Sources of Wind Variability at a Single Station in Complex Terrain During Tropical Cyclone Passage

Although Sasebo, Japans, harbor is usually a typhoon haven from tropical cyclone winds, due to terrain-blocking effects, in rare cases damaging winds occur that may be attributed to terrain channeling. Prediction techniques are developed and tested to improve forecast capability of maximum sustained winds and wind gusts that are the basis for tropical cyclone conditions of readiness. Verification observations from a site that was available during 19901998 were found to provide a false sense of security due to its urban location and 13 m anemometer height. Representing the Sasebo terrain effects with a large database of reanalysis winds had limited success unless the top 1000 wind speeds from each cardinal wind direction were used. A parametric wind model that utilized the JTWC wind radii to represent the wind profile shape resulted in better local wind prediction at Sasebo and a small, flat island, but demonstrated the requirement for a wind-reduction factor to represent frictional effects. This parametric wind model, which is multiplied by directionally-dependent acceleration factors to represent Sasebo terrain effects, was most successful for an independent sample of tropical cyclones passing within 200 nautical miles of Sasebo from 20112012 and for selected forecast case studies.