Custom-made near-shore forecasts

It’s quite challenging to lay cables on the seabed, while also creating accurate wave forecasts for these activities. MeteoGroup allows dredging companies to focus on the former, while they create the latter. It is the job of one of Metagroup’s customers to pull cables from a wind farm all the way to Zeebrugge, with a wave height threshold of 1.5 metres. Reliable wave forecasts are therefore extremely important but are also very complicated to produce. There are several sandbanks off the Belgian coast that interact with the incoming waves in many ways but MeteoGroup has found a way to produce accurate forecasts for this problematic location. These are produced via a newly-developed infrastructure in the cloud that couples atmospheric and wave models. This innovative set-up looks not only at the sea but incorporates atmospheric winds that drive the waves. As a result, we can provide detailed forecasts for your offshore activities.

It is the focus of the Weather Systems Team to improve wave modelling. Hugo Hartmann, senior meteorological researcher, and Sander Hulst, oceanographer, have been working on this with their teammates for some time. Sander says, "I am always aware of the fact that my office is nice and warm when I’m working on all kinds of algorithms to build a reliable forecast. The people who work at sea, and who receive our forecasts, are the ones that have to deal with the outcomes. They get into trouble when wind or wave predictions are wrong. In our improvement reports, we check our algorithms against local observations. This is what we did at Zeebrugge. In the end, it turned out that our new wave model scores very well”.

Forecasts compared to measurements. The wave model scores very well.

Forecasts compared to measurements. The wave model scores very well.

Waves undergo transformation

Waves from different angles, different heights and different wavelengths (periods) influence each other in many ways. "You can clearly observe this at Zeebrugge”, says Sander. “Waves, for example, drift in from the Atlantic Ocean. They pass north of Scotland and turn to the North Sea. When they arrive further south they slide over the Dogger Bank, this is a shallow area and leads to effects such as wave-breaking or change of direction. Further south, approaching the English Channel, wave transformations will also occur. A field of long waves, for example, refracts more than a short-wave field. And then, near Zeebrugge, there are all kinds of sandbanks.” 

Sandbanks not only cause high and long waves to break earlier, they also induce the waves to bend or refract. These effects increase if the sandbanks are closer to the sea surface, such as at low tide. The tide, therefore, clearly influences incoming waves. But in what exact way? These are the physical principles on which Hugo and Sander are working on and which have been introduced in MeteoGroup’s  SWAN wave model. Testing is continuing at more locations and, for one of our dredging customers, these tests have already been completed with positive results for the wave model. "In the past”, says Sander, “at times it could happen that we were half a metre wrong, which can be disastrous for a large project; but now most of the time we are hitting the exact numbers”.

Complex interaction between multiple models

In the deep ocean a coarse model performs well but less so near the shore. This is an environment with many interactions and changes in sea depth and wind speeds. Hugo says, "coarse-scale models are very usable along the edges of a forecasting area. That's good enough. Our model is WAVEWATCHIII, an open-source model into which we import all kinds of data, including wind speed and wind direction. Closer to the shore, we switch to our SWAN model. This model is much more detailed, containing physical principles, tidal information and sandbanks. These high and low water phases are important: Sometimes there is a difference of 8 meters between them”.

The strength of MeteoGroup’s wave forecasts is that models of different types can be coupled. Output of one model becomes input for another. As an illustration, a regional WAVEWATCHIII wave model can be forced by surface winds, computed by a regional WRF domain, and receive its boundary conditions from a global grid. A model run on a high-resolution SWAN grid can take spectral wave data from the regional WAVEWATCHIII, surface winds from the WRF, tidal data from harmonic components, and ice + ocean circulation data from Mercator in order to properly study wave-current interaction.

Harmonic tide over the Southern North Sea

A quick set-up

We do this all in the cloud, which enables us to increase or decrease computer capacity without limits. This means that there is always enough computing space to run our models. In addition, our processes are designed in such a way that we can quickly set up this wave model for any desired location in the world, whatever the size.

A swift and sound forecast may also be crucial for your offshore activities in terms of safety and in creating as many working hours as possible.

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