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How do I read the data on the NOAA buoy pages?
This is a very common question on a lot of surfing forums – the data shown on the NOAA buoy pages tend to be geared towards scientific uses and less so for your average surfer who is trying to understand how conditions at the buoy will impact their local breaks. If you’re thinking about asking this question on a forum or you just want a refresher on how to read buoy data this post is for you.
Finding Your Buoy
Head to the National Data Buoy Center and use the map to find a buoy closest to your location. Be careful about picking buoys that are inside bays, next to a peninsula or in between the shore and islands as those will be unable to detect swell from all directions.
Reading Basic Buoy Information
Click the “View Details” link on the buoy popup to go to the main buoy page. Here is 46255’s buoy page –
Here are NOAA’s descriptions of all these fields. Here is more detail on each field –
WVHT – This is the significant wave height – more details on what this means here.
DPD – Dominant wave period is the period of the highest energy swell in the water.
APD – Average wave period is the average period of all the swells in the water. Note: there are often many swells in the water at the same time. As a surfer you are most often concerned with the highest energy swell but it’s important to note that other swells can have a huge impact on how your local spots are breaking.
MWD – Mean wave direction is, somewhat confusingly, the direction of the swell with the dominant period referenced in the DPD metric. It is not the mean (average) direction of all the swells in the water.
Some buoys only record wind or barometric pressure so make sure that your buoy includes data in all these columns otherwise pick a new buoy.
Multiple Swells?
Let’s really get into the meat of this. There’s never only one swell in the water. Storms and wind events are occurring all over the globe at all times and they are creating waves that end up on your beach. When you see a surfing forecast it’s always a simplified version of what is actually happening in the water. Math-phobic people don’t freak out but I’m about to show a graph…
This is still a simplified view of what is happening in the water but it’s a bit more explanatory than just “6ft @ 12 sec from 270°”. What this shows are all the swells that hit the buoy – how energetic they are and what their period is.
We can see three defined peaks on this graph – 80 @ 16 sec, 85 @ 13 sec (look familiar?), and 30 @ 9 sec (we’ll come back to this swell later so keep it in the back of your mind). These correspond to three different swells in the water. Note that the 85 @ 13 sec swell matches exactly the 13 second DPD we saw above… it’s the same swell! Remember what DPD was – the period of the most energetic (highest peak on our graph) swell.
You can find this graph on your buoy’s page – just search for “Plot of wave energy versus frequency (and period)” – it’ll be a link towards the bottom of the page.
Let’s Talk Secondary
A lot, but not all, wave buoys have another section below this initial one. It will look like this –
Here’s where we can dig in on more detailed swell information. NOAA calls the most energetic swell the “swell” (lol), as in “Swell Height”, “Swell Period”, and “Swell Direction”. They call the most energetic swell with a period less than the “swell” a “wind wave” as in “Wind Wave Height”, “Wind Wave Period”, and “Wind Wave Direction”.
Look again at the graph above – we saw three swells (peaks) on the graph, 80 @ 16 sec, 85 @ 13 sec, and 30 @ 9 sec. Now note that the “Wind Wave Period” is 9.1 sec – that’s the third swell we saw on the graph!
Summary
Hopefully this was a good primer on how to find and read NOAA wave buoy information from their pages. There’s a lot more to talk about here – why does NOAA only show two swells if there are many in the water? What about wind and tide? Most importantly, now that I have this information how do I use it to find better waves!?!?
Check out the other posts on this blog to get the answers to some of those questions and shoot me an email at nickp@lazysurfer.app to suggest more blog topics.
The Lazy Surfer app is a digital surf log that helps you use your surfing data to make better decisions on where and when to surf. Download for free today.
Thanks to @rozetsky for the header image