Interpreting wave data

[Burley_Boy]

I regularly check the wave data to see what conditions are like but I'm not great at determining what I see as opposed to what it's like out there. I don't mind long large waves but short and breaking is a bugger and I have to give myself more time to get to where I'm heading in my small boat.

Can someone run through a good explaination of sea and swell data as well as the wave periods, hmax Hsig and Tpeak and then tie that in to slop and mess etc.
The wave data is on http://www.epa.qld.gov.au/projects/waves/site_param.cgi?siteid=23&paramid=1&var=6

[mackmauler]

start with wind then look at what direction they are, then think about what current is running, for example today when the northerly got up to 15-20 we copped it a bit, the waves were relatively small but enough wind to make em steep.

[Burley_Boy]

Thanks Rob, still interested in interpreting wave data, maybe I should have posted this under saltwater fishing?

[mackmauler]

I thought it was self explanatory? maybe read through the site for a better understanding, assuming there is info there.

for glassy conditions your after very low wind that being your main criteria above all others, current is the X factor good luck with that.

[ba229]

sorry for my lack of correct terminology but this is how I saw it explained on TV at some stage.

Take the wind speed, wind direction and distance the wind will travel over water to figure out how big the swell will be.

The longer (further the distance) the wind travels over water the higher the swell gets. also the strong the wind blows the bigger the swell gets.

So a high wind only needs sort distance.

Light wind, long distance.

But then you need to also take into account the depth of the water as well.

Now I could be completely wrong on all of this but that is how some show I watched recently explained it.

[Fishinmishin]

Pretty much right. As Rob stated, always remember the wind strength AGAINST the water current creates swell and chop. Eg. If winds are 20Knot southerly but current is also 20Knot southerly then you still have a calm day. Beaufort scale is helpfull.

[Heath]

I generally only take notice of the top section.

Hsig - is the average of 33% of the biggest swells.
Hmax - Is the largest wave recorded for the period.

You'll find a glossery of terms HERE (http://www.epa.qld.gov.au/environmental_management/coast_and_oceans/waves_and_storm_tides/wave_monitoring/glossary/)

Wind is the factor that will determin what sort of conditions you will experience outside. It is very possible that you have a 5m swell, but with a light offshore breeze. The conditions on the water would be great. Seas would be flat, however the swell, would see you loose site of land in between sets. On the flip side of the coin. You could have a 0.5m swell and the wind blowing at 30kts. Your conditions would be bumpy & uncomfortable.

Wind against current will again cause uncomfortable conditions. Wind with the current it tends to stay flat.

So basically taking note of the wind will determin what sort of conditions you will get out there. The swell will determin if you actually get out or not!

Another important thing to look at is swell direction.
It is very important for bar crossings. Few weeks back there was a good 2m swell hitting the coast. We went fishing & only had to contend with a knee high shore break.

You say a small boat, so I guess you will be sticking within a few KM of the shore. Current shouldn't worry you too much on the coast. It generally starts to run hard out wider or on the shallow reefs like 9mile.

[Mick]

If you see Joel Parkinson and Mick Fanning driving to the beach with Jet Ski's in tow and about a dozen boards over 8 foot on top of there car - STAY AT HOME!

[Burley_Boy]

Didn't realize that everyone else understood all of this and I was the odd one out duhhh, thanks for having a good shot at it Heath. I'll split the question up a bit...and hopefully all you guys can explain it so that even I get it. ::)

1. As Heath states you can have a 5m swell and relatively flat. So how would that look on the top wave chart?

2. Explain the difference between swell and seas as you read the boating weather.
How would the 5m swell while flat read in the Boating weather report?

3. I note that as the chart today shows the wave height increasing the period of the waves are decreasing thus does that indicate that its getting higher while choppier? I note that you say Heath that you don't even look at the wave periods at all, why not?

4. This is all before we even look at the wind but there I am bright enough to figure lotsa wind=bad, not so mucha wind=good (unless you're sailing) ;D

I head as far as the 36's at the moment Heath in a 16ft fibreglass runabout.

[Cheech]

The way I think of swell and seas, is like on Morton Bay you get a sea (eg 1m between Mud Island and Redcliffe), but there is no swell. In the ocean, you still get that sea (eg 1m), but it sits on top of the swell.

That means if there is no sea, but a 5m swell, the ocean will be just gently rising and falling, with the actual surface flat. But if there is a sea and a swell, you will have a lumpy surface sitting on top of that same rise and fall of the ocean.

If it is a bit windy and lumpy heading out (but safe), I am not normally that concerned about it being a little uncomfortable, provided the wind is not predicted to be against swell for the trip back.

The way I see it, if the wind is low, it is unlikely to create much "sea" on top of the swell, so even though you may have a large rise and fall with the swell, it will not be lumpy and uncomfortable.

Like the others said, if the wind and the sea (swell would be a better term probably) are going in the same direction then they are not fighting each other so calmer, but if they are in opposite directions then the wind creates a wall that the swell hits, so makes it stand up straight, so uncomfortable conditions. A bit like if you are swimming at the beach and standing in the water when a wave comes in. The wave hits you and makes a splash of water straight up. THe wind does a similar thing.

If the waves are say 9 seconds apart, then the rise and fall will be steeper than if they were say 12 seconds apart. 12 seconds will be a calmer ocean all other things being equal.

What I have said here is just what the other guys said. Perhaps just a little differently explained. Hope it helps. If it is wrong, I am sure I will be quickly corrected.

Cheech

[DaneCross]

I'll have a go
1. A 5m swell will see the solid blue line (Hsig) at the 5m mark, there will be the odd bigger wave indicated by the light blue dotted line (Hmax)
2. Swell (I think) is the size of the waves offshore - the rollers. Sea hight is the waves that are blown up by wind on top of the swell thats running (surf thats hitting the coat). As Heath said, swell direction is important. You can have a 3m southerly swell running offshore, but because of the shape of the Gold Coast, it will roll right by and as a boaty, you wont feel it until the 36's or further - thats why the Tweed coast always picks up more swell. An easterly swell is a different story.
3. Wave period is the time between peaks. Shorter period = choppier conditions, brought about by wind and/or wind against tide/current. A ground swell on a calm day will have a greater period between waves.
4. Lotsa wind sux, lotsa wind against current/tide sux even more.
Thats my go,
Dane

[Heath]

Yep,

Cheech has explained well I reckon.

When you said a small boat, I was thinking 4.5m or something :)

The wave data chart doesn't give you any clues as to what the wind is doing. Simply a 5m sell might look something like this image.



The reason I don't look at the bottom is that generally for crossing bars the direction is more important to me, rather than frequency. As the bottom shallows up the waves become more frequent any how.

So at the moment it says a bit under 1.5m, nothing to worry about. But then the wind is blowing from the North at 15kts. So because its a northerly it will be sloppy & a 1.5m swell will make it pretty uncomfortable. What would keep me from going fishing with those factors? The wind simply. If it was blowing W or SW or WNW then I would probly go out.

Truth be known that in a 5m swell you wouldn't be getting out no matter how calm it was.

[Burley_Boy]

Yeah I figured the 5M swell was a "figure of speech" bugger that through the bars.
I'm getting all this methinks what I hadn't thought about is the direction of the swell can be other than just heading towards the shore... but where do I find that data? the local wave recorder at the seaway doesn't give direction and this seems to be the all important variable I've totally overlooked.
Thanks for the patience guys 8)

[mackmauler]

the only one locally that will tell you that is off north stradbroke island.

Wave Direction is one of the headings.

http://www.epa.qld.gov.au/environmental_management/coast_and_oceans/waves_and_storm_tides/wave_monitoring/

[Heath]

Tweed has one as well.

[mackmauler]

Thats not what it says Heath ???