The use of ensemble weather models such as the European Centre for Medium-Range Weather Forecasts (ECMWF) Ensemble Prediction System (EPS) provides a range of probabilistic outcomes which better align with planning and risk management assessments. An automated procedure to bias correct 10 day tropical cyclone forecasts generated by the ECMWF-EPS forecast system has been developed and fully operationalised under the name Ensemble Prediction System Bias Corrector (EPS-BC). This system ensures clients are able to make critical business decisions based on probabilistic forecasts that better represent the natural variability of tropical cyclones across the northwest shelf. Ensemble Prediction System-Bias Corrector (EPS-BC) tropical cyclone track data are now available as an outcome of a Joint Industry Project for Tropical Cyclone Research and companion operationalisation project.
The EPS -BC procedure does the following:
1 Detects tropical cyclones in the ECMWF-EPS
2 Corrects the tropical cyclone properties for systematic bias
3 Inserts a new vortex, constructed to have the bias corrected properties, over the existing vortex in the model fields
4 The new model fields are used as input to further tasks
The EPS-BC uses a multivariate linear regression method to bias correct storm intensity and structure. The system performs bias correction based on data from the previous two seasons.
The fix location of tropical disturbances at a specific time are derived from gridded output from the ECMWF-EPS. The associated values of these disturbances (fixes) notably, maximum wind speeds, central pressure and gale radii may be bias corrected.
The data from EPS-BC has the following attributes:
disturbance_id and cyclone_name: identifiers which group disturbances of the different ensemble members
ensemble_no: ECMWF EPS has 51 ensemble members. Each member can generate a tropical cyclone track
fix_hour: number of hours since base time (model run)
latitude / longitude: position of minimum Mean Sea Level Pressure (MSLP) of the fix. Coodinates are only to 1 decimal place
max_wind_spd_msp / kn: maximum 10 minute mean of the wind speed at a height of 10 metres near the fix, possibly bias corrected. Available in units of metres per second and knots.
central_pres_hpa: minimum pressure in hectopascals near the centre of system, possibly bias corrected.
radius_gf_wind_nmi: radius in nautical miles from the system centre to the outer extent of gales (greater than 34 knots). Although, there are fields for each of the four quadrants (NE, NW, SE, SW), EPS_BC currently only generates one value. Radius possibly bias corrected.
The fix locations are unmodified from the original ECMWF EPS track data.
Using the above values, points (fixes), lines (tracks) and polygons (gale radii) are created and used as the source of the Web Map Service (WMS) and Web Feature Service (WFS).