Can the Extreme Rainfall Associated with Typhoon Morakot (2009) Happen in Hong Kong?

Abstract

ABSTRACT Typhoon Morakot hit Taiwan in August 2009 and brought torrential rain and high death toll to the region. The registered maximum cumulative rainfall depth approached the world record of the greatest point rainfall. In this paper, the risk of experiencing rain episodes of similar severity in Hong Kong was assessed using the Advanced Research WRF (Weather Research and Forecast) model to simulate a direct hit of Typhoon Morakot to the city. A number of numerical experiments were conducted by transplanting the vortex of Morakot and the associated environmental conditions to the South China Sea to study the amount of rainfall that could fall in Hong Kong. The results revealed that the difference in the topography between Taiwan and Hong Kong alone accounted for more than 60% of the total rainfall registered in Taiwan. The enormous land mass of China to the north of Hong Kong would also weaken Morakot rapidly upon its landfall over the south China coast, causing a shift in its track and redistribution of rainfall, and a further reduction of the rainfall amount that Hong Kong would receive. Despite that, some experiments suggested that Hong Kong could receive nearly 800 mm of rainfall in 24 hours, a figure that would break the historical record of 697.1 mm set in 1889 in Hong Kong.