CoastCoastCue field guide
What MLLW actually means
MLLW is the reference line behind most United States tide predictions. It is useful precisely because everyone can measure from the same baseline, but it is easy to mistake for the shoreline, zero depth, or the current water level.
The lower low averaged over an epoch
Many coastal locations have two low tides each day with different heights. NOAA averages the lower of those daily lows over an official 19-year datum epoch. That statistical surface becomes Mean Lower Low Water. A predicted height of 0.5 feet means the water surface is predicted to be half a foot above MLLW at that station.
Why it is not depth
A tide height is a water-surface elevation relative to a datum. Actual depth also depends on the surveyed bottom elevation, shoaling, dredging, waves, and where you are relative to the station. CoastCue is planning software, not a navigation chart or depth sounder.
Why datums differ
MHW, MHHW, MTL, NAVD88, and MLLW answer different questions. Mixing them can make two correct numbers look contradictory. CoastCue keeps the datum beside the value and does not silently translate between vertical reference systems.
Subordinate stations and MLLW
A subordinate prediction station applies NOAA-published time and height offsets to a reference station. Its predictions can still be published in MLLW, but the location may not have its own live sensor or a full set of station datums. That limitation belongs on the page, not hidden behind a generic chart.