Weather forecasts are needed for short-term planning of offshore activities, for example vessel transfers and lifts. The closer the forecast is to the activity, the more reliable it gets. Metocean data recordings are used to provide real time data to support offshore activity, to verify forecast tools and to resolve disputes regarding weather downtime.
Key metocean parameters that impact installation and commissioning activities are wind speed, wave height and current.
What it costs
About £70,000 for a 450 MW floating offshore wind farm.
Who supplies them
Anemometers and lidars: AXYS Technologies, EOLOS, Gill Instruments, Leosphere, ZX Lidars and Wood Group.
Current and wave buoys: AXYS Technologies, OSIL Partrac and RS Aqua.
Weather forecast services: Fugro, Met Office, Kjeller Vindteknikk, MetoGroup, StormGeo and Vento Maritime.
In addition, the vessel contractor generally provides wind measurements (for example via anemometer mounted on crane boom or lidar).
Weather plays a crucial role in offshore installation and commissioning activities as it has an influence on the sequence and duration of planned activities and may lead to delays, which result in elevated costs. This is because all offshore activities have weather limits within which they can be conducted safely and exceeding these would be unsafe.
Weather forecasts are generated through global meteorological models that may be improved in their accuracy with finer resolution local models and feedback of actual data.
The weather forecast supplier usually offers several options, both in the number of forecasts per day as well as forecasts for the different locations. For example, forecasts for the base harbour and the offshore site or a complete forecast for base harbour, the offshore site and transit route.
Forecasts usually include several different meteorological parameters (for example wind speeds at different heights, wave and swell height and wave period) as well as general weather information (for example visibility, lightning risk, fog, water and air temperature and rain). The forecasts are used to plan shipping, lifting and other installation activities based on when weather windows are available.
Wind parameters are usually measured with a lidar (on a fixed or floating meteorological station) or an anemometer (rotary or ultrasonic) on a fixed metrological station with tall mast. The advantage of the lidar is that wind speed and direction at different heights can be determined.
Ocean parameters can be measured with a wave buoy or current meter although there is a trend towards complete systems that combine both wave and current measurements.