Implications of Typhoon York on the design wind speeds in Hong Kong

Abstract There are significant differences between the design wind speeds recommended by the Hong Kong Code-1983 (Code of Practice on Wind Effects, Hong Kong, Building Development Department, Hong Kong, 1983) and those predicted by the Monte-Carlo simulation model (Design wind speeds in tropical cyclone-prone regions, Ph.D. Thesis, The University of Western Ontario, London, Ontario, 1985). The differences are due to the difficulty in determining the ratio of surface to upper-level wind speeds in typhoons, particularly for regions of complex topography. Typhoon York, which struck the Hong Kong area in September 1999 and was the strongest typhoon in that region since 1983, provides an opportunity to revisit the Hong Kong code design wind speeds and the wind field simulation models (e.g., Design wind speeds in tropical cyclone-prone regions, Ph.D. Thesis, The University of Western Ontario, London, Ontario, 1985). In this paper, Boundary Layer Wind Tunnel Laboratory's typhoon model is used to recreate Typhoon York and an alternative approach is developed to model the hurricane boundary layer. The wind speeds and wind direction recorded at different anemometer locations around the Hong Kong area during the passage of Typhoon York are compared with the simulated time histories at these stations. The results show good agreement between the observed and the simulated wind speeds which support lower ratios of upper-level to surface wind speeds than are used in the current Hong Kong code.