Reduced gust factor for extreme tropical cyclone winds over ocean

Abstract

Information of gust factor (ratio between a short-duration peak gust wind speed to a long-duration mean) for extreme winds is of paramount importance for structural design and risk assessment. However, in-situ measurements were generally made for weak winds, and observations of gust factors for 10-min mean wind speeds over 50 ​m/s have been rarely reported, especially over the ocean. On August 23, 2017, the center of Super Typhoon Hato passed directly over an offshore island named Huangmaozhou in the South China Sea. An anemometer at the weather station on the island recorded a maximum 3-s gust wind speed of 84.2 ​m/s, 1-min mean wind speed of 74.0 ​m/s, and 10-min mean wind speed of 70.9 ​m/s during the typhoon. Based on the wind records from the anemometer, the variation of the gust factor with wind speed is examined in this paper. It was observed that for 1-min mean wind speeds between 10 and 70 ​m/s, the gust factor initially increased with increasing wind speed and plateaued at wind speed between 30 and 50 ​m/s before exhibiting a decreasing trend until 70 ​m/s. The reduced gust factor at very high wind speeds over ocean was observed and reported for the first time, which may have strong implications in tropical cyclone studies and engineering applications.