High-resolution wind and wave modelling for Weymouth and Portland

olympic sailing at weymouth and portland bay

Using the latest weather forecasting technology to give guidance on the wind and wave conditions for sailors, organisers and safety crews at the Olympic and Paralympic sailing events at Weymouth and Portland during London 2012.

In this article we look at how we used the latest weather forecasting technology to give the best possible guidance on the wind and wave conditions for sailors, organisers and safety crews at the Olympic and Paralympic sailing events at Weymouth and Portland during London 2012.

When it comes to sailing, knowing what the wind and sea are doing is everything - and not just for the sailors; organisers and safety crews need to know what to expect in races when yachts and equipment are being pushed right to their limits.

Forecasting weather for Weymouth and Portland

The venue for the Olympic and Paralympic sailing events at Weymouth and Portland was an ideal spot in many ways, but also posed some complexities for the Met Office team who were forecasting conditions for the races.

Weymouth Bay is sheltered from the predominant westerly and south westerly winds by the Isle of Portland - which is about 4 miles long and 1.5 miles wide. This means the Bay is protected from seas whipped up by these winds, making for better conditions for sailing.

Penny Tranter, from the Met Office, said ahead of the Games: "Local winds in and around Weymouth Bay are complicated because the cliffs around Portland have a big impact on the general west to south-westerly prevailing wind. When winds blow from the west, the seas close to Portland will be sheltered but there will be turbulence further off shore - with eddies and perhaps squalls of wind which could pose a risk."

High-resolution modelling

The Met Office already use enormous amounts of computing power in order to run models that can generate atmospheric weather data every 1.5 km over the whole of the UK.

However, even higher resolution was needed to resolve the complexities of the winds around Portland so a model was used which gave close to 20 times more detail than is usually available.

This ensured the highest detail possible for forecasts for wind and waves in the area during the London 2012 competition.

Wind forecasts

Wind forecasts were generated using an atmospheric model with grid squares at just 333 m by 333 m. The extra horizontal resolution allows the sheltering and coastline effects to be more accurately recreated in the model, providing our forecasters and ultimately the competitors with a detailed forecast that could make all the difference to the competition.

Wave forecasts

The wave forecasts are produced at an even finer resolution, using a model with 250m grid spacing. The wave model represents both the generation of waves by the wind and how those waves will develop as they travel along the coast.

In order to do this correctly the model uses information about waves generated further offshore in the Atlantic or English Channel as one of its inputs, and includes the impact of local tides.

Andy Saulter, from the Met Office's Ocean Forecasting Research department, said ahead of the Games: "The importance of this very high resolution is that it enables us to accurately represent local influences on sea-state due to sheltering by the coastline or changes in depth across the sailing venue.

"With this information we can give competing sailors, organisers and safety crews a much better idea of what conditions they will find at sea before they have even gone down to the water. This will be important for safety as the competitors take their boats right to the limit."

While the output from these specially run models is primarily intended to help Met Office forecasters at the Weymouth and Portland events, it will also be available for the public to see for the duration of the Olympics in the showcase of the high resolution wave model.

The future

With increased computing power in the future, it's possible that the Met Office could, in time, run high-resolution models such as this on a more regular basis not just for UK waters, but across the globe, providing key information to mariners, engineers and others work across the off-shore and marine industry.

Last updated: 18 April 2016

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