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FAQ - Tidal Current Predictions and Data

  1. What tidal current predictions and observed current data are available?
  2. What is the relationship between "Tides" and "Tidal Currents"?
  3. How can I get predictions of tidal currents?
  4. What formats are tidal current predictions available in?
  5. Where can I get information about the Gulf Stream?
  6. Where can I get information about currents in the ocean?
  7. How can I get a copy of the program that you use to make tidal current predictions?
  8. I want to develop my own program to predict tidal currents. What information can you provide to help me do this?
  9. Where are the fastest tidal currents?
Q: What tidal current predictions and observed current data are available?

The availability of tidal current predictions and observed current data is limited compared to the availability of tide data. Continuous measurements of currents were not possible until recently. Short deployments of current meters at various estuaries have been carried out for over 100 years. Archived data sets are available but data quality can vary considerably based on the age of the data and location of the measurements. Data from the last 30 years is in digital form; older data exist as paper transcripts. Inquiries about specific locations to ascertain if data exists, its quality and availability will be answered by our office. You can contact our office at (301) 713-2815 between 7AM-3PM Eastern Time. You may also submit an inquiry to our e-mail address at: Tide.Predictions@noaa.gov.

Recent current observations exist where a National Ocean Service (NOS) PORTS is installed, for example, Houston/Galveston, Tampa Bay, San Francisco Bay, New York/New Jersey Harbor, and Narragansett Bay. Historical PORTS data prior to 1999 are available by special request as described above.

NOS tidal current predictions are available in various bays, harbors, estuaries, and within rivers and channels. Inquiries and requests for tidal current predictions should be sent to our office as described above.

Currents are spatially variable, thus predictions should NOT be extrapolated even to nearby locations. Interpolation between two nearby locations should not be attempted. Use of such extrapolations can be hazardous.

Q: What is the relationship between "Tides" and "Tidal Currents"?
Comparison of tidal conditions vs. tidal current phases

The vertical rise and fall of the tides, created by the gravitational force of the Moon and Sun acting on the oceans water, also creates a horizontal motion of the water in the bays, harbors and estuaries. These are tidal currents. In general, as the tides rise there will be a current flowing from the oceans into the bays, harbors and estuaries; this is termed a "flood current". As the tides fall there will be a current flowing towards the oceans; this is termed an "ebb current". There are also periods when there is little or no horizontal motion of the water; this is called "slack water".

Many professional and recreational users of tide and tidal current information have a "rule of thumb" to assume a relationship between the times of high/low tides and the times of the currents. That the times of slack water will be at the same time as the high and low tides, and that the flood and ebb current will occur between the high and low tides. Unfortunately, this assumed "rule of thumb" does not hold for most locations.

The relationship between the times of high/low tide and the times of slack water or maximum current is not a simple one. There are three "base case" conditions. The first is a "standing wave" type of current. In a standing wave the times of slack water will be nearly the same time as the high and low tides, with the maximum flood and ebb current occurring mid way between the high and low tides. The second is a "progressive wave" current. In a progressive wave, the maximum flood and ebb will occur around the times of the high and low tides, with the slack water occurring between the times of high and low tide. The third case is a "hydraulic current". In a hydraulic current, the current is created by the difference in height of the tides at two locations joined by a waterway. The current will be at its maximum flood or ebb when the difference in the two heights are the greatest. The slack water will occur when the height of the tide at the two locations in nearly the same.

Hydraulic currents occur at a limited number of locations. Some examples would be:

  • the Chesapeake and Delaware Canal, which connects the Chesapeake Bay and Delaware Bay
  • the East River in New York, which connects Long Island Sound to New York Harbor
  • certain sections of the Intra Coastal Water Way (ICWW)
  • between barrier islands which create different tidal conditions on opposite sides of the island

Progressive currents are most common at the oceanic entrance to many bays and harbor. Standing wave conditions are most common at the head (most inland point) of larger bays and harbors. Most areas of the coast will fall somewhere in between a progressive and standing wave current. [Example (jpg)] The exact relationship between the times of high and low tides and the maximum current or slack water is unique to each location and cannot be determined from a generic "rule of thumb".

Because the tidal currents are created by the same forces which cause the tides, the currents can be predicted in much the same way as the tides. Observational data on the currents at a location can be analyzed using the same methods employed to analyze tides, and the results of that analysis can be used to generate predictions of tidal currents. However, because the relationship between tides and tidal currents is unique to each location, tide predictions and tidal current predictions are generated separately.

  • Tide predictions provide the times and heights of the tides.
  • Tidal current predictions provide the times and speed of maximum current and times of slack water.

It is up to the user to insure that they are using the correct type of predictions for their activities.

Q: How can I get predictions of tidal currents?

Daily tidal current predictions for the present calendar year are available for more than 2,700 locations along the U.S. coastline from the Max/Min Current Predictions section of our website. The predictions in this section of our wesbite are updated in late October or November to include the next calendar year. For example, the predictions for 2009 will be added to the website in October or November 2008. There are portions of the year when we have both the "old" (2008) and "new year" (2009) predictions; each year of predictions will have a different URL address. If a bookmark or website link is used to access predictions for a specific location, that bookmark/link will need to be updated to access the next year of predictions once they are available.

Daily tidal current predictions of more than one month in length (other than the annual predictions described above) are not available through the web or via e-mail response from our office. You can obtain long-term tide predictions on a calendar-year basis by calling our office at (301) 713-2815 between 7AM-3PM Eastern Time. You may also obtain tide predictions by submitting a request to our e-mail address at: Tide.Predictions@noaa.gov. If you elect to submit your request via e-mail, include the following information:

Your Full Name
Your Full Mailing Address (NOT E-mail)
Your Phone Number (Including Area Code)
The Location(s) for which you want predictions
The Format and Options you want included (see next question below)
- With or Without Daylight Savings Time
- Standard, International, or Manuscript Format

Since Standard and Manuscript formats can be provided in hard copy (paper), diskette or CD; when requesting either of these formats please indicate which media you want provided. If no preference is listed, a paper copy will be provided.

The tidal current predictions will be sent to the mailing address you provide.

PLEASE NOTE
There is a fee for long-term tidal current predictions. Please contact Tide.Predictions@noaa.gov for specific pricing. We are only able to make tidal current predictions for locations where NOS tidal current data has been collected. Please refer to the Tidal Current Predictions section of our website for a list of the available stations.
Q: What formats are tidal current predictions available in?

Tidal current predictions are available in several formats.

International Format - This format is an electronic ASCII file that provides time and speed of current for a single location in a column-delimited format. This format is most suitable for importing into a database, plotting, or other computer program. The following example for ADMIRALTY INLET, WA, 2005 shows the predictions in Pacific Standard Time using 24-hour notation. Tidal current predictions are only available using 24-hour notation for times, but the information can be adjusted to show Daylight Savings Time.

View Sample (Get PDF reader)

Standard Format - This format is available in hard copy and as an electronic ASCII file that provides time and speed of current for a single location in a page-readable format. The following example for ADMIRALTY INLET, WA, 2005 shows the predictions in Pacific Standard Time using 24-hour notation. Tidal current predictions are only available using 24-hour notation for times, but the information can be adjusted to reflect Daylight Savings Time.

View Sample (Get PDF reader)

Manuscript Format - This format is available in hard copy and as an electronic PostScript file that provides time and speed of current for a single location in a 3-month per-page format. This format includes additional information such as the day of week and phases of the moon. The following example for ADMIRALTY INLET, WA, 2005 shows the predictions in 24-Hour Clock (Military Time) and Local Standard Time. Tidal current predictions are only available using 24-hour notation for times, but can be adjusted to reflect Daylight Savings Time.

View Sample (Get PDF reader)

Q: Where can I get information on the Gulf Stream?

The Gulf Stream is an ocean current in the western North Atlantic Ocean that is a major component of the circulation of the water in this ocean basin. It flows generally northward along the U.S. East Coast from Florida to North Carolina. The current turns toward the northeast, away from the U.S. coast in the area of Cape Hatteras, NC.

Knowledge of the position of the Gulf Stream is important to fishermen, weather forecasters, U.S. Coast Guard search-and-rescue operations, and many others. Changes in the position and speed of the Gulf Stream are caused by environmental rather than astronomical effects. NOS does not have observations or predictions available for the Gulf Stream. Gulf Stream analysis and position information is available from a variety of private vendors and other websites, among them:

Q: Where can I get information on currents in the open oceans?

Our office is responsible for information on Tidal Currents. Tidal Currents are the currents caused by the rise and fall of the tides into and out of bays, estuaries, and harbors. We do not have information on currents in the open ocean. One of the following websites may have the information you seek:

Q: How can I get a copy of the program that you use to make tidal current predictions?

Our office offers copies of the program that we use to make predictions for the NOS Tidal Current Reference Stations. Our office is not in the business of software development and distribution. The program we use was developed for our use and is not user-friendly. The program is written in FORTRAN and requires the use of a separate control file for each location that predictions are being made for. This control file must be altered each time you want to make tidal current predictions for different time periods. A copy of the tidal current prediction program is available from our office by calling (301) 713-2815 between 7AM-3PM Eastern Time. You can also submit a request for a copy of the program via e-mail: Tide.Predictions@noaa.gov. If you elect to submit your request via e-mail, include the following information:

Your Full Name
Your Full Mailing Address (NOT E-mail)
Your Phone Number (Including Area Code)
Note in your message that you want the tidal current prediction program
The Location(s) you want control files for.
PLEASE NOTE
There is a fee for a copy of this program. Please contact Tide.Predictions@noaa.gov for specific pricing. The program comes with the control file for one NOS Tidal Current Reference Station of your choice. Additional stations are available.
Q: I want to develop my own program to predict tidal currents. What information can you provide to help me do this?

We can offer you a number of products/services:

  1. Our Restless Tides - This booklet describes the astronomical forces that cause the tides in terms that can be understood by a layperson.
  2. Manual of Harmonic Analysis and Prediction of Tides (Special Pub 98) - This book describes the process of tidal analysis and the mathematics behind tidal predictions. The material covered in the book is fairly detailed, with illustrations, graphs, and tables to provide additional information.
  3. Computer Applications to Tides in the National Ocean Service (Supplement to Special Pub 98) - This booklet describes the methods that NOS uses to predict tides. The booklet contains sample algorithms for tidal data analysis and tidal predictions.
  4. Tidal Current Prediction Package - The predictions package includes a copy of items 2 and 3 listed above. The package also includes a limited copy of the tidal current prediction program (NCP2) used by NOS to generate tidal current predictions. The program is a FORTRAN program and is not very user-friendly. The program requires the use of a control file containing the harmonic constants for each location that tidal currents are to be generated for. This control file has to be altered each time that tidal currents are being predicted for a different time period. Copies of the compiled and source code for the program are provided. The program only works for locations for which harmonic constants are available. These are the NOS tidal current reference stations. The package comes with a control file (harmonic constants) for one Tidal Current Reference Station of your choice. Include your choice of station with your request.
  5. Tidal Current Harmonic Constants - Copies of the tidal current harmonic constants, provided in hard copy or in NCP2 control file format, are available for 50 Tidal Current Reference Stations. These values are provided in the format required by the NCP2 program listed above.
  6. Tidal Current Table 2 Files - These tables list NOS secondary stations. Their tidal current predictions at these stations are generated by applying time and speed corrections to each of the four tidal current phases. There are two Table 2 files for the USA:
    • Tidal Current tables for the Atlantic Coast
    • Tidal Current tables for the Pacific Coast
PLEASE NOTE
There is a fee for each of those products/services. Please contact Tide.Predictions@noaa.gov for specific pricing. As bays and estuaries change due to natural and artificial processes (shoaling, erosion, dredging, construction), the tidal currents in the area can be affected. The tide and tidal current harmonic constants and Table 2 corrections are subject to change as more recent data are received and analyzed.

You can discuss your request or obtain any of the products listed above by calling our office at (301) 713-2815 between 7AM-3PM Eastern Time. You may also request these products by submitting a request to our e-mail address at Tide.Predictions@noaa.gov

If you elect to submit your request via e-mail, include the following information:

Your Full Name
Your Full Mailing Address (NOT E-mail)
Your Phone Number (Including Area Code)
The Information you want

The information requested will be sent to the mailing address you provide along with an invoice for payment.

Q: Where are the fastest tidal currents?

Below is a list of the 50 locations in North America with the fastest tidal currents.

Station Name Latitude Longitude Speed (knots)
Flood Ebb
Seymour Narrows 50 8.00N 125 21.00W 9.2 9.8
Hole In The Wall, Okisollo Channel 50 18.00N 125 13.00W 7.5 7.5
Arran Rapids, north of Stuart Island 50 25.00N 125 8.00W 7.0 7.0
Surge Narrows, Okisollo Channel 50 14.00N 125 10.00W 7.0 7.0
Deception Pass, (Narrows) 48 24.37N 122 38.58W 5.2 6.6
Rapids, near Barnes Bay, Okisollo Channel 50 19.00N 125 16.00W 6.5 6.5
Race Point 50 7.00N 125 20.00W 6.5 6.5
Seechelt Rapids 49 45.00N 123 55.00W 6.5 6.5
Turn Point, Kootznahoo Inlet 57 30.00N 134 35.00W 6.9 6.1
Whirlpool Rapids, Wellbore Channel 50 27.00N 125 47.00W 6.0 6.0
South Inian Pass 58 13.00N 136 21.00W 3.5 6.0
Root Point, Chatham Channel 50 35.00N 126 12.00W 5.5 5.5
Akutan Pass 54 1.00N 166 3.00W 5.8 5.3
Unalga Pass 53 57.00N 166 12.00W 6.3 5.3
Derbin Strait 54 6.00N 165 14.00W 5.8 5.3
Pablo Creek bascule bridge 30 19.40N 81 26.30W 3.4 5.2
Dodd Narrows 49 8.00N 123 49.00W 4.8 5.2
Whale Passage, off Bird Point 57 55.00N 152 48.00W 4.4 5.2
Race Passage 50 23.00N 125 53.00W 4.8 5.2
Current Passage 50 25.00N 125 54.00W 4.8 5.2
Beardslee Island, West of, Glacier Bay 58 28.00N 136 2.00W 5.3 5.1
North Inian Pass 58 17.00N 136 23.00W 2.9 5.1
Shell Point, Blind Channel 50 26.00N 125 31.00W 5.0 5.0
Green Point Rapids, Cordero Channel 50 27.00N 125 31.00W 5.0 5.0
Orange Point 50 4.00N 125 17.00W 5.0 5.0
Yuculta Rapids, SW of Stuart Island 50 21.00N 125 9.00W 5.0 5.0
Off Cape Mudge 50 0.00N 125 14.00W 5.0 5.0
Sergius Narrows 57 24.42N 135 37.87W 6.3 4.9
Baby Pass 53 59.00N 166 4.00W 4.2 4.8
Tuck Narrows, Prince Rupert Harbor 54 24.00N 130 15.00W 5.2 4.8
Little Gull Island, 1.1 miles ENE of 41 13.10N 72 5.10W 4.0 4.7
west of, off 75th Street 40 46.00N 73 57.00W 3.8 4.7
Porlier Pass 49 0.65N 123 35.50W 4.3 4.7
Hell Gate (off Mill Rock) 40 46.70N 73 56.30W 3.4 4.6
Cape Cod Canal, railroad bridge 41 44.50N 70 36.80W 4.0 4.5
Masset Harbor, 5 miles Inside 54 1.00N 132 10.00W 4.0 4.5
Nobles Island, north of 43 6.00N 70 46.00W 3.6 4.4
West Foreland, 1 nmi. east of 60 44.35N 151 38.50W 3.6 4.4
Cairn Point, northwest of (east side) 61 16.03N 149 54.05W 3.2 4.4
Sand Island Tower, southeast of 46 15.17N 123 59.45W 3.0 4.4
Spike Rock 56 36.06N 132 58.56W 4.7 4.3
South Ledge 56 37.00N 132 58.00W 4.7 4.3
Middle Ground Shoal, southeast of 60 50.75N 151 20.20W 3.4 4.3
McGowan, SSW of 46 14.37N 123 54.92W 1.7 4.3
Tlevak Narrows, Turn Point, east of 55 15.87N 133 7.33W 3.0 4.3
Jones Point, Bagaduce River 44 25.55N 68 45.50W 4.2 4.2
West Foreland, 4 nmi. east of 60 43.25N 151 33.60W 4.1 4.1
Lituya Bay entrance 58 37.00N 137 40.00W 5.1 4.1
South Passage 58 14.00N 136 6.00W 2.3 4.1
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Revised: 10/15/2013
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