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The Oceanographic
Products and Services Division website allows you to predict coastal
tides.
- Follow these steps to predict tides on your favorite part of the coast:
- Using an atlas, identify your favorite spot on the U.S. coast.
- Visit the "Make
a Tide Prediction" webpage.
- In the left column, U.S. coastal states will be listed. Choose
your U.S. state (or coast in U.S. territories).
- You will see a list of coastal areas in that state or territory.
Click on the station located closest to your favorite coastal spot.
A graph of data will show predicted (blue) versus observed (red) water
levels (WLs). The green line shows the difference between these WLs. If
the predicted and observed WLs matched exactly, then the green line would
equal zero over the time period shown.
To see "Tide Predictions" for this station, click on the button
in the lefthand column. You can change the start and end dates using the
"pull down" menus at bottom.
Data tables are commonly used to predict tides. Click
here to see an example of how to use data tables to
predict coastal tides.
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- Click
here to access the July 1998 data for the Portland, Maine reference
station. Note that, in this example table, high tide data are shown
in red.
- Did everyday in July 1998 have two low tides?
Two high tides?
- Randomly choose five dates in July 1998. If
those dates had two high tides, what was the difference between the
higher high tide and the lower high tide?
- Was the variation between subsequent high
tides greater than, less than, or about 2 feet?
- Does this variation in the two daily high
tides put Portland Maine's coast into the diurnal, semidiurnal
or mixed tide type?
- Click
here to see the water levels associated with these tide
types.
- The DIFFERENCE in the height
between consecutive high and low water levels is known as the tidal
range.
- Is the date with
the highest tidal range called a spring
tide, a neap tide, or neither?
- For
the July 1998 Portland Maine data, find the date / time with the
highest tidal range:
- Begin by finding the relatively high values
for high tide (in this case, these values are greater than 10.5
feet)
- Then look at the values for low tides
before and after these relatively high tides (in this case, the
values are LESS THAN ZERO).
- The tidal range is the difference been
these numbers.
- For example, on Saturday,
July 11th the high tide at 12:31 A.M. was 10.5 ft
- The next low tide (at 6:54 A.M.) was
-.5 ft
- The tidal range for this example is
11 ft [= 10.5 - (-.5)]
- [By the way, this is NOT the
highest tidal range for July 1998!]
- To which lunar phase do you think the
date / time of the highest tidal range corresponds?
- Check your answer against a source that
has lunar phase information.
- For example, visit the U.S. Naval Office's
"Virtual
Reality Moon Phase Pictures" website.
- Enter data to get a lunar phase image
for:
- The current time (updated every
four hours); or
- Any hour for dates from 1800 A.D.
to 2199 A.D.
- Be sure to choose "Eastern
Time" for this example.
- Did the highest high tide match with the
lunar phase you predicted?
- Can you guess why or why not?
- If possible, compare your "favorite spot's"
tide prediction to that from a local newpaper.
- Does your prediction match theirs?
- How do you suppose they predict tide levels?
- Consider the data tables used to predict tides.
- Knowledge of the times, heights, and extent
of inflow and outflow of tidal waters is of important for many maritime
activities.
- Can you list activities that might benefit
from tide predictions?
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