Verification of output from a very high resolution numerical weather prediction model: the 1996 Sydney to Hobart yacht race

Abstract

The University of New South Wales (UNSW) high-resolution numerical weather prediction model (HIRES) has been used to forecast wind direction and speed at a height of 10 m over the Sydney to Hobart race yacht area for the past three years. The model is run routinely, three times daily, at the New South Wales Regional Office of the Australian Bureau of Meteorology in Sydney. One of these model runs is out to seven days ahead and its boundary conditions are provided by the Bureau of Meteorology's global model. For the 1996 Sydney to Hobart yacht race the model was run at 25 km resolution out to five days ahead and was subjected to detailed verification by one of the authors (KLB), who participated in the race aboard the yacht AMP Wild Oats and carried out an observational program during the race. The model winds were verified on a six-hourly basis utilising instrumentation on the yacht. The yacht carried wind sensors, which are situated on top of the yacht's mast at a height of 17.5 m above the water. The authors were interested in both the wind directional trends and the wind speeds forecast by the model. It was found that the model gave overall guidance of good quality but was particularly accurate early in the race when a major wind change known locally as a Southerly Buster occurred just after the start of the race. Later in the race from about the fourth day, the quality of the forecasts decreased in accuracy. An improved version of the model, run at higher resolution (10 km), will be verified again in the next race, in December 1997.