I came across this article on surfline, which basically is an advertisement for surfline premium combined with an "explanation" about why it's ok to call computer generated models "buoys". The main point is nonsense, but is there a way for the average joe to access the "behind the scenes" information that the NDBC doesn't readily post?
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Apr 18, 2013, 06:25 PM #1Member
- Join Date
- May 2007
Forecasting Q regarding Surfline claims
Apr 18, 2013, 07:10 PM #2
- Join Date
- Jan 2009
- milton delaware
In the example they use, there is only 2.5 feet of 15 second swell, 3.2 feet of 8 second swell going in another direction, and some other trace swells. There is no "pure" 4.6 foot 14 second swell like you might expect to see based on the buoy report. So you show up at the beach looking for something like the 4.6 feet at 14 seconds, when there is only 2.5 feet of swell that is actually headed towards the coast, and the rest of the 4.6 feet of swells are headed in various other directions.
I dont know how to get the hourly NDBC data from different stations broken down in to the individual swells.
Apr 18, 2013, 07:46 PM #3Senior Member
- Join Date
- Sep 2012
- VA Beach
post it. The link is an example from the Cape Charles bouy, but there is similar data available for any other bouy on the NBDC site. As noted though, the surfline "bouys" help by visualizing the data in a more directly applicable format.
Last edited by jasorod; Apr 18, 2013 at 07:51 PM.
Apr 18, 2013, 08:02 PM #4Senior Member
- Join Date
- Apr 2012
yeah - kinda need a little coding to make much of that jumble
Apr 19, 2013, 11:45 AM #5
She Blinded me with Science!
I think we all come up with our own most pridictable interpretation of what we read and then compare the results to the actuality of what see when we get to our favorite spot.
May 26, 2013, 01:37 PM #6
- Join Date
- May 2006
- Lewes, DE
Didn't read the read the article, but like Mitchell said, the combined wave height can be broken into swell components using statistical methods.
Let me dive a little deeper. At any moment in time, at a particular location, there are waves coming from all directions at different frequencies (wave periods). The significant wave height expressed on buoys is defined as the top 1/3 of all waves during a given time period. That means 2/3 of the waves will be smaller, and 1/3 of the waves will be bigger.
The significant wave height can be very useful in wave forecasting, however its primary use has been defined for mariners in the open ocean as it doesn't discern which direction the waves are coming from or at which frequencies.
Lets say your beach faces East, and you have 2 primary swell components. Swell 1 is coming from the NE with a wave height of 4 ft @ 14 seconds. Swell 2 is a local wind swell of 5 ft @ 6 seconds coming from the SE. The significant wave height may be around 6 ft, but if you didn't look any further past the significant wave height, then you wouldn't notice Swell 1, which can produce bigger and more powerful waves then the local wind swell. Even more confusing, when interpreting the significant wave height, is when you have a strong offshore wind producing waves moving away from the coast.
On Swellinfo, on the "station data" map, you can hover over the buoy location, and it will give significant wave height, and swell height if available. You can get the entire spectrum of wave energy from the ndbc real time data link, which can be broken into further swell components. Here is the page for buoy 44009:
http://www.ndbc.noaa.gov/data/realtime2/44009.data_spec. To explain this page, it is essentially wave energy for each frequency.
The Swellinfo Wave forecasts are based off the top 2 primary swell components taken from our wave model. You will find these 2 swell components on the forecast page, text detail and when you hover over the timeline. In order to measure how a forecast is, its good to look at the buoys, but look at both the significant wave height as well as the primary swell. The trickiest forecasts, are when 2 swell are combining together to form a bigger overall swell. This is the exception, more then the rule, but that is often when you will see Swellinfo undercall (as of now).
One other note, buoy locations can be close to the coast or maybe 10-20+ miles away. So, wave height measurements 20 miles off the coast, are obviously going to be different as you get closer to a location. Keep this in mind when you are comparing forecasts to buoys, especially the local steep windswells that are moving parallel to the coast, where wave heights are going to be much bigger offshore.
Hope that helps,