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Buoy Forecast - Frequently Asked Questions (FAQs)

  • What source data is used to construct the buoy forecasts? Stormsurf buoy forecasts provide you with the most detailed and accurate swell and surf forecasts available. To accomplish this, we use site specific bulletins from the regional runs of the operational NOAA Wavewatch III wavemodel. The advantage of these bulletins is they detail the swell height, period, and direction for each individual swell converging at predefined locations across the globe for up to 6 different swells. The downside is they don't provide as much global coverage as the other major option: GRIB data. But GRIB data suffers in that it only provides information about the dominant 'swell'. If the dominant 'swell' is a windswell, even though smaller but more energetic secondary groundswell is present, the GRIB data will not recognize the groundswell. The paradox is that often the smaller but more energetic groundswell will produce larger waves. From a surfing perspective, period is more a determiner of wave size than swell height. It is for this reason that we felt compelled to use the bulletins, because of their ability to ferret out with a high degree of accuracy high energy swells. The bulletins have excellent coverage for all United States locations, modeling sea state for every NOAA buoy, many Canadian and European buoys and a good collection of virtual buoys outside these locations including Europe, Brazil and the West Pacific.
  • Tell me more about the models and their association with buoy forecasts. Building accurate automated surf forecasts is very dependent upon the ability of the wave model to forecast local sea conditions, specifically those for nearshore buoys that sit within 20 nmiles of the coast. The ability to sort out windswell from groundswell is paramount. Since many ocean enthusiasts have built an understanding of how real-time buoy readings correlate to near shore surf conditions, building forecasts for those buoys to predict future ocean and swell conditions is essential. In general, the bulletin data gets you a forecast for an exact point, accurate to within one tenth of a degree (about 6 nautical miles) and for 6 individual swells hitting simultaneously. In this way the real-time NDBC buoys become a way to verify the accuracy of the wave models. In contrast, the best GRIB regional datasets provide one datapoint for every .25 square degrees (one reading for every 225 square nmiles of ocean surface) and only for the dominant 'swell'. And the global models only have a resolution of 1 by 1.25 degrees (one reading for every 4500 square nmiles). That's still very good for modeling raw sea conditions, but for critical near-shore applications, why not use the best source available? For those locales not covered with regional bulletins, GRIB data is a good (and the only) option. But for everywhere else, regional bulletins are the way to go.
  • Which models does Stormsurf use? As mentioned before, there are currently 5 Wavewatch III wavemodels run in near-parallel, all using the same initial atmospheric state data. The prime one is the global model which provides global forecasts (with less fidelity but more coverage area). There are 3 regional models (West North Atlantic, East North Pacific, and the Alaskan model) which focus on specific regions while providing greater resolution), and two hurricane models which superimpose the fine details of hurricane surface circulation on the regional models providing an even higher operating resolution. Each of these models provides bulletins for specific locations, and with varying degrees of fidelity. These models are the state of the art in predicting conditions on the oceans surface and generally quite accurate. Stormsurf uses bulletin data from the highest fidelity models, the regional and hurricane models, whenever possible to provide the highest level of accuracy and fidelity.
  • Note of Caution: Though the models are state of the art and a tremendous leap forward in wave modeling technology, that does not mean they are infallible. The reality is that there are still physical process in the real world that that are not well understood and constructed in the theoretical world. One has to develop some skill using these models (for several years) to get a good feel for their strengths and weaknesses. The further out the forecast goes, the less accurate it is. But the near-term projections (one to 2 days out) are normally pretty good. Remember, the data you are viewing is raw data. Use it as a rough guile only. Manually computed groundswell forecasts still have the edge in accuracy.
  • How often are the forecasts updated? The models at NOAA are run once ever 6 hours (4 times per day). Stormsurf downloads the data right after it's posted by NOAA, and processes it for presentation on our site. The fresh data is loaded real-time for viewing. The date and time from the source files (model run time) are posted on each page.
  • How is this data prepared for presentation? Each site specific bulletin is parsed using Stormsurf's custom designed proprietary algorithms that determine the two largest swells (of up to 6 that are documented at each site). The 'top two' are selected using the combination of swell height and period that will produce the largest waves.
  • Why only the 'top two' swells? We could have done the top three or four swells, but two seems to be the most that a person would ever notice at one location at a time. Also the pages would get too large to view. As is common in many locations, it is possible to have one ground swell coming from say the south, and another from the north. Or a combination of windswell and groundswell coming from the same direction but with different periods. From a surfing perspective, the groundswell is usually the swell most sought after because of it's concentration of power and energy. The top two seems to account for most normal conditions around the globe.
  • Surf Height from Primary or Secondary Swells: This graph depicts the height of waves that will result when the primary or secondary swell breaks at beaches nearest the buoy. We calculate the surf height using a combination of swell height and period and scale the result using proprietary tables that account for the buoys proximity to land. The surf height estimates are applicable only to those breaks relatively close to the buoy. As you move to beaches further away from the buoy, the accuracy falls off. But in such cases, normally, there are other buoys to select from.
  • Surf Height is not specific to any particular break. It represents the size of the average set wave at a theoretical break that has neither anything to reduce the size of the swell or enhance it. Bathymetry can significantly alter the resulting wave size. Waves can be as much as twice the stated size or down to one half the stated size. Things that can reduce swell size include (but are not limited to) obstructions that prevent a swell from proceeding straight towards the beach, like islands, points or anything that causes the swell to wrap or change direction. Offshore shoals, reefs or sandbars can cause the swell to drag on the bottom and loose energy, reducing size too. Conversely, certain ocean bottom configurations enhance wave size like: deep water trenches that deposit a swell onto a shallow reef or jetties than cause reflections (to name two). In short, use this data in combination with your local knowledge of the breaks near where you surf to determine what location will be best suited for your skills.
  • Primary and Secondary Swell Height and Period: This is the forecast height and period of the Primary and Secondary Swells. Height is in feet and period is in seconds, the same as what is normally reported at the NOAA buoys. Remember, smaller swells with longer periods often result in larger waves than seemingly bigger waves that have short periods.
  • Combined Sea Height (also known as Significant Seas): This is the summation of all the energy expected to be hitting the buoy. It is a rough approximation of the height of the highest 1/3 of all waves that passed under the buoy. Individual swells up to twice this size could occur once every hour. Note that combined Sea Height does not necessarily correlate well to near-shore surf height. Chop and short period windswell can skew the numbers to the high side. That's why we tend to downplay this graph, and provide it as a rough guide only.
  • Surf Height Variability: This graph depicts the variability of surf height caused by the interaction of groundswell and windswell. The more windswell there is, the greater the variability. This data is calculated by first computing the surf height for the primary swell. Next we calculate the surf height for combined seas using the primary swell period as dominant period for the seas (E.g. if swell was 6 ft @ 17 secs and seas were 8 ft, then the input range would be 6-8 ft @ 17 secs). The graph should not be taken too literally, but is provided mainly as a rough guide to help set expectations.

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