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Tides & Currents Products


NOAA's Tides and Currents website, developed and supported by the Center for Operational Oceanographic Products and Services (CO-OPS), provides the following products. A definition of each term and a description of each product are provided.

Tides / Water Levels


The periodic rise and fall of a body of water resulting from gravitational interactions among the sun, moon, and earth. The vertical component of the particulate motion of a tidal wave. Users can retrieve data from active or historic stations.

Water Levels
The height of the level of water relative to a Datum. Most stations with water level sensors provide readings every six minutes. Some, such as the 1-minute water level stations, provide readings once a minute. CO-OPS measures water levels at coastal stations and at many stations located around the Great Lakes. For coastal stations, water levels have a periodic rise and fall resulting from gravitational interactions among the sun, moon, and earth. For Great Lakes stations, changes in water level are usually due to weather events.

1-minute Water Level Data
CO-OPS provides real-time access to 1-minute water level data to support tsunami detection, warning, and modeling, and support warning and mitigation of other coastal hazards. Data can be viewed numerically or graphically.

NOAA Tide Predictions
A calculation of what the water level will be based on harmonic constituents (see below). This site offers six-minute and hourly tide/water level predictions "on-the-fly" for all stations with harmonic constituents. It also offers high/low data for all stations in NOAA's published tide and current table.

Harmonic Constituents
One of the harmonic elements in a mathematical expression for the tide-producing force and in corresponding formulas for the tide or tidal current. Each constituent represents a periodic change or variation in the relative positions of the earth, moon, and sun. A single constituent is usually written in the form y = A cos (at + "), in which y is a function of time as expressed by the symbol t and is reckoned from a specific origin. The coefficient A is called the amplitude of the constituent and is a measure of its relative importance. The angle (at + ") changes uniformly and its value at any time is called the phase of the constituent. The speed of the constituent is the rate of change in its phase and is represented by the symbol "a" in the formula. The quantity is the phase of the constituent at the initial instant from which the time is reckoned. The period of the constituent is the time required for the phase to change through 360° and is the cycle of the astronomical condition represented by the constituent.

Datums
For marine applications, a base elevation used as a reference from which to reckon heights or depths. It is called a tidal datum when defined in terms of a certain phase of the tide. Tidal datums are local datums and should not be extended into areas that have differing hydrographic characteristics without substantiating measurements. In order that they may be recovered when needed, such datums are referenced to fixed points known as benchmarks. The "Present Epoch" is from 1983-2001 and includes the latest datums available. The "Superseded Epoch" is from 1960-1978 and has been replaced by the "Present" datums, or was not replaced due to insufficient data.

Bench Mark Data Sheets
A fixed physical object or mark used as reference for a horizontal or vertical datum. A tidal bench mark is one near a tide station to which the tide staff and tidal datums are referred. A primary bench mark is the principal mark of a group of tidal bench marks to which the tide staff and tidal datums are referred. The standard tidal bench mark of the National Ocean Service is a brass, bronze, or aluminum alloy disk 3 1/2 inches in diameter containing the inscription NATIONAL OCEAN SERVICE together with other individual identifying information. The "Present Epoch" is from 1983-2001 and is the latest bench mark sheet available. The "Superseded Epoch" is from 1960-1978 and has been replaced by a "Present" sheet or was not replaced due to insufficient data.

Sea Level Trends
The rate of mean sea level rise or fall has been determined for 117 long-term water level stations. Monthly mean sea level data were used to obtain the linear trend, the average seasonal cycle, and the interannual variations. The linear trend at a coastal location is primarily a combination of the global sea-level rise and any local vertical land movement. The seasonal cycle and interannual variations are caused by fluctuations in coastal ocean temperatures, salinities, winds, atmospheric pressures, and currents. The interannual variations for many Pacific stations are closely related to the El Nino/Southern Oscillation. Assuming no change in trend, the time series of interannual variations are extended up to the latest month, and maps are created to show the regional extent of anomalously high or low water levels.

Sea Level Trends are available for both coastal and global stations.

Extreme Water Levels
Exceedance Probability Statistics on Extreme Water Levels now available for select water level stations in California, Oregon, Washington, and the Pacific Islands.

Reports
Various water level reports in table and report format.

Inundation Analysis
Frequency and duration of inundation statistics above a specified elevation threshold are now available using observed and historical data from NOAA Center for Operational Oceanographic Products and Services' tide stations.

Publications

CO-OPS Publications
The publications section is an extensive collection of CO-OPS recent and historic publications, including informational pamphlets, technical reports, technical memorandums, manuals and standards publications, storm reports, historical data reports and other popular publications. Most of the publications are available via PDF, others are described by an abstract and information on how to obtain them.

CO-OPS Field Library
The CO-OPS Field Library is a public document repository for manuals, standard operating procedures, publications and other documents and is maintained by the Center for Operational Oceanographic Products and Services (CO-OPS). Documents may be searched using title, author, and keyword/tags and can be downloaded using the filename link.

Historic Tide and Tidal Current Tables
NOAA's National Ocean Services (NOS) and predecessor offices have been annually publishing tide and tidal current predictions in hard-copy format, entitled "Tide Tables" and "Tidal Current Tables", since the 1860's. Electronic copies of the published "Tide Tables" and "Tidal Current Tables" from past year, as PDF documents, are made available through this page of the Tides & Currents website. Additional historic publications of the "Tide Tables" and "Tidal Current Tables" will be made available when they are converted to an electronic format.

Currents

Currents
Generally, a horizontal movement of water. Currents may be classified as tidal and nontidal. Tidal currents are caused by gravitational interactions among the sun, moon, and earth and are part of the same general movement of the sea that is manifested in the vertical rise and fall, called tide. Tidal currents are periodic, with a net velocity of zero over the particular tidal cycle. See tidalwave. Nontidal currents include the permanent currents in the general circulatory systems of the sea, as well as temporary currents arising from more pronounced meteorological variability.

Historic Current Data

Each year, CO-OPS measures currents at many coastal locations in order to provide accurate tidal current predictions for the maritime community. These data sets typically range from one to three months in length and at most locations, data are available throughout the water column. This page contains the raw current measurements taken during these surveys, which date back to 1997.

Tidal Current Predictions
A calculation of what the current direction and speed will be based on harmonic constituents (see above). CO-OPS offers predicted time and speed of maximum flood/ebb and timing of slack water (no current) for all stations in NOAA's published current tables.

NOAA Current Predictions Beta
This new site offers expanded tidal current predictions for stations in NOAA's published tide and current tables. Customized predictions are calculated "on-the-fly" and are available in graphical and text format. Six-minute, half-hour and hourly tidal current predictions can be generated for all stations with harmonic constituents. The product also offers predicted time and speed of maximum flood/ebb and timing of slack water (no current) for all stations in NOAA's published current tables. Predictions can be downloaded in text, CSV, XML and PDF formats.

HF Radar Surface Currents
This product provides near real-time surface current observations and tidal current predictions from High Frequency Radar in estuarine and coastal locations. Hourly surface currents are presented via an interactive map and time series plots for 48 hours before and 48 hours after the present time.

Meteorological

Meteorological Observations
Many stations are equipped with meteorological sensors to collect meteorological observations in conjunction with water level data. The following observations may be retrieved from this website: wind speed and directions, air temperature, water temperature, barometric pressure, relative humidity, and visibility. Not every station has the full suite of sensors installed.

Water Temp/Conductivity
Water temperature and/or conductivity observations.

Astronomical
Of all the constituents, the moon has the greatest effect on tides. This page provides information on the various phases of the moon.

Physical Oceanographic Real-Time System (PORTS®)

PORTS®
PORTS® is a decision support tool that improves the safety and efficiency of maritime commerce and coastal resource management through the integration of real-time environmental observations and predictions.

MyPORTS®
MyPORTS is an application designed to let you create your own customized PORTS® pages.

Modeling

Operational Forecast Systems
Nowcasts and forecast guidance are scientific predictions about the present and future states, respectively, of water levels (and possibly currents and other relevant oceanographic variables, such as salinity and temperature) in a coastal area made by a numerical model. These predictions rely on either observed or forecast data. A nowcast incorporates recent (and often near real-time) observed meteorological, oceanographic, and/or river flow rate data. A nowcast covers the period of time from the recent past (e.g., the past few days) to the present, and it makes predictions for locations where observational data are not available. The present is the time at which the nowcast is made, and at which the most recent observations are from a few minutes to an hour old. A forecast guidance incorporates meteorological, oceanographic, and/or river flow rate forecasts and makes predictions for locations where observational data will not be available. A forecast guidance is usually initialized by the results of a nowcast.

Harmful Algal Blooms
The Harmful Algal Bloom Forecast System (HAB-FS) provides advance notice of harmful algal blooms, including possible impacts to the public, location, extent, and the potential for HAB development or movement.

Links / Web Services

Tides Online
Tides Online was developed to show a list of water level stations that are being affected by a storm. It has since become a quick and easy way to view data for any station of interest.

Great Lakes Online
A sister page to Tides Online focused specifically on the Great Lakes region.

IOOS Data Portal
This is your gateway to the Center for Operational Oceanographic Products and Services (CO-OPS) one stop for data access using NOAA's Integrated Ocean Observing System (IOOS) Sensor Observational Service, Web Services, OPeNDAP, NetCDF model data, stations information and other services.

nowCOAST
NowCOAST is a web mapping portal providing spatially referenced links to thousands of real-time coastal observations and NOAA forecasts of interest to the marine community.

Storm QuickLooks

The Storm QuickLook product provides a real-time synopsis of oceanographic information when coastal areas are threatened by a tropical storm or hurricane. The product integrates water level and meteorological observations with National Weather Service tropical cyclone track and intensity information.

Google Earth/KML Files
CO-OPS offers certain data sets as Google Earth KML/KMZ files for download. KML/KMZ files allow users to view CO-OPS' data within the Google Earth application.

Tides & Currents Station Map
The station map is a convenient zoomable interface that allows the user to quickly identify an area of interest, such as a state, and see all active observing stations in that area with a listing of the types of data available at each site. Hovering the mouse over the site icon reveals the latest data listing, and clicking on the icon will bring up the data graphs below the map. Search criteria along the right margin allow the user to identify various data products, geographic regions, or data types from both active and historical sites.

CO-OPS Data API
The CO-OPS Data API is a flexible retrieval mechanism for direct access to CO-OPS' products, such as water levels, predictions, currents, meteorological observations, and more. Users can retrieve output in multiple common formats.

Revised: 10/15/2013
NOAA / National Ocean Service
Web site owner: Center for Operational Oceanographic Products and Services