I.8.3 Weather forecasting and metocean data

Function

Weather forecasts are needed for short-term planning of offshore activities (for example vessel transfers and lifts) and 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 £600,000 for a 1 GW wind farm.

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.

Metocean measurement devices can be rented or purchased.

Who supplies them

Anemometers and lidars: AXYS Technologies, EOLOS, Gill Instruments, Leosphere, ZX Lidars and Wood Group.

Current and wave buoys: AXYS Technologies, OSIL Sonardyne, Partrac and RS Aqua.

Weather forecast services: Clyde Space Ltd, Fugro, Met Office, Kjeller Vindteknikk, MetoGroup, StormGeo and Vento Maritime.

Aerial surveys: HiDef Surveying.

In addition, the vessel contractor generally provides wind measurements (for example via anemometer mounted on crane boom or lidar).

Key facts

Weather plays a crucial role in offshore installation and commissioning activities as it has an influence on the sequence and duration of planned activities (which need to be conducted safely that is all offshore activities have weather limits, exceeding these would be unsafe) and may lead to delays, which result in elevated costs. 

Weather forecasts are generated through global meteorological models that may be improved in their accuracy with finer resolution local models. Forecasts usually include several different meteorological parameters such as wind speeds at different heights, wave and swell height and 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 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.