I interpret these charts as telling me we have a 12 second swell on average (with a few longer period ones thrown in) and its mainly coming from the SSW direction. 180 is direct south swell and 270 is west so 203 is pretty much south with a little bit of west in it. The single dots are just points in time that the buoys take readings. Think of them as discrete points - a single point in time. No real need to join them up - just take an overview of them and calculate yourself a rough average. A few degree's is not going to make much difference. Where it gets interesting is when the buoys are picking up to distrinctly different swells at once. Eg: a south swell and a new North East on its way. The good tihng about this chart is that its showing you that the period is increasing as we move forward. A very positive thing to see!!!!

Oliver,

All you need to look at is that the swell direction over the time period logged is between 193 and 213 deg.

180 deg is directly south
225 deg is directly south west
270 deg is directly west

So the swell direction vector was SSW and varied in direction by 20 degs.

Phill

Kagey said...

Period is everything in determining size and power of shoreline surf. Long period swells (like 13 seconds) will pack more size and more punch when compared to a short period wind swell (like 4 seconds). And for your information my local has a wave period of 3 tomorrow...

Could I interpret then that the time period relates to how the bouy is being hammered? ie the bouy is being hammered every 13 seconds with a bigger wave or altenatively every 3 seconds as you are experiencing with a less powerful wave?

Thanks for all your responses. I've been looking at these things for months and was acting all cool but didn't really have any idea of what it all meant.

The wave period of the graph above indicates a ground swell. Once it starts showing 12 and above you know it is not just a localised wind swell and has come from a long way away (groundswell)


With the swell direction you will notice that it oscillates every 6 hours. As this is from the wavebouy just outside the Rip(Pt Nepean) I suspect it is from tidal influence. Do wave bouys in other locations show this oscillation due to tide?

The swell direction is handy for identifying spots that need a south swell to get in to them. If there is a howling northerly or northwesterly yo can see how it affects this graph from a direction that cannot be groundswell.

Takes a while to understand what this data means but once you get the hang of it is priceless. It is my first point of call for planning my session for the next day and checking it out first thing in the morning.

Another interesting thing regarding period is that longer period swells bend more effectively into protected bays and points. That is why 2 identical size and direction swells can yield very different results at your favourite protected point.

Ya gotta love the internet for surf forecasting!!