Objective calibrated wind speed and crosswind probabilistic forecasts for the Hong Kong International Airport

Wind is a critical weather element in formulating Terminal Aerodrome Forecast (TAF) in tropical cyclone (TC) situations for assessment of crosswind which is known to be the top weather factor causing significant flight delay and cancellation at the Hong Kong International Airport (HKIA). In Hong Kong, the wind and crosswind forecasts and their probability, amongst other weather information, are also contained in the Weather Summary for HKIA which serve as a supplement to TAF to facilitate decision making and cost-benefit analysis by the aviation users. If the forecast uncertainty is high, an alternative scenario is also included in the Weather Summary.

To assist aviation forecasters in the preparation of wind and crosswind forecasts and formulation of an alternative scenario in TC situations, the Hong Kong Observatory (HKO) developed objective wind speed and crosswind probabilistic forecasts for HKIA based on the European Centre for Medium-Range Weather Forecasts (ECMWF) Ensemble Prediction System (EPS) outputs. Post-processing using Model Output Statistics (MOS) technique is applied to the ensemble mean wind speed forecast with a view to calibrating model wind speed forecast by removing the systematic bias. As an enhancement to the aviation weather service, the objective calibrated wind speed and crosswind probabilistic forecasts are also made available to the aviation users up to 36 hours ahead as a trial product.

This paper presents the methodology of the objective calibrated wind forecasts and the verification results based on TC cases in 2009.