G. Niblock on the L41 TipSUP Noserider. Photo: J. Chandler

Wednesday, July 9, 2008

Nearshore Buoy Data Analysis

"He not busy being born, is busy dieing." Bob Dylan (It's Alright Ma, I'm Only Bleeding)

One of the reasons I started a surfer's journal in a looseleaf spiral notebook almost a dozen years ago, was to learn more about the ocean, the waves and when, where and why there would be good surf at any given time. Last year, after a friend gave me a good quality, digital SLR camera, I added pictures to the journal and started keeping it online. Keeping the journal online has facilitated my ability to learn because of all the many and rich resources there are (for free!) on the internet. I'm "self taught" only in the sense that I haven't enrolled in any specific classes to learn about what I blog about. But in reality I have many teachers both online and in person.

Learning one thing has always led to another. Each time I learn something, it is a stepping stone to something else. In that vein, today's post is about using data from a secondary buoy source (the "nearshore" buoy), to confirm the presence of a swell, and analyze the data viz a viz the primary buoy source (the "farshore" buoy). My ultimate goal has always been to learn enough to analyse the data and KNOW there are waves. When I get to my spot, I don't want to waste any time checking it out. I want to KNOW that there's waves, and go surf them...sight unseen.

This recent WNW swell is a good one to look at, because it is so unusual to have groundswell that originates from the NPAC in the summer months. So it contrasted nicely with the low energy, southwesterly "background" swell that has been in the water for a while. The charts from the nearshore buoy at right depict three values: swell height; swell period; and swell direction. I want to know how they compare to the values depicted on the charts for the "farshore" buoy. I already know that in order to get an energized groundswell or even a good windswell, the data from the farshore buoy should read at least in double digits. That is, 10 feet (wave height) at 10 seconds (swell period) minimum (or so). The closer the values are to 10 at 10, the better the surf will be. I've also found that it is more accurate and reliable to look at the swell height number (SwH) for wave size, than the significant wave height (WVHT) number.

The nearshore buoy almost always shows much lower swell height readings, perhaps that is because it is closer to the shore and the effects of the swell traveling over open ocean and then making landfall, reduce the wave size and (but not necessarily) the swell period. By checking out the charts I can see that my surf on Monday, July 7th, occurred during what I would call the peak of the swell. The tide was right for the surf spot, and the swell was big enough and had the energy to produce consistent chest to head high waves for a number of hours. (The peak hours corresponded to the best tide heights for this surf spot, i.e. the best tide for this spot is between X feet low and X feet high.)

By comparing the farshore numbers (average 10.6 feet at 12.1 seconds WNW) to the nearshore averages for the affected hours, then I should be able to confidently predict that swell is in the bay, and delivering the goods. Are we having fun yet? I am!

Therefore, if the farshore buoy needs to be showing data of 10 feet at 10 seconds, the nearshore buoy should show readings of at least 4.5 feet at 12 seconds (on average) to expect solid surf in the line-up.

All the above is generally reliable with the caveat that a long interval swell period trumps everything. I'd trade a 10 foot swell at 12 seconds for a five foot swell at 18 seconds any day. As a matter of fact, the recent south swells were delivering high energy head high waves with the buoys reading 3.5 feet at 17 seconds. When you those kinds of numbers, start salivating!

Someone once accused me of being an "armchair scientist" and if that means that I'm just a total novice, "guessing" at outcomes based upon purely subjective theories, then I plead guilty. But by testing and applying the data, I've found that I can rely upon my conclusions most of the time. And by analyzing the data and comparing it to the reality of nature, I've grown much closer to, and have a much greater appreciation of this amazingly miraculous creation we live on.

Life is good.

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