Frequently asked questions
Where can I find more information about tide levels and datums?
All our published tide heights and the heights shown on the TideFlash graph are relative to the zero height
used in official marine charts. This zero height is known as the datum.
Standard ports have a physical marker that can be used to relate the datum to a real world height.
For instance, Auckland has a bronze plaque which is 5.233 metres above the datum. This plaque is
set in concrete in the road at the entrance to Captain Cook Wharf.
Land Information New Zealand (LINZ) - who are the suppliers of our tide information - have information
about datums around New Zealand, and an explanation of how tide heights are defined, on their
Where can I find tide graphs for other parts of the world?
For the Pacific Islands, United States of America, Carribean, and Central America,
go to this website.
For other parts of the world, you'll need to use a search engine.
What causes tides to occur?
Tides are caused by the gravitational attraction of the sun and moon upon the earth's oceans, combined with the
daily rotation of the earth. The motion of the sun. moon, and earth are entirely predictable, and so we can
predict tides well into the future.
Unfortunately, a large number of factors make the prediction process quite complex. As we demand more
and more accuracy in the times and heights our predictions, so the process becomes more complex.
For any given place, factors that affect tide heights and times include the location of the place on the globe,
the depth of the sea, the shape of the coastline, the presence of rivers, bays and inlets, and other nearby
land masses. Tides are also affected by non-predictable factors such as wind and the barometric pressure.
Further information may be found at these sites:
How should I interpret the graph?
The graph shows the tide height for all times over
a 24-hour period. The height is relative to Chart Datum which is the zero depth
for marine charts. The slope of the curve shows the strength of tidal flows;
a steep slope means strong currents, a flat slope (tops of peaks and bottoms
of troughs) means slack water. High tide occurs at the top of a peak on the
graph, and low tide occurs in the centre of a valley.
Note: The vertical
scale is calculated on the fly and it may change as you look at different places
or months, thus a curve that "looks big" may in fact be considerably
smaller than another that appears smaller, and vice-versa.
Can I find out the exact height for a given time?
Click anywhere on the graph for a display of the
tide height for any given time. You can also find the time and height of a high
or low tide by hovering the mouse pointer near a peak or valley.
My computer won't remember my default place
The Tide Graph applet puts a "cookie" on your computer
which contains the name of the last place you selected. If you have disabled cookies in
your browser or you have cleared the cookie files from your computer, then the
applet will not show a graph when it starts.
The cookie will remain on your computer for 100 days. If you don't visit the graph
within that time, then your last place will not be remembered.
Can I make a bookmark for a particular place?
Yes, with a little craftsmanship. The normal URL for the
tide graph is http://ofu.co.nz/webgraph and to specify a place you must add ?p= to the end,
followed by the name of the place, spelt correctly and with correct capitalization. Replace any
spaces in the names with plus signs. For instance,
Enter the URL into your browser and check the correct page is displayed, then simply bookmark it in the usual way.
How can I find out tides for a place that is not in the dropdown list?
You can't do this easily, though often a nearby
place will be close enough. Click the place you want on the map, and look at the
first few entries in the resulting list. These will be the nearest places we have data for.
One method is to find a place either side of you desired place and split the difference in
tide times and heights. Places within estuaries, inlets and rivers will be affected by the
flow from the river and may not be easily calculated this way.
I would like a tide graph for a place you don't list
Send us an email. We may have the information,
but if not then we are simply unable to help. Obtaining the information
for drawing a graph is a complex process and all places for which we have data
are present in the graph's list of ports. We will be adding more as data becomes
Can I use your graph on my website?
We are open to a variety of ways to do this. The
easiest is for you to add a link to our Tide Graph, and you are welcome to do
this, but bear in mind it is useful in New Zealand only.
If you want the applet directly on your web site then an arrangement is possible,
and it is possible to configure the tide graph for almost any coastal region
on the planet, if data is availabe.
Also please see our Linking Policy.
The graph says "Tide data not available". What's wrong?
Ensure that your Internet connection is still up
and running, and that you are not using an Ad blocker.
If you get this message repeatedly then the data you are requesting
may not be available on our website. Let us know with an Email to our
- and please remember to tell us which month and place you are having problems
Are the tide graphs accurate?
Tide heights and times can be affected by several
factors, the two most common being the air pressure (low air pressure means
higher tides) and by winds (a strong onshore wind will increase the height and
bring the time forward, and an offshore wind will do the opposite). After considering
these factors, if you feel our data is consistently wrong then please
contact us. We put a lot of effort into getting the data correct, but inevitably
the occasional error does slip through (and they not all of our own doing, I
The quality of information varies between places. For some places
we have no height information, so we draw the graph using the heights for the nearest
standard port. The times for high and low tides will generally be quite accurate but
the true heights of the tides may vary from those shown on the graph.
How can I print the TideGraph?
Simply use the print function of your browser.
What's the story with Daylight Saving time and Time Zones?
The graph is normally corrected for daylight saving,
so you should not need to do this manually. We assume a New Zealand Time Zone
and Daylight Saving regime so even if you are in another country the times shown
will be New Zealand times. However, the current time marker will be in the wrong place if
your computer is showing the wrong time or is showing the correct time for some other
time zone or country. We do not recommend using the graph from outside New Zealand.
When NZ time changes to and from daylight saving time
there will be a jump in the tide height, and since there is no correct way to
show this on the graph (between 2am and 3am) you will have to use your head
and figure out the correct height yourself.
Please Note: A small percentage of computers in certain configurations may fail
to provide the TideFlash graph with Daylight Saving information. If this is the
case then you must apply Daylight Saving corrections yourself. Click on the graph and the
time and height of the tide will be displayed in the caption. Following the time you wiill
see either nzst (New Zealand standard time), or nzdt (NZ Daylight time).
If nzst appears while Daylight Saving is in force, then you must add one hour to all times yourself.
I only see a broken image icon, or a blank space, in my browser.
What could be wrong?
- Check in your browser options, that you have allowed scripts to run. A good
- Some firewalls and advertisement blockers will interfere
with the page's access to files on the website. Most often you will see
an error message, "Tide data not available", but the effects could
Why can't I get tides more than a month or two in the future?
We publish and sell a large range of products giving
tide times and graphs well into the future for most parts of New Zealand (and
a number of other countries) and we suggest you purchase one suitable for your
purposes. If we make this site too
durned good, you won't buy any of
our products. Visit your local bookshop or take a look at the
OceanFun Publishing Ltd shop.