The publication of full daily tide predictions is necessarily
limited to a comparatively small number of stations. These
stations are referred to as "reference stations".
Tide predictions for more than 3000 other locations can
be obtained by applying certain differences to the daily
tide predictions for the reference stations.
These pages provide a listing of the more than 3000 "subordinate
stations" for which such predictions can be made, the
differences or ratios to be used, and a link to the appropriate
reference station. The stations in the listing are arranged
in geographical order to make it possible to find stations
which are available for an area you are interested in.
Caution:
The time and height differences and ratios are derived from
a comparison of simultaneous tide observations at the subordinate
station and it reference station. Because these figures
are constant, they may not always provide for the daily
variations of the actual tide, especially if the subordinate
station is some distance from the reference station. Therefore,
although the application of time and height differences
will generally provide reasonably accurate approximations,
they cannot result in predictions as accurate as those listed
for the reference stations which are based on much larger
periods of analysis.
Time Differences:
To determine the time of high and low tide at any station
listed in this table there is given the columns headed "Time
Differences"in which the hours and minutes to be added
or subtracted from the time of high or low tide of the reference
stations. A plus sign (+) indicates that the tide at the
subordinate station occurs later than at the reference station
and the difference should be added; a minus sign (-) indicates
that it is earlier and should be subtracted.
To obtain the tide at a subordinate station on any date,
apply the difference to the tide at the reference station
for that same date. In some cases, however, to obtain an
AM tide it may be necessary to use the preceding day's PM
tide at the reference station or to obtain a PM tide it
may be necessary to use the following day's AM tide. For
example, if a high tide at a reference station occurs at
0200 on July 17, and the tide at the subordinate station
occurs 5 hours earlier, the high tide at the subordinate
station will occur at 900 PM on July 16. For the second
case, if the high water at a reference station occurs at
1000 PM, and the tide at the subordinate station occurs
3 hours later, then high tide will occur at 1:00 AM on July
3 at the subordinate station.
The results obtained by application of the time differences
will be in local time for the subordinate station. The necessary
allowances for the change in date when crossing the international
date line, or for different time zones have been included
in the time differences listed.
Height Differences:
The height of the tide, referred to the datum of nautical
charts, is obtained by means of the height difference or
ratios. A plus sign (+) indicates that the difference should
be added to the height at the reference station, and a minus
sign (-) indicates that it should be subtracted. For most
stations, use of a predicted height difference would give
unsatisfactory predictions. In such cases they have been
omitted and one or two ratios, indicated by an asterisk
(*), are given. To obtain the height of tide at the subordinate
station in these cases, multiply the height of tide at the
reference station by the ratio listed. The result is normally
rounded to the nearest .1 foot.
For some subordinate stations there is given, in parentheses,
a ratio as well as a correction. In those instances, each
predicted high and low water at the reference station should
be first multiplied by the ratio and then the correction
is added or subtracted from each product.
