Tide Predictions and Data
What other WWW sites have tide predictions on them?
There are any number of WWW sites that have tide predictions on them. Due to the rapid growth of the WWW we presently do not attempt to keep up with the other sites that have tide predictions on them; nor do we presently verify the accuracy of their predictions. Caution should be exercised when using tide predictions from other WWW sites. Some obtain their tide predictions from our office; others obtain their predictions from sources which may or may not be accurate or up to date.
BackWhat is the difference between "Tide Charts" and "Tide Tables"?
"Tide Charts" and "Tide Tables" are actually two different products.
"Tide Charts" refer to a series of maps which show the water levels through out a bay or estuary at a particular point in time. These maps normally show the water levels on an hourly basis after high tide. "Tide Charts" are only available for a few locations around the U.S.
"Tide Tables" refer to tidal predictions tables which show the daily high and low tide predictions for a particular location. "Tide Tables" can be generated for more than 3000 locations around the U.S. For more information on obtaining "Tide Table" predictions, please read the next few Frequently Asked Questions.
What are the "Perigean Spring Tides"? Do they cause coastal flooding
The question of "Perigean Spring Tides" has been one that our office has been required to answer on numerous occasions over the years. The whole issue of coastal flooding during the "perigean spring tides" stems from a misunderstanding of the information presented in a book by Fergus J. Wood, published in 1978.
Since the moon is the primary source of the gravitational forces which cause the tides. The proximity of the moon in relation to the earth does have an effect on the range of the tides at any given time. In each of it elliptical orbits, the moon reaches a perigee during which it is at it's closest point of approach to the earth. During these periods, there will be a slight increase in the average range of tides. Additionally, twice each month, around the times of the new moon and full moon, when the earth, sun, and moon are nearly in line, there is an increase in the average range of the tides. These are called "spring tides". Three or four times a year, the occurrence of a new or full moon will coincide with the perigee of the moon, which Mr. Wood has termed the "perigean spring tides". The increases in the range of the tides is seen by a slightly higher than average high tide, as well as a slightly lower than average low tide.
The difference between the "perigean spring tides" and the normal tidal ranges for all areas of the coast is small. In most cases the differences is only a couple of inches. The worst case that we have found occurs in certain areas of the Alaska coast where the range of the tide was increased by approximately 6 inches. But when you consider that these areas have a average tidal range of more than 30 feet, the increase is but a small percentage of the whole (less than a 2% increase).
In Mr. Woods book, he examines the occurrences of coastal flooding though history. What he discovered is that coastal flooding did occur when there was a strong onshore winds, such as a hurricane or nor'easter, which occasionally occurred at the same time as a "perigean spring tide".
The problem has been that a number of people have misinterpreted the information presented in this book to mean that coastal flooding would occur whenever these "perigean spring tides" occur. This has lead to articles published in various media sources which incorrectly predict wide spread coastal flooding at the times of these "perigean spring tides", causing needless concern and in some cases, panic.
Most people who live along the coastline know that coastal flooding can occur whenever there is strong onshore winds, if there is a "perigean spring tide" or not. Additionally, this flooding will be only slightly worse if the storm strikes around the time of high tide rather than around the time of low tide.
But in ALL cases, it is the onshore, storm winds which cause the coastal flooding; not the tides. Coastal flooding is the result of meteorology (the weather) not astronomy (normal tidal fluctuations). All astronomical considerations are accounted for in the official NOS tide and tidal current predictions, available on our web site; as well as printed tables distributed and sold by private publishers.
Are there tides in the Great Lakes?
The water levels of the Great Lakes have long term, annual, and short term variations. Long term variations depend on the precipitation and water storage over many years. Annual variations occur with the changing seasons. There is an annual high in the late spring and low in the winter. These changes occur at a rate which can be measured in feet per month.
True tides, changes in water level caused by the gravitational forces of the Sun and Moon, do occur in a semi-diurnal pattern on the Great Lakes. The investigations of the U.S. Coast and Geodetic Survey indicate that the spring tide, the largest tides caused by the combined forces of the Sun and Moon, is less than 2 inches (5cm) in height. These minor level variations are masked by the greater fluctuations in lake levels produced by wind and barometric pressure changes. Consequently, the Great Lakes are considered to be essentially non-tidal.
Other factors may create quite large fluctuations of lake levels, but for only short periods of time lasting from minutes to several days. The two most dramatic are storm surge and seiche.
Storm surge is a sudden, and often unexpected, rise in lake level associated with a rapid change in atmospheric pressure, a pressure jump, or a storm wind over a short period of time. If high winds are steady for a long period, several hours, a change in water level will occur known as wind set-up. Once the winds cease or shift direction, a standing wave called a seiche may occur. This is very similar to the wave created by sloshing water in a bathtub. The lake surface will oscillate from higher to lower with decreasing amplitude over a period of several days. It is this oscillating water level that is most often confused with a tide as that the period of the oscillation in some lakes is very similar to the period of the tides.
In summary:
Water levels in the Great Lakes change not because of the tides, but because of meteorological
effects imposed on the longer term changes in the amount of water in the lakes.
For current and historic levels in the Great Lakes, see the Water Level Observations or Great Lake Online sections of our web site.
For additional information on lake level changes, see the US Army Corp of Engineers Great Lakes Hydraulics and Hydrology web page.
Where can I find information on the 100-year, 50-year, 10-year tide levels?
Although these values are often referred to as "tide levels" for coastal areas which experience tides, they are more appropriately associated with flood heights and not the tides. Observational data from our office is often used to determine these values, but they are derived values which are developed and published by other agencies.
Some sources for this information include:
Federal Emergency Management Agency (FEMA)
U.S. Army Corp of Engineers
I am trying to set my clock/watch to predict the tides. The instructions ask for the Lunitidal Interval, how can I find that?
The Lunitidal Interval is the average time difference between when the moon passes over the local or Greenwich meridian and the following high or low tide. Generally, the manufacturers of such items use the Local Interval for their calculations. Our office does not track or maintain the Local Intervals, we calculate and track the Greenwich Intervals for various locations. This information can be found in the "Water Level Observations" section of our web site under the Accepted Datums heading. You will need to use the High Water Greenwich Interval.
The Greenwich Intervals we provide can be converted to the Local Interval using the following formula:
Local Interval = Greenwich Interval - (0.069 * L)
Where L is the longitude for the location in degrees. West longitudes are positive; East longitudes are negative.
Some companies will require the Local Interval to be a positive number.
You can convert a negative interval to a positive by adding 12.42 to the result.
Thus if your interval calculated to be -4.11, you could also use 8.31 (-4.11 + 12.42 = 8.31)
How can I find information on the range of the tides?
Within the Water Level Observations section you will find a heading labeled Accepted Datums. In this area you will be able to obtain datum values for water level stations. The two commonly used tidal ranges are listed for each station. These ranges are the Mean Tidal Range (MN) and the Diurnal Tidal Range (GT).
It appears that the range of the tides gets larger the further the location from the equator. What causes this?
If you only look at a few locations, this may seem to be true; but it is not the case. There are literally hundreds of locations in the extreme north and south latitudes which have small tidal ranges, and a number of stations closer to the equator which have large tidal ranges. For example, Korea is at roughly the same latitude as most of the U.S. coast. There are numerous stations in Korea which have a tidal range of more than 20 feet. There are also a number of locations very near the equator which have a tidal range of about 15 feet.
The tidal range of a particular location is dependant on a lot of different factors. One of which is the configuration of the coastline. For example, let's examine the southern coast of Alaska and British Columbia. The configuration of this coastline is very similar to a funnel with the narrow end at Cook Inlet. Since the tides travel as a wave across the oceans, this type of configuration tends to accentuate the wave at the narrow end of the funnel. This is part of the reason for the large tidal ranges in this area. If you look at the tidal ranges for stations on the Bering Sea, outside this funnel but at the same latitude, you will find a tidal range of 5-7 feet. A fairly average tidal range.
Another factor is the size of the ocean basin which the tides have to build in. The Pacific Ocean is by far the largest of the world's oceans. This means that the moon's gravity has a large area of water to work on, thus its effect will tend to be greater. Compare this to stations in the Baltic Sea. Many stations in the Baltic are as far north as any station in Alaska. However, due to the small size, and shallow depth of the ocean basin, the tidal ranges in this area are relatively small.
Are the stations presented on your WWW site the only ones that tide predictions are available for?
The stations shown on our WWW site are actually the NOS Tidal Reference Stations for the U.S. There are more than 3000 secondary stations around the U.S. for which we can make tide predictions. You may now calculate the predictions to these secondary stations by applying the tidal differences and other constants to the reference stations. Make a Tide Prediction
The "Tidal Differences and Other Constants" page and the Reference Station tide predictions on your web site are difficult to read. Why is the font so small?
The Reference Station tide predictions and the Tidal Differences pages are designed so that they will fit on the screen of the 800x600 resolution monitor without having to scroll right and left. This also allows the page to be printed without cutting off any information. If your monitor has a higher resolution than 800x600, the print will appear small. You can change the appearance on your screen by temporarily changing the font of your browser.
How can I get tide predictions for next year or any year?
Daily tide predictions for the present calendar year are available for more than 3000 locations around the U.S. in the Tide Predictions section of our web site. The predictions presented in this section of our web site are updated in late October or November to covering the next calendar year. For example, the predictions for 2003 will be added to the web site in October or November of 2002.
Daily tide prediction for a single calendar month, for dates outside the one year presented on our web site, can be obtained via e-mail from: Tide.Predictions@noaa.gov. Subsequent requests for additional months of predictions will be subject to the fee for custom predictions described below.
Hourly tide predictions for any station which has accepted harmonic constituents, about 200 of the 3000 listed in the "Predictions" section of our web site, can be generated directly from the Predicted Water Level Data page of our web site. These predictions consist of either hourly heights or 6-minute interval heights of the tides. The data can be provided graphically or in a spread-sheet style of format.
Daily tide predictions of more than one month in length (other than the one year presented) are not available through the web or E-mail 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, please include the following information:
Your Full Name
Your Full Mailing Address (NOT e-mail)
Your Phone Number (Including Area Code)
The type of predictions you want (Tides or Tidal Currents)
The Location(s) for which you want predictions
The dates for which you want predictions
The Format and Options you want included (see next question below)
- AM/PM or Military Time (24 hour)
- With or Without Daylight Savings Time
- Standard, International, or Manuscript Format
Since Standard and Manuscript formats can be provided on hard-copy (paper) or on diskette, when requesting either of these formats please indicate which media you want provided. If no preference is listed, a paper copy will be provided.
Please Note: We are only able to make tide predictions for specific locations where there has been a NOS tide data collected. Please refer to the Tide Predictions section of our WWW site for a listing of the stations which are available.
The tide predictions will be sent to the mailing address you provide.
**** PLEASE NOTE ****
There is a fee for long term tide
predictions. This fee is normally $35 for a calendar year of predictions at one
location; each additional year or location is $10.
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What formats are tide predictions available in?
Tide predictions are available in several different formats.
International Format - This format is an electronic, ASCII file which provides time and height of tide information 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 EASTPORT, ME, April, 1997 shows the predictions in 24-hour clock and in Eastern Standard Time. This format can be modified to show AM/PM Time and Daylight Savings Time.
90 2285 1 497 428 18.6 1101 0.7 1704 17.8 2328 1.5 9999 99.9 9999 99.9 1 90 2285 2 497 532 18.8 1204 0.4 1808 18.2 9999 99.9 9999 99.9 9999 99.9 2 91 2285 3 497 33 0.9 636 19.2 1307 -0.2 1911 19.0 9999 99.9 9999 99.9 3 91 2285 4 497 136 0.0 739 20.0 1407 -1.1 2010 20.1 9999 99.9 9999 99.9 4 91 2285 5 497 235 -1.2 838 20.9 1504 -1.9 2106 21.1 9999 99.9 9999 99.9 5 91 2285 6 497 331 -2.2 933 21.6 1557 -2.6 2158 22.0 9999 99.9 9999 99.9 6 91 2285 7 497 424 -3.0 1025 21.9 1648 -2.8 2248 22.4 9999 99.9 9999 99.9 7 91 2285 8 497 514 -3.3 1115 21.9 1737 -2.7 2336 22.3 9999 99.9 9999 99.9 8 91 2285 9 497 604 -3.2 1204 21.4 1825 -2.1 9999 99.9 9999 99.9 9999 99.9 9 90 2285 10 497 24 21.9 653 -2.6 1253 20.7 1914 -1.2 9999 99.9 9999 99.9 10 90 2285 11 497 113 21.1 742 -1.7 1343 19.7 2003 -0.2 9999 99.9 9999 99.9 11 90 2285 12 497 203 20.1 832 -0.7 1434 18.6 2054 0.9 9999 99.9 9999 99.9 12 90 2285 13 497 255 19.0 924 0.4 1528 17.7 2147 1.8 9999 99.9 9999 99.9 13 90 2285 14 497 350 18.0 1018 1.3 1624 17.0 2243 2.5 9999 99.9 9999 99.9 14 90 2285 15 497 448 17.4 1114 1.9 1723 16.6 2341 2.8 9999 99.9 9999 99.9 15
Standard Format - This format is available in hardcopy and an electronic, ASCII file which provides time and height of tide information for a single location in a page readable format. The following example for EASTPORT, ME, April, 1997 shows the predictions in AM/PM Time and has been adjusted for Daylight Savings Time.
Eastport, Maine T.M. 75 W. Tide Predictions (High and Low Waters) April, 1997 NOAA, National Ocean Service Standard Time Day Time Ht. Time Ht. Time Ht. Time Ht. 1 Tu 428am H 18.6 1101am L 0.7 504pm H 17.8 1128pm L 1.5 2 W 532am H 18.8 1204pm L 0.4 608pm H 18.2 3 Th 1233am L 0.9 636am H 19.2 107pm L -0.2 711pm H 19.0 4 F 136am L 0.0 739am H 20.0 207pm L -1.1 810pm H 20.1 5 Sa 235am L -1.2 838am H 20.9 304pm L -1.9 906pm H 21.1 Daylight Saving Time begins at 0200 6 Su 431am L -2.2 1033am H 21.6 457pm L -2.6 1058pm H 22.0 7 M 524am L -3.0 1125am H 21.9 548pm L -2.8 1148pm H 22.4 8 Tu 614am L -3.3 1215pm H 21.9 637pm L -2.7 9 W 1236am H 22.3 704am L -3.2 104pm H 21.4 725pm L -2.1 10 Th 124am H 21.9 753am L -2.6 153pm H 20.7 814pm L -1.2 11 F 213am H 21.1 842am L -1.7 243pm H 19.7 903pm L -0.2 12 Sa 303am H 20.1 932am L -0.7 334pm H 18.6 954pm L 0.9 13 Su 355am H 19.0 1024am L 0.4 428pm H 17.7 1047pm L 1.8 14 M 450am H 18.0 1118am L 1.3 524pm H 17.0 1143pm L 2.5 15 Tu 548am H 17.4 1214pm L 1.9 623pm H 16.6
Manuscript Format - This format is available in hardcopy and electronic PostScript file, which provides time and height of tide information 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.
Example for EASTPORT, ME, April-June, 1997 .
How accurate are the predictions?
The accuracy of the tide predictions is different for each location. Periodically we do a comparison of the predicted tides vs the observed tides for a calendar year. The information generated is compiled in a Tide Prediction Accuracy Table. We work to insure that the predictions are as accurate as possible. However, we can only predict the astronomical tides, we cannot predict the effect that wind, rain, freshwater runoff, and other short-term meteorological events will have on the tides.
In general, predictions for stations along the outer coast are more accurate than those for stations farther inland; along a river, or in a bay or other estuary. Inland stations tend to have a stronger non-tidal influence; that is, they are more susceptible to the effects of wind and other meteorological effects than stations along the outer coast. An example of an inland station which is difficult to predict is Baltimore, Maryland. This station is located at the northern end of Chesapeake Bay. Winds which blow along the length of the bay have been known to cause water levels to be 1-2 feet above or below the predicted tides.
Stations in relatively shallow water, or with a small tidal range, are also highly susceptible to meteorological effects and thus difficult to accurately predict. At these stations, short-term weather events can completely mask the astronomical tides. Many of the stations along the western Gulf of Mexico fall into this category. An example is Galveston, Texas. This station is in a bay which is relatively shallow and has a small opening to the sea. At this station it is possible for meteorological events to delay or accelerate the arrival of the predicted tides by an hour or more.
Where can I get tide predictions for locations outside the United States?
Due to an agreement through the International Hydrographic Organization, we
receive annual tide predictions for countries outside the United States every
year. Therefore, you can obtain tide predictions for many locations around the
world for the current calendar year by contacting our office. There are some
few locations outside the United States that we can make tide predictions for
beyond the current calendar year, but in most cases you will need to contact
the Hydrographic or Oceanographic Agency in that
country.
NOTE: For countries that have web site, a link is also provided.
You can contact our office at (301) 713-2815 between 7AM-3PM
Eastern Time. You may also request 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, please include the following information:
Your Full Name
Your Full Mailing Address (NOT e-mail)
Your Phone Number (Including Area Code)
The type of predictions you want (Tides or Tidal Currents)
The Location(s) for which you want predictions
The dates for which you want predictions
The format and options you want included (see question above )
The tide predictions will be sent to the mailing address you provide.
**** PLEASE NOTE ****
There is a fee for long term tide
predictions. This fee is normally $35 for a year of predictions at one
location; each additional year or location is $10.
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How can I get a copy of the program that you use to make tide predictions?
Our office does offer copies of the program that we use to make tide predictions for the NOS Tidal 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 tide predictions for different time periods. A copy of the tide 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 by sending e-mail to our address: Tide.Predictions@noaa.gov. If you elect to submit your request via e-mail, please 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 tide prediction program
The Location(s) you want control files for
**** PLEASE NOTE ****
There is a $39 fee for a copy of this
program. The program comes with the control file for one NOS Tidal Reference
Station of your choice and copies of the "Manual of Harmonic Analysis.." and
"Computer Applications to Tides..." listed below. Harmonic constituents for
additional stations are available at a cost of $10 each.
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I want to develop my own program to predict the
tides.
What information can you provide me with which will help me do
this?
There are a number of products/services that we can offer you.
1) "Our Restless Tides" - A booklet which describes the astronomical forces which cause the tides in terms that can be understood by the average student. (cost $5)
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. (cost $22)
3) "Computer Applications to Tides in the National Ocean Service (Supplement to Special Pub 98)" - A booklet which describes the methods of predicting tides that are used by NOS. The booklet contains sample algorithms for tidal data analysis and tidal predictions. (cost $15)
4) Tide Prediction Package - The predictions package includes a copy of items 2 and 3 listed above. The package also includes a limited copy of the tide prediction program (NTP4) used by NOS to generate tide 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 tides are to be generated for. This control file has to be altered each time that tides 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 that harmonic constants are available for; the NOS tidal reference stations (those listed on our WWW site). The package comes with a control file (harmonic constants) for one Tidal Reference Station of your choice. Please include your choice of station with your request.(cost $39)
5) Tidal Harmonic Constants - copies of the tidal harmonic
constants, provided in hardcopy or in NTP4 control file format, are available
for 75 Tidal Reference Stations.
(cost $10 each)
6) Tide Table 2 Files - These are a list of the NOS secondary
stations whose tide predictions are generated by applying time and height
adjustment to tide predictions. There are two table 2 files for the U.S.
- Tide Tables for the East Coast
- Tide Tables for the West Coast
(cost $88 each)
**** PLEASE NOTE ****
As the bays and estuaries change due to
natural or artificial processes (shoaling, erosion, dredging, construction) the
tides for the area can be effected. The tidal harmonic constants and table 2
corrections do change as more recent data is received and analyzed.
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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, please 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.
A few years ago I was able to obtain books with the Tide and Tidal Current Predictions for the entire US coast from the Government Printing Office. I do not seem to be able to find them now. Are they still being produced by the Federal Government and how can I get one?
The National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), due to reduced funding, ceased printing the annual Tide and Tidal Current Tables. The role of NOS with regard to the publication of these Tables was redefined to be that of maintaining and updating the tidal predictions database from domestic and international sources and generating the annual predictions and associated information. Beginning with the 1996 edition the actual printing, distribution, and sale of these Tables has been assumed by private sector printers.
The titles of the NOS publications affected are:
Tide Tables:
- East Coast of North and South America including Greenland
- West Coast of North and South America including the Hawaiian Islands
- Central and Western Pacific Ocean
- Europe and West Coast of Africa including the Mediterranean Sea
- Supplemental Tidal Predictions - Anchorage, Nikishka, Seldovia, and Valdez, Alaska have been incorporated into the Tide Tables, West Coast of North and South America
Tidal Current Tables:
- Atlantic Coast of North America
- Pacific Coast of North America and Asia
Many local publishers and printers around the country publish regional and localized tide and tidal current predictions in booklet, calendar, and other formats. The data printed in these local and regional publications is, in many cases, obtained directly from NOS. For availability of localized prediction tables consult marinas and marine supply companies in your area. Since there are literally hundreds of such publications, we cannot list them.
As of this date, three publishing firms are printing complete east and west coast tide and tidal current predictions for US ports and coastal areas - ProStar Publications, Thomas Reed Publications, and the International Marine Division of McGraw Hill. As additional companies advise NOS of their publication of complete NOS tide and tidal current data for either east and/or west coast, they will be added to this listing.
