An Algorithm to Enhance Nowcast of Rainfall Brought by Tropical Cyclones through Separation of Motions

The Hong Kong Observatory operates an in-house developed nowcasting system, namely “Short-range Warning of Intense Rainstorms in Localized Systems (SWIRLS)”, to support the operation of rainstorm and severe weather warnings as well as to provide rainfall nowcast services for the public and for special users in Hong Kong. Aiming to enhancing its performance in nowcast of rainfall brought by tropical cyclones, a new radar echo tracking scheme that separates the motion of the spiraling rain bands from the overall movement of tropical cyclone has been developed. Back-testing with historical cases in the past ten years reveals that the new scheme is more capable of preserving tropical cyclone rain band structures and can enhance forecast skills.