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How to Read a NOAA Tide Station Page

How to Read a NOAA Tide Station Page

NOAA's tidesandcurrents.noaa.gov has the raw data behind every tide chart on this site. Here's how to navigate it for OBX stations.

Every tide chart on this site pulls predictions from NOAA's public tide and current data — specifically the four primary OBX gauges at Duck (8651370), Oregon Inlet (8652587), Hatteras (8654467), and Ocracoke (8654792). If you want to verify a prediction, check live observed water levels, or pull historical data for a past storm, you go directly to NOAA's site. Here's how to navigate it.

The station home page

Each NOAA station has a home page at tidesandcurrents.noaa.gov/stationhome.html?id=XXXXXXX where XXXXXXX is the 7-digit station ID. For Duck, you'd hit ?id=8651370. The home page shows:

  • Current observed water level (live, updated every 6 minutes)
  • Today's predicted tides (high/low times and heights)
  • Last 24 hours of observation on a chart
  • Links to tabular data, datums, harmonic constituents, and meteorological data

Predicted vs observed water level chart

The main chart on each station page shows two curves: a solid blue line for observed water level (what NOAA's sensor is actually measuring right now) and a dashed line for predicted water level (the astronomical-only forecast). The gap between the two is the tide anomaly — usually driven by wind and pressure.

If the observed curve sits consistently above the prediction, expect higher-than-normal high tides and shallower lows. If below, expect lower tides than predicted.

Tabular tide predictions

From the station home page, click Tide Predictions in the left menu. You'll get a multi-day table of high and low tides with times and heights. You can adjust:

  • Date range — up to two years out
  • Datum — usually MLLW (the default for predictions). See our tide datums explainer.
  • Time zone — LST/LDT (local) or GMT
  • Output format — HTML table, CSV, XML, JSON, plain text

The CSV output is perfect for spreadsheet planning of a multi-day trip. Download two weeks of predictions and you can plan every fishing dawn, beach drive, and inlet crossing.

Datums page — what the numbers mean

Click Datums in the left menu. This page lists every reference elevation for the station: MLLW, MLW, MTL, MSL, MHW, MHHW, plus the local conversion to NAVD88 and several historical datums. For most users the key numbers are:

  • MHHW relative to MLLW — tells you the elevation difference between a typical high tide and chart zero. At Duck this is roughly 3.3 ft.
  • Highest observed water level — the record peak at this gauge, with the date. At Duck the record is 5.99 ft above MLLW set during Hurricane Isabel (Sep 2003).
  • Lowest observed water level — record low. Useful for sanity-checking how negative tides can get during big offshore wind events.

Meteorological data

Most primary OBX stations include weather sensors. From the station page, click Meteorological Observations for:

  • Wind speed, direction, gusts (every 6 minutes)
  • Air temperature
  • Water temperature
  • Barometric pressure

The wind data is especially useful for predicting tide anomalies. A 24-hour history of NE winds at 20+ knots tells you to expect a positive anomaly even before a storm starts.

Harmonic constituents — for the curious

If you click Harmonic Constituents, NOAA shows the 37 sinusoidal components that combine to produce the astronomical tide prediction. The dominant ones for OBX stations are M2 (principal lunar semi-diurnal, 12.42 hr period), S2 (principal solar semi-diurnal, 12.00 hr), N2 (larger lunar elliptic, 12.66 hr), K1, and O1 (the declinational tides, 23.9 and 25.8 hr). The amplitude of M2 is by far the largest — that's why the OBX has semi-diurnal tides. See our tide cycle page.

API access for developers

NOAA exposes all of this data through a public REST API at api.tidesandcurrents.noaa.gov/api/prod/datagetter. You can request predictions, observations, harmonic constituents, or meteorological data in JSON, XML, or CSV. The base URL with parameters looks like:

https://api.tidesandcurrents.noaa.gov/api/prod/datagetter
  ?product=predictions
  &station=8651370
  &date=today
  &datum=MLLW
  &time_zone=lst_ldt
  &units=english
  &format=json

This is the same endpoint used to power the interactive charts on this site (via a server-side proxy to handle CORS).

OBX primary stations on NOAA

  • Duck, NC — Station 8651370
  • Oregon Inlet Marina, NC — Station 8652587
  • USCG Station Hatteras Inlet, NC — Station 8654467
  • Ocracoke Inlet (Silver Lake), NC — Station 8654792

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