The highest and lowest water level in each tidal cycle. Most U.S. East Coast stations have two of each per day (about 12 h 25 min apart); much of the Gulf of Mexico has one; the West Coast has two of unequal height.
Slack water
The short period when a tidal current is turning between flood (incoming) and ebb (outgoing) and is near zero. In bays and inlets slack can come well before or after the high or low tide, which is why we show current-station slack times where NOAA publishes them.
Stand of the tide
The period around high or low tide when the water level barely changes. On the open coast it roughly coincides with slack water.
Flood and ebb
The incoming (flood) and outgoing (ebb) tidal current.
Spring tides
Larger-than-average tidal ranges around each new and full moon, when the sun’s and moon’s pull line up. Nothing to do with the season.
Neap tides
Smaller ranges around the first and last quarter moons.
King tide
An informal name for the highest predicted tides of the year, usually when a spring tide coincides with the moon’s perigee. See upcoming king tides.
Minus tide
A low tide that falls below 0 ft on the chart datum (MLLW). Good for clamming, tide-pooling and scouting structure.
MLLW (mean lower low water)
The average of the lower of each day’s two low tides over a 19-year tidal epoch. U.S. charts and predictions use it as 0 ft, so a tide of −1.2 ft is 1.2 ft below that average.
MHHW (mean higher high water)
The average of the higher of each day’s high tides. Tides well above MHHW are where nuisance flooding starts in many places.
Tidal range
The height difference between consecutive high and low tides. Bigger ranges mean stronger currents.
Reference and subordinate stations
NOAA computes predictions for reference stations from harmonic constants derived from long gauge records. Subordinate stations apply time and height offsets to a nearby reference station, so they are slightly less precise.
Tidal epoch
The 19-year period over which datums are averaged (currently 1983–2001 at most stations).