Forecast question

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Means nothing zeta , zilch absolutely zilch, always changes every day, day to day.
The only real wave heights you're gonna get are the one you experience in the water surfing;)

If forcast says 5m @ 13 & your nearest swell buoy ( real time ) is the same then alls perfect ? Right

Not necessarily Caml. Depends on what data you're looking at (both forecast and observation). Which location are you referring to? The Margs forecast and the Naturaliste buoy?

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I am looking at https://www.bom.gov.au/products/IDT65014.shtml

I would like to understand the forecast better. I mean its a good tool, it follows a certain set of equations and understanding what is actually shown is well worth it.

Gday zeta...... What exactly don't you get?

As stated in my first post. The wave heights predicted by the forecast, are they effective wave heights? Or what wave heights are we talking?

Zeta, the model forecasts are for deepwater swell trains.

However the live buoy observations - whilst also for deepwater swells - are for Significant wave heights and Maximum wave heights (which we don't plot). Instead, we plot individual swell trains (which is more accurate for surf forecasting).

Nevertheless, there is a reaosnably good correlation between the Cape Sorell buoy and our Cape Sorell forecast: https://www.swellnet.com/reports/australia/tasmania/cape-sorell/forecast

As you can see from the forecast below, the primary swell (which is the only swell train modeled to be in the water) is expected to be somewhere between 7.0m (6am) and 5.5m (6pm). 

This roughly equates with today's Significant wave height observations from Cape Sorell (blue line).

The red line is maximum wave height, which we don't calculate in our forecasts because it's not as useful for surf forecasting.

Where things come unstuck (re: buoy data vs model forecasts) is in the period measurements.

Most buoy software programs don't calculate individual swell periods by default.. they just display Average periods (also known as Zero Crossing), or Significant periods (the average period of the highest 1/3 of all waves), plus Maximum Period. These are different to the swell periods of individual swell trains.

Sometimes they'll match up (ie leading edges with Tmax, and strong solitary swell sources) but as soon as there's a number of swells in the water - for example, when there's a lot of windswell - the Significant period values can become 'contaminated'.

Not sure if that explains things a little better for you?

Cheers, Ben.... There you go, zeta...... I don't use wavewatch3.... I just go by the charts like the one you supplied in your 10.10am post.... I'm just an old school basic sort of forecaster....
You do know how to interpret those charts? as in Hmax etc? That's about all I could help you with....
Oh and using ascat and calculating swell size and arrival.....

Settle

Thanks ben that is very helpful.

Sheepdog wrote:

You do know how to interpret those charts? as in Hmax etc? That's about all I could help you with....

Oh and using ascat and calculating swell size and arrival.....

I am familiar with it from a research point of view as I am working a bit with ocean storms.
That's why I was interested how the wave height is defined in this swell forecast.
I am living only 2 years next to the ocean now so I do not have enough experience to gauge swells like you old dogs.

I have not heard of ascat but I will have a look at that.

Thanks again for all the help.
Cheers