, the zero line, and a negative tide mean — and how to use high and low tide times to plan fishing, paddling, clamming, or a walk on the flats.
Spring tides, neap tides, and king tides
How the moon's phase and its distance from Earth set the size of the tide — and why the biggest tides of the year arrive when a full or new moon meets perigee.
Minus tides: the best days for tidepooling and clamming
What a minus tide is, why it exposes shore you never normally see, when the biggest ones cluster during the year, and how to plan a safe trip to the flats around one.
Why the tide is different every day
Why high tide arrives about 50 minutes later each day, why the two daily highs rarely match, and why some coasts get one tide a day while others get two.
Tidal datums: what tide heights actually measure
What MLLW, MHW, and mean sea level mean, why a tide height of 0.0 ft doesn't mean no water, and how to read datums when judging depth, clearance, or flood risk.