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How to create surf forecasts and reports online
Pipeline surf report
In this article I'm going to give a very brief outline of how modern surf reports and forecasts are created and a quick look at some of the technologies used
To give an example of the results that can be achieved through the methods discussed I will be refering to yo Surfer a global surf forecast and community site. I'm also using this technology closer to home for my Cornwall surf report.
A quick look at the Pipeline Surf Report page would be a good place to start.
The report page has several features:
- Wave height
- Swell period
- Swell direction
- Wind direction
- Wind speed
- Tide times
- Sea temperature
Where does the data come from
Nearly all the data used in the surf forecasts comes from the NOAA Wavewatch III model. This processes current observations and extrpolates them 7 days into the future with a fairly high degree of accuracy.The model includes the following variables:
- DIRPW - surface Primary wave direction [deg]
- DIRSW - surface Secondary wave direction [deg]
- HTSGW - surface Sig height of wind waves and swell [m]
- PERPW - surface Primary wave mean period [s]
- PERSW- surface Secondary wave mean period [s]
- WDIR - surface Wind direction [deg]
- WIND - surface Wind speed [m/s]
- WVDIR - surface Direction of wind waves [deg]
- WVPER - surface Mean period of wind waves [s]
Not only are these variables available at 3 hourly intervals for the next 7 days, they are available for practically every degree latitiude / longitudeof the entire planets oceans. The file with this info is known as a grib file (gridded data) which is available from the NOAA website as a download. It is also updated every 6 hours.
So what and how do you use this staggering array of data?
How to use the NOAA data
The grib format is a form of binary compression and as such requires a special tool to 'degrib' it. One such tool is degrib which will output it to a variety of formats, possibly the most useful of which is CSV which can then be loaded straight into a database.This pretty much takes care of the forecasting side of things and the textual side of things but what about those pretty charts?!
How to create the swell charts and graphics
To create the forecast charts took me absolutely ages to figure out so I'm not going to give too much away here!!It basically requires some server side software to interpret the gridded data from theNOAA grib files and output them as a graphic.
The tide forecasts rely on a bit of server side softwarecalled XTide. XTide works by using what it calls harmonics files - these allow the program to create tide predictions based on past observations. It is worth noting that the accuracy of the predictions varies according to the age of the harmonics file and some of these are now getting somewhat out of date.
XTide is nice because it produces both a textual and graphical representation of the tide times
What other factors are used in the forecasts
The NOAA WWIII model is fairly accurate at what it doesand it would be tempting to use the raw dat. Unfortunately it isn't quite that simple and there are a whole bunch of other factors that need taking into account.
The surf forecasts on Yo Surfer are based on an algorithm that is a little like the Colonel's secret but it does take many factors into account. These include the relative swell direction, swell period, wrapping effect of the swell and the overall exposure of the spot.
At the end of the day the predictions are fairly acurate for many spots a lot of the time, however there are always going to be spots and conditions that are difficult to predict. These include local wind swell effects and spots with odd bathymetry (the topography of the ocean floor)