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Great Lakes
Water Level

Meteorological Observations


Bench Mark Data Sheets

Harmonic Constituents

Operational Forecast Systems

PORTS - real-time

Sea Level Trends

Extreme Water Levels

Inundation Analysis



Harmful Algal Blooms

Google Earth/KML Files


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. Links are on the left side of the page. For more information, see the contact information at the bottom of the page.

tide gageTides - 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.

Great Lakes Water Level - The height of the level of water relative to a datum (see below). The Great Lakes are not as affected by gravitational interactions among the sun, moon, and earth as many other areas of the country are, so we cannot measure a predictable tide in these locations. Changes in water level are usually due to weather events. Users can retrieve data from active or historic stations.

current meterCurrents - 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.

Predictions - A calculation of what the water level or current direction 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.

Meteorological Observations - Many water level stations are equipped with meteorological sensors to collect meteorological observations in conjuction 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 conductivity/salinity.

Conductivity - Conductivity is provided at several stations.

bench markBench 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.

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.

full moonHarmonic 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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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