The nowcasting system of the Hong Kong Observatory (HKO), "SWIRLS" (Short-range Warning of Intense Rainstorms in Localized Systems), is capable of forecasting heavy rain that may affect Hong Kong in the coming couple of hours. In addition to supporting the operation of rainstorm warnings and public weather nowcasting services, SWIRLS also provides the Drainage Services Department (DSD) with tailor-made products to enhance its operations and works projects.

The control mechanism of the penstock at Shuen Wan has been optimised through making reference to rainfall nowcast from "SWIRLS". Based on the nowcast, the penstock will be closed automatically at lower tide level when severe weather is about to affect the catchment area, otherwise it will be closed at higher tide level. This design could fulfill the design flood protection standard, optimise seawater ingression in estuary and the nearby wetland area, and protect the wetland environment.

"SWIRLS" also supported the Kai Tak River Improvement Projects of DSD to enhance works efficiency. Using SWIRLS, the contractor would evacuate the workers, machines and materials in the nullah only when heavy rain was imminent over the catchment area, thus works could be arranged more effectively to avoid suspending work whole-day long merely based on rain forecast in weather bulletins. Compared with the work schedule before adopting SWIRLS, the workable hours had increased by around 20%.