JGS wrote:
On Sun, 19 Dec 2004 17:43:05 -0500, Jeff Morris
wrote:

Snipped

See:
http://www.ndbc.noaa.gov/station_page.php?station=45005

Look at the data significant wave height:
http://www.ndbc.noaa.gov/images/climplot/45005_wh.jpg

Looks like it came close to a 12 footer at least on one occasion. Perhaps in
the Central Basin it may have reached 12'.

But you're right, a 12 footer seems quite rare if it ever did quite make it.


If you look at the text data you'll see that that the "significant wave
height" only reached 4 meters (13 feet) once in a 20 year period.
However, it did get over 3 meters several times a year, and over 2
meters numerous times. Of course, the worst weather is in the Spring
and Fall (and the the buoy is pulled in the Winter) so the Summer sailor
will not likely see these conditions.

"Significant wave height" is the average of the higher third of all
waves, measured over the course of an hour. If that is 3 meters, then
the average of the highest tenth of all waves would be about 4 meters.
Thus, many individual 12 foot waves have happened, though usually no one
was there to witness them.

Anyone who goes out when the wave height is 6 feet (as it was the last
time I was on Lake Ontario) will likely see some 8 footers and maybe, if
they're out all day, a few 10 footers.

BTW, in a hurricane significant wave height will get much larger - 10
meters would easily be possible.



Jeff

Thanks for that clarification. The significant wave height data did not have
a clear legend for interpretation. (I didn't poke through the site too much)
I appreciate your time to explain it.

Wally is right though, the chop sure can get rough and my dear wife doesn't
like it then. Guess I am, and will always be, a "fair weather" boater.


I noticed elsewhere on the site that they used 20 minutes as the
sampling period, not one hour.

The concept of "the average of the higher third" is a little hard to
understand. I find it interesting that it sort of corresponds with the
old adage "the highest wave is the seventh."