An Operational Statistical Scheme for Tropical Cyclone Induced Wind Gust Forecast

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Qinglan Li, Pengcheng Xu, Chunyan Cao, Lijie Zhang, Guangxin Li, Xingbao Wang, Cheng Li, Hongping Lan

Tuesday 30 june 2015

12:54 - 12:57h at North America (level 0)

Themes: (T) Extreme events, natural variability and climate change, (ST) Hydrological extremes: floods and droughts, Poster pitches

Parallel session: Poster pitches: 5I. Extreme - Flood Drought

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Tropical cyclones (TCs) are among the most destructive natural phenomena. The wind gust and heavy precipitation induced by offshore TCs are the two most important impacts of landfalling TCs. Due to the limitation of real time observations, forecasts of wind gust induced by offshore TCs are mostly based on forecasters' experiences. This study tries to supply a quantitative forecast method through an investigation of the relationship between the wind gusts observed at the automatic weather stations (AWSs) and TCs’ main characteristics, i.e., TC intensity, TC distance to the station, TC’s azimuth relative to the station. Historical TCs data from 1968 to 2013 with the distance of 700KM to several AWSs in South China are analyzed. The wind gust data for the same period at six coastal AWSs: Yantian Port, Mawan Port, Shekou Terminal in Shenzhen and Hong Kong Observatory, Cheung Chau Island, Waglan Island in Hong Kong, are used to build the statistical relationship between the wind gusts and TCs’ main characteristics. The relationship between the wind gust and TCs’ main characteristics are clearly illustrated with novel figures in which the local wind observations are projected onto the TC’s track. The probability of gale occurrence (wind gust >= 17m/s) at these six stations are also computed and synthesized in figures. These figures can be used as references to forecast the gusts at the AWS induced by offshore TCs. Analyses results show that the wind induced by TCs is intermittent. The wind induced by offshore TCs is strongly affected by the surrounding circumstances of the stations. In North Hemisphere, the wind gust observed by AWS is weaker if the land is at its Southeast. By contrast the wind gust observed by AWS is stronger if its Southeast is open water. Usually, Hong Kong stations, which are more open to the South China Sea, suffer more from wind gusts induced by TCs than stations in Shenzhen. The most dangerous area is Northeast quadrant of TCs. At this quadrant, Typhoons which is at the distance of more than 400kms might incur gale at coastal stations in South China.