Weather forecasting: and you thought it was all about seaweed

Paul Boughton

Fisher and so-on and so-forth.Any mariner who has sailed in British waters is almost certain to have encountered the...  

But the services provided by this agency to the maritime sector run far deeper than that, are available worldwide and are extensively used by the offshore oil and gas industry, typically for routing purposes, during critical in-field operations and for ‘routine’ activities such as survey. The Met Office’s services are extensively utilised by the wider maritime hydrographic survey too – on the high seas and during mundane local port-related activities.
In many respects, the advent of North Sea oil and gas opened a new door for the Met Office back in the 1960s, since when the agency has developed a suite of bespoke services for the industry, gradually taking it international over the decades as demand for such services grew.
The Met Office services, even at their most traditional – measuring and forecasting weather conditions and systems – are of huge importance to the commercial maritime sector.
“There will be days when conditions are ideal in terms of wind and sea state to do a job but you find you can’t do it because of thick fog,” says Aberdeen-based Peter Buchanan, operational services development manager.
“It’s a sad fact of life that when you have very little wind in the North Sea and very little sea, these tend to be the times of fog risk. Sometimes operators forget to take that into account. They’ll look at a forecast and say, oh, not much wind, not much sea, we can do the job. And then find they can’t because the visibility is impeding things. Perhaps where there is the need for a proper line-of-sight reference point or there may be safety issues that dictate that they can’t operate in poor visibility, or that visibility is physically stopping technical staff coming out to do the job because helicopters cannot fly.”
But its not just about atmosphere, the Met Office is deeply immersed in the oceans too.
“We have to develop a separate modelling environment for metocean because the oceans behave in a different way to the atmosphere. They’re both complex fluid dynamics problems, but they operate differently.
“We have to understand the oceans in terms of wave motion, also in terms of currents. That science has to be applied in a slightly separate modelling environment. But, clearly the atmosphere provides winds and winds drive the waves so, at some point atmospheric and wave models have to interact, so we have to couple them.
Buchanan says a lot of the Met Office’s R&D effort has been directed at ocean, wave and atmospheric modelling; to make the models more consistently accurate and enable them to forecast more aspects and extend high levels of accuracy into the future. But he stresses that it is important to recognise that weather forecasts are not perfect. However the times when forecast and real conditions don’t match up are decreasing. This has in turn spurred research into that uncertainty in a bid to measure it in an objective way.
“In the past we’ve done weather forecasts and the client has said we’ve got to make an important decision. We’ve got to hire three vessels at £300 000 a day, can we rely on this forecast.
“We’ve now tackled that and developed what we call ensemble forecasting – where we do lots of forecasts instead of one. This then brings risk factoring into play. It recognises that forecasts are not perfect, and for a variety of reasons, the most basic being that every forecast model requires initial conditions to base its forecast on. And, while we make every effort to ensure those initial conditions accurately reflect the then current state of the atmosphere, there is a ‘ball of uncertainty’ surrounding each observation of the atmosphere.”
But its not just today’s weather and metocean conditions, or those anticipated several days ahead that are used to inform models and clients, there is also the vast Met Office archive – a process known as ‘hind-casting’. It too can be and is used for planning purposes.
Buchanan: “If you’re planning an operation in the North Sea at a certain time of year that requires operating limits of x sea height or y wind speed and direction, we can look at the archive and that should inform how often such and such an event occurs and what the likelihood of getting it is.
“That can impact when someone plans to do a job and that in turn influences the estimated costs of the job too. The archive therefore can be used even for costing services when the client is getting a tender together and also for building in the risk factor.”
Ocean route planning is clearly critical, but if one is involved in say a significant seismic survey, maybe a 60-day mission around the Falklands, what then can the Met Office bring to the survey company's table?
“We can start helping at the planning stage … find out what time of year, what the critical operating limits are for the job and then supply the client with data.” says Buchanan. “Before they even start the job they can see how often they're likely to work, what the typical weather is at that time of year and plan accordingly around that. In the operating phase, we can provide a variety of products. So, for example, provide a week ahead, site-specific forecast. If we know the route, we can provide forecasts at points along that route and for each point provide quite a high resolution forecast, say every three hours out to a week ahead for factors like surface wind speed and direction, wind gusts; also sea height, main swell direction and period.
“Wave period will affect how the vessel moves. If vessel movement is critical to a particular survey there are other sophisticated tools that we can provide, such as an actual vessel response forecast where we deliver what we call spectral data from the wave model".
Of course, weather satellites play a very important role in building global and local weather and metocean profiles. They are becoming increasingly sophisticated and can measure a whole range of parameters from space, including sea temperature, wave height and wind speed and direction at the surface of the sea. l

Recent Issues