Presentation on theme: "PRESENTS: FORECASTING FOR OPERATIONS AND DESIGN February 16 th 2011 – Aberdeen."— Presentation transcript:
PRESENTS: FORECASTING FOR OPERATIONS AND DESIGN February 16 th 2011 – Aberdeen
Marine Weather Forecasts What tools do we use and how do we prepare them?
The meteorological world has moved on a long way.....
Nowadays marine forecasts are prepared using output from NWP – Numerical Weather Prediction Global Atmospheric Model Ensemble Forecasting Spectral wave model
Global Atmospheric Model Solves fundamental equations describing the evolution of the atmosphere
Fundamental to the success of a forecast is an accurate knowledge of the initial state of the atmosphere Short-range forecast - 'first guess’ Observations of actual and derived conditions
The model is run forward in time, typically up to a week ahead During the run, a range of forecast information is produced at set intervals – say 1 or 3 hours e.g. temperature, humidity, pressure, winds
Ensemble Forecasting Model does not fully describe processes in the atmosphere Model resolution insufficient to capture all atmospheric features Initial observations are not available at every point in the atmosphere Observational data cannot be measured precisely
Ensemble Forecasting One method of quantifying the forecast uncertainty is by running the model a number of times Each run has slightly different starting conditions Each run evolves differently with time
Ensemble Forecasting – types of output
Spectral wave model Solves the spectral energy density equation Uses input from the Global Atmospheric Model, e.g. winds, sea and air temperature
Spectral wave model The wave model predicts the energy spectrum at each point at each time step The energy spectrum is processed to produce significant wave height, wave period, wind wave, swell etc
Preparing a Weather Forecast for Marine Operations Start by examining raw forecast data of wind, waves etc Compare starting values with actual observed data Make allowances for model biases Prepare the final forecast figures Disseminate the forecast in required format – e.g. table/graph, operations checklist, 3-D plot etc.
Providers of Marine Weather Forecasts Most oil companies will not have their own in-house forecasting service but will contract out the provision of weather services to a specialist provider. Forecast company – either public or private – will prepare forecasts for a number of clients using their available model data Forecasting companies will use output from one or more global forecast centres e.g. UK Met Office, NCEP, ECMWF Many companies have their own in-house wave model capability
Extreme Wave Height Gather information on wave climate from observations of wave height over as long a period as possible Choose a distribution function to fit the ‘upper tail’ (i.e. the highest waves) of the data Log-normal Weibull Fisher Tippett Extrapolate to a probability of exceedance of 1 in 50 years
Extreme Wave Height (continued) Calculate the highest likely wave corresponding to the maximum value of 50 year significant wave height Combine with other sea-level parameters e.g. storm surge, astronomical tide
Other Extreme Metocean Parameters Wind Current – Tidal, Surge, Residual Air and Sea Temperature Snow and Ice
Change of Extremes in the Future Very difficult to predict how the wave climate will respond in the future Recent changes in North Atlantic wave height have been correlated with the phase of the North Atlantic Oscillation