Tide and current data is available from NOAA's Center for Operational Products and Services website

Tides Tide Predictions. Generate a graphical display or a tabular listing of daily high and low tide predictions for more than 3,000 locations around the nation. Predictions may be generated up to two years in advance.

Real-Time Tide Data. Access current water levels from over 3,000 tidal stations. For the Great Lakes region, see Great Lakes Real-Time Water Level Data.

Historic Tide Data. For a given NOAA tide station, retrieve historic tide data from the earliest to the most recent dates for which data is available. For the Great Lakes region, see Great Lakes Historic Water Level Data.

Sea Levels. View a global map depicting regional trends in sea level, with arrows representing the direction and magnitude of change.

Tides Online. Choose a tide station by state and location to view current tidal information, wind speeds, air pressure, and air temperature. For the Great Lakes region, visit Great Lakes Online.

Tsunami-Capable Tide Stations. Access high resolution, one-minute water level sample data used to support national tsunami warning and mitigation efforts.

Tide Station Index. Generate a per-state list of all NOAA tide stations, including station number, name, location, installation date, and more.

Tidal Datums. Access NOAA's tidal datums. Scientists use datums to define "normal" water levels as a starting point from which all measurements are made. The numbers that appear on a nautical chart represent water depths measured relative to such a datum.

Currents Real-Time Current Data. View real-time current data collected by NOAA current meters around the nation.

Historic Current Data. View historic current data collected by active and retired NOAA current meters around the nation.

Tidal Current Predictions. Obtain tidal current predictions for more than 2700 tidal current stations nationwide.

Other CO-OPS Products and Services PORTS®. NOAA's Physical Oceanographic Real-Time System (PORTS®) improves the safety and efficiency of maritime commerce and coastal resource management through the integration of real-time environmental observations, forecasts and other geospatial information. PORTS® measures and disseminates observations and predictions of water levels, currents, salinity, and meteorological parameters (e.g., winds, atmospheric pressure, air and water temperatures) that mariners need to navigate safely in and around key maritime ports around the nation.

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

Storm QuickLook. Access near real-time oceanographic and meteorological observations at locations affected by a tropical cyclone.

Operational Forecast System. This service offers nowcasts and short-term forecasts for select regions (critical ports, harbors, estuaries, Great Lakes, and coastal waters). These real-time observations and forecasts deliver present and future states of water levels, along with currents and other relevant oceanographic variables, such as salinity and temperature.

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Part of each station is a recorder which sends an audio signal down a half-inch-wide sounding tube and measures the time it takes for the reflected signal to travel back from the water's surface.

In addition to measuring tidal heights, these stations also record 11 different oceanographic and meteorological parameters including wind speed and direction, water current speed and direction, air and water temperature, and barometric pressure.

The stations collect data every six minutes with timing controlled by a Geostationary Operational Environmental Satellite (GOES). The stations also use these satellites to transmit their data hourly to NOAA headquarters. In the event of a storm, the stations can be programmed to transmit their data every six minutes. Field teams can quickly check and maintain the systems using laptop computers. In addition, all of the raw and processed data are available over the Internet. For more information:
Center for Operational Oceanographic Products and Services
Measuring Tides (Diving Deeper podcast, 6.16.10)

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Storm surge is the water that is pushed toward the shoreline by the force of winds from a hurricane or other intense storm. When combined with normal tides, the surge can create water levels 15 feet or more about the mean water level. This rise in water can cause severe flooding in coastal areas.

A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon, and Earth. The term “tidal wave” is often used to refer to tsunamis; however, this reference is incorrect as tsunamis have nothing to do with tides.

For more information:
Storm Surge, National Hurricane Center
Center for Operational Oceanographic Products and Services

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Scientists measure the times, heights, and extents of both the inflow and outflow of the tidal waters that support a number of different aspects of our daily lives. Navigating ships safely through shallow water ports, intracoastal waterways, and estuaries requires knowledge of the time and height of the tides as well as the speed and direction of the tidal currents. Mariners need accurate data because the depths and widths of the channels and increased marine traffic leaves very little room for error.

Engineers need data to monitor fluctuating tide levels for harbor engineering projects such as the construction of bridges and docks. Projects involving the construction, demolition, or movement of large structures must be scheduled far in advance if an area experiences wide fluctuations in water levels during its tidal cycle. Habitat restoration projects also require accurate knowledge of tide and current conditions.

Tidal data is also critical to fishing, recreational boating, and surfing. Commercial and recreational fishermen use their knowledge of the tides and tidal currents to help them improve their catches. Depending on the species and water depth in a particular area, fish may concentrate during ebb or flood tidal currents.

For more information:
Center for Operational Oceanographic Products and Services
NOS Education Tutorial: Tides
Diving Deeper Podcast, Episode 6 (Apr. 8, 2009) - What are tides?

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A lunar day is how long it takes for one point on the Earth to make one complete rotation and end up at the same point in relation to the moon. The reason that a lunar day is longer than a normal 24-hour day is because the moon rotates around the Earth in the same direction that the Earth is spinning. It takes the Earth an extra 50 minutes to “catch up” to the moon.

Tides are very long waves that move across the oceans. They are caused by the gravitational forces exerted on the earth by the moon, and to a lesser extent, the sun. When the highest point in the wave, or the crest, reaches a coast, the coast experiences a high tide. When the lowest point, or the trough, reaches a coast, the coast experiences a low tide.

Imagine the ocean is shaped like a football pointing at the moon. The football’s pointed ends represent the parts of the Earth experiencing high tide and the football’s flat sides are the parts of the earth experiencing low tide.

The point facing the moon is formed because the gravitational pull of the moon is strongest on whichever side of the Earth faces it. Gravity pulls the ocean towards the moon and high tide occurs.

The bulge on the far side of the Earth is caused by inertia. The water moving away from the moon resists the gravitational forces that attempt to pull it in the opposite direction. Because the gravitational pull of the moon is weaker on the far side of the Earth, inertia wins, the ocean bulges out and high tide occurs.

As the Earth spins, different areas of the planet face the moon, and this rotation causes the tides to cycle around the planet.

NOS scientists advanced tidal recording systems as well as satellite imagery to monitor tides and water levels. These data are used to predict ocean behavior in order to protect our coasts and coastal communities.

For more information:
Center for Operational Oceanographic Products and Services
Tides Tutorial, NOS Education
What are Tides? - Diving Deeper audio podcast

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The Center for Operational Oceanographic Products and Services (CO-OPS) is primarily responsible for predicting and measuring water levels and currents and disseminating this information. CO-OPS collects, analyzes, and distributes such data to maintain safe maritime navigation and waterborne commerce.

While CO-OPS computes tidal predictions for more than 3,000 water-level stations around the United States, the publication of full daily predictions is limited to fewer stations. Stations with full daily predictions are called “reference stations” and remaining stations are called “subordinate stations.” You can calculate tidal predictions for subordinate stations by applying specific differences to the times and heights of tides of the specified reference stations.

To access tidal predictions for 2009, as well as 2008 – 2004, visit the CO-OPS Water Level Tidal Predictions Web page. For more information:
Water Level Tidal Predictions, Center for Operational Oceanographic Products and Services
Tides and Water Levels, NOS Education
Changing Technology for Real-Time Tide Measurements, NOAA 200th Anniversary Web Site

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The highest tides in the world can be found in Canada at the Bay of Fundy, which separates New Brunswick from Nova Scotia.

At some times of the year the difference between high and low tide in this Bay is 16.3 meters (53.5 feet), taller than a three-story building.

Anchorage, Alaska, comes in at a close second with tidal ranges up to 12.2 meters (40 feet).

At increasing lattitudes (as one moves further from the equator and closer to the poles) there often is a dramatic increase in tidal range.

Tidal highs and lows depend on a lot of different factors. The shape and geometry of a coastline play a major role, as do the locations of the Sun and Moon. Storm systems at sea and on land also shift large quantities of water around and affect the tides. Detailed forecasts are available for high and low tides in all sea ports, but are specific to local conditions.

 

For more information:
Tides and Water Levels, NOS Education
Tides Online, Center for Operational Oceanographic Products and Services

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Tides are one of the most reliable phenomena in the world. As the sun rises in the east and the stars come out at night, we are confident that the ocean waters will regularly rise and fall along our shores.

Tides are very long-period waves that move through the oceans in response to the forces exerted by the moon and sun. Tides originate in the oceans and progress toward the coastlines where they appear as the regular rise and fall of the sea surface.

When the highest part, or crest, of the wave reaches a particular location, high tide occurs; low tide corresponds to the lowest part of the wave, or its trough. The difference in height between the high tide and the low tide is called the tidal range.

For more information:
Tides and Water Levels, NOS Education
Tides Online, Center for Operational Oceanographic Products and Services

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Tides are driven by the gravitational force of the moon and sun. Tides are characterized by water moving up and down over a long period of time.

When used in association with water, the term "current" describes the motion of the water. Oceanic currents are driven by several factors. One is the rise and fall of the tides. Tides create a current in the oceans, near the shore, and in bays and estuaries along the coast. These are called "tidal currents." Tidal currents are the only type of currents that change in a very regular pattern and can be predicted for future dates.

A second factor that drives ocean currents is wind. Winds drive currents that are at or near the ocean's surface. These currents are generally measured in meters per second or in knots (1 knot = 1.85 kilometers per hour or 1.15 miles per hour). Winds drive currents near coastal areas on a localized scale and in the open ocean on a global scale.

A third factor that drives currents is thermohaline circulation - a process driven by density differences in water due to temperature (thermo) and salinity (haline) in different parts of the ocean. Currents driven by thermohaline circulation occur at both deep and shallow ocean levels and move much slower than tidal or surface currents.

For more information:
Currents, NOS Education
Tides and Currents
Major Ocean Currents, JetStream, the National Weather Service Online Weather School
Rip Currents, JetStream, the National Weather Service Online Weather School

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