Choosing a NOAA tide, water-level or current product

Height and flow are not the same quantity

A tide graph describes changing water height, while a current product describes horizontal movement. NOAA's tides and currents explanation distinguishes these processes and describes the roles of tides, wind and density differences in moving water. This is the first useful check when opening a coastal data page: is its vertical axis a height or a speed? Similar-looking curves do not mean two products are interchangeable. A height reading alone is not a measurement of how fast water is moving beside a vessel.

Select a product that answers your question

NOAA's CO-OPS product directory separates tide predictions, observed and historical water levels, current observations and predictions, and regional forecast systems. For a question about a measured past level, use observations for that station and date. For an expected tidal pattern, use the prediction product and keep that label. A forecast is another product with its own scope. Choosing one deliberately is more informative than searching for an unspecified tide map and assuming its first result is a current observation.

Check the station, datum and clock

The NOAA Tides and Currents FAQ discusses tide and current tables, prediction accuracy and vertical references. A datum is the reference against which a height is stated. Two heights are not directly comparable merely because both are displayed in feet. In a comparison note, retain the station identifier, datum, units and time zone. Do not silently mix local time and UTC. Also distinguish the instant represented by a plotted point from the time you downloaded or refreshed the web page.

Read differences before assigning a cause

If an observed line and a predicted line diverge, first make sure they represent the same station, time and reference settings. Do not turn a visual difference into a precise storm-surge claim without the relevant source explanation. A gap in an observation series is not a zero water level, and an old last reading is not a measurement of the present. If one graph is unavailable, label the comparison incomplete. Interpolating a missing value yourself should never be presented as an official measurement or used to establish safe clearance.

Keep vessel context separate from environmental data

PocketWorld's ship mode lets you inspect available AIS reports and the geography around a coast or harbour. This page does not add a NOAA tide station, current forecast or navigational chart layer to that mode. Use the linked NOAA products for those measurements and preserve their timestamps when comparing them with a vessel report. Our educational map cannot determine a safe transit time, water depth or route. The useful outcome here is knowing which product you are reading and what it can support, not deriving operational advice from a ship icon and a nearby graph.