SWIRLS is the operational rainstorm nowcasting system of Hong Kong Observatory (HKO). Using observations including weather radars, rain gauges, lightning location detection network and meteorological satellites, SWIRLS generates fine-resolution, rapidly updated nowcast of precipitation and convective weather phenomena in the next few hours. Since the operation commenced in 1999, SWIRLS has been evolving continuously, utilizing state-of-the-art nowcasting technologies including artificial intelligence / machine learning (AI/ML) techniques and deep learning nowcast models. Nowcast data services such as real-time nowcast products, automatic alerts and integrated guidance are provided to forecasters, general public and utilities, government departments and special users.

Besides, SWIRLS has participated in international forecasting projects and delivered regional nowcast supports to the meteorological and hydrological services in the Asian region through the Regional Specialized Meteorological Centre (RSMC) for Nowcasting website and various capacity development activities. The community version of SWIRLS, namely Com-SWIRLS, has also been shared with various meteorological services to promote and support research collaboration or operational implementation of nowcasting technologies for improving capabilities in forecast and early warning of high-impact weather.

The major nowcast data products and services of SWIRLS include:

• Quantitative Precipitation Estimates (QPE), based on radar, rain gauges and a blending of both by co-Kriging analyses
• Quantitative Precipitation Forecast (QPF) by variational optical flow and extrapolation of radar echoes up to 6-9 hours
• Nowcast of radar reflectivity and precipitation using several deep learning algorithms including TrajGRU, ConvLSTM-GAN, Earthformer and diffusion probabilistic model, etc
• Nowcast of lightning severity, hail and convective downburst / gust based on radar signatures and model analyses
• Probabilistic Quantitative Precipitation Nowcast (PQPN) based on "SWIRLS Ensemble Rainfall Nowcast" (SERN) with a total of 100 members
• Satellite-based nowcast using Himawari-8/9 data where reflectivity retrieved from the Advanced Himawari Imager data and neural network are blended with radar nowcast to extend the coverage of QPF
• Satellite analysis and nowcasting products based on EUMETSAT NWC SAF/GEO
• Blending of radar-based extrapolation nowcast, and forecast of precipitation or simulated reflectivity from convection permitting NWP models
• Automatic nowcast guidance for supporting rainstorm warning operations: "Automatic Rainstorm Related Objective Warnings" (ARROW), "SWIRLS Integrated Panel" (SIP) and "SWIRLS Time-series And Mapped Probabilities" (STAMP) for integrated display, and "Special Tips on Intense Rainfall" (STIR) for generating text-based rainfall report and forecast
• Location-specific rainfall and lightning nowcast for the public and special users through the ARWF web portal and the MyObservatory mobile app
• Real-time verification system

Year		Title		Author(s)
2024		AI Technology in Nowcasting		Wai-kin WONG
2023		A New Deep Learning Nowcast Model of Radar Imagery using Generative Adversarial Network for Operational Rainfall Nowcasting (presentation)		Ka-hing WONG, Wai-kin WONG, Hiu-wang LAU
2023		ResConvLSTM-GAN: a new deep learning nowcast model for radar and satellite imagery		Hiu-wang LAU, Ka-hing WONG and Wai-kin WONG
2021		Enhancement of the HKO Satellite Derived Radar Reflectivity Algorithm in Recognition of Significant Convection		Wai-soen Chan, Christy Yan-yu Leung and Ping-wah Li
2021		Development of NWC SAF/GEO in Nowcasting Significant Convective Weather in southern China		Wai Kin Wong, Yu Heng He
2020		Development of NWC SAF/GEO in support of severe weather nowcasting in the Hong Kong Observatory		Wai-kin Wong
2019		社群版小渦旋臨近預報系統的協同發展 (in Chinese only)		胡宏俊, 甘栢謙, 石家俊, 吳家豪
2017		Deep Learning for Precipitation Nowcasting: A Benchmark and A New Model		Xingjian Shi, Zhihan Gao, Leonard Lausen, Hao Wang, Dit-Yan Yeung, Wai-kin Wong, Wang-chun Woo
2018		公眾定點閃電臨近預報服務 (in Chinese only)		Wang-chun WOO, Yin-ying IP, Wai-kin WONG, Ngo-hin CHAN
2017		Development of Satellite Reflectivity Retrieval Technique for Tropical Cyclone Rainfall Nowcasting		Wang-chun WOO, Yin-ying IP, Wai-kin WONG, Ngo-hin CHAN
2017		Operational Application of Optical Flow Techniques to Radar-Based Rainfall Nowcasting		W.C. Woo, W.K. Wong
2016		自動以日常用語表達降雨、雷暴及大風實況和降雨預測的系統 (in Chinese only)		胡宏俊, 楊海霖, 梁明德
2015		Blending of Extrapolated Radar Reflectivity with Simulated Reflectivity from NWP for a Seamless Significant Convection Forecast up to 6 Hours		P. Cheung, P.W. Li & W.K. Wong
2015		Convolutional LSTM Network: A Machine Learning Approach for Precipitation Nowcasting		Xingjian SHI, Zhourong CHEN, Hao WANG, Dit-Yan YEUNG, Wai-kin WONG, Wang-chun WOO
2015		Experimental Location Specific Probabilistic Rainfall Nowcast		W.C. Woo, K.M. Lok
2014		Use of NWP for Nowcasting Convective Precipitation: Recent Progress and Challenges		Juanzhen Sun, Ming Xue, James W. Wilson, Isztar Zawadzki, Sue P. Ballard, Jeanette Onvlee-Hooimeyer, Paul Joe, Dale M. Barker, P.W. Li, Brian Golding, Mei Xu & James Pinto
2014		An Overview of Nowcasting Development, Applications, and Services in the Hong Kong Observatory		P.W. Li, W.K. Wong, P. Cheung & H.Y. Yeung
2014		Establishing Integrated Weather, Climate, Water, And Related Environmental Services For Megacities And Large Urban Complexes - Initial Guidance		S. GRIMMOND, G. BEIG, B. BROWN, G. CARMICHAEL, CHEN B., FANG Z., G. FLEMING, A. GARCIA, L. JALKANEN, H. KOOTVAL, LI H., K. LONGO, MU H., PENG L., SHI J., TAN J., TANG X., D. TERBLANCHE, WOO W. & ZHANG J.
2014		Challenges and Advances related to TC Rainfall Forecast		W.C. Woo, Wallace HOGSETT, M. MOHAPATRA, Kazuhiko NAGATA, Peter OTTO, QI Liangbo, VO Van Hoa, XU Yinglong
2014		An Algorithm to Enhance Nowcast of Rainfall Brought by Tropical Cyclones Through Separation of Motions		W.C. Woo, K.K. Li, Michael Bala
2014		應對大雨的特別天氣提示自動編制系統 (in Chinese only)		胡宏俊, 楊海霖, 鄭子路
2014		透過校準數值預報模式提升短期定量降雨預報的表現 (in Chinese only)		李健綱, 陳家樂, 胡宏俊, 鄭子路
2013		Development of a guideline for thunderstorm reporting based on radar and lightning location data		P.W. Li, P.W. Chan
2013		Development of Radar-Satellite Blended QPE Technique and Application to Rainfall Nowcasting		C.W. Ng, H.Y. Yeung
2013		對應熱帶氣旋降雨的臨近預報方法 (in Chinese only)		胡宏俊, 鄭子路, 李健綱
2012		Application of optical-flow technique to significant nowcast for terminal areas in Hong Kong		P. Cheung, H.Y. Yeung
2012		Recent developments and applications of the SWIRLS nowcasting system in Hong Kong		H.Y. Yeung
2011		《小渦旋》臨近預報系統在2010上海世博會的應用 (in Chinese only)		鄭子路, 戴建華, 楊漢賢
2011		Application of Radar-Raingauge Co-Kriging to Improve QPE and Quality Control of Real-time Rainfall Data		H.Y. Yeung, C. Man, S.T. Chan, A. Seed
2010		Development of an Advanced Aviation Nowcasting System by Including Rapidly Updated NWP Model in Support of Air Traffic Management		P.W. Li, W.K. Wong
2010		多尺度光流變法在臨近預報的應用和表現 (in Chinese only)		楊漢賢, 黃偉健, 鄭子路
2009		Development of a Thunderstorm Nowcasting System in Support of Air Traffic Management		P.W. Li
2008		Development of a Lightning Nowcasting System for Hong Kong International Airport		P.W. Li, D.S. Lau
2008		A High-resolution Rapidly-updated Meteorological Data Analysis System for Aviation Applications		C.S. Lau, J.T.K. Wan, M.C.Chu & P.W. Li
2008		Thunderstorm Downburst and Radar-based Nowcasting of Squalls		H.Y. Yeung, S.T. Lai, K.Y. Chan
2007		Lightning Initiation and Intensity Nowcasting Based on Isothermal Radar Reflectivity - A Conceptual Model		Linus H.Y. Yeung, Edwin S.T. Lai, Samson K.S. Chiu
2006		Applications of Nowcasting Products to Real-time Warning of Hazardous Weather in Hong Kong		M.C. Wong, S.T. Lai, P.W. Li
2006		Quantitative Precipitation Nowcast of Tropical Cyclone Rainbands - Case Evaluation in 2006		S.T. Lai, W.K. Wong
2006		From SWIRLS to RAPIDS : Nowcast Applications Development in Hong Kong		M.C. Wong, W.K. Wong, S.T. Lai
2006		Application of Rainstorm Nowcast to Real-time Warning of Landslide Hazards in Hong Kong		Sammy P.Y. Cheung, M.C. Wong, Linus H.Y. Yeung
2006		Nowcasting - the Means for Meeting the Server Weather Challenge		Linus H.Y. Yeung
2005		Use of GPS Signal Delay for Real-time Atmospheric Water Vapour Estimation and Rainfall Nowcast in Hong Kong		P.W. Li, X.Y. Wang, Y.Q. Chen, Edwin S.T. Lai
2005		RAPIDS - A New Rainstorm Nowcasting System in Hong Kong		P.W. Li, W.K. Wong, Edwin S.T. Lai
2004		Applications of Radar-based Nowcasting Techniques for Mesoscale Weather Forecasting in Hong Kong		P.W. Li, Edwin S.T. Lai
2004		Short-range Quantitative Precipitation Forecasting in Hong Kong		P.W. Li, Edwin S.T. Lai
2004		利用廣東省自動氣象站網絡實時資料增強香港暴雨臨近預報的能力 (in Chinese only)		李炳華, 周志堅, 楊漢賢
2003		Merging Nowcasting and NWP in Weather Warning Operations, with Special Reference to Landslides		C.C. Lam
2003		臨近預報在城市地質災害中的應用 (in Chinese only)		李炳華, 林超英
2003		Case Study on the Impact of Radar-derived TREC Winds on Model Forecast of Heavy Rain Associated with Landfalling Tropical Cyclone		C.C. Lam
2003		From Radar Echoes to Landslip Warnings		C.Y. Lam, C.C. Lam
2003		臨近預報在香港『山泥傾瀉警告』中的應用 (in Chinese only)		陳建宇, 李炳華
2002		Strategies of Nowcasting and Forecasting Rainstorms in Hong Kong		Edwin S.T. Lai
2001		Short-range rainfall forecast in Hong Kong		Edwin S.T. Lai, P. Cheung
2001		Radar-based Analyses on the Hailstorm of 9 April 2001		Edwin S.T. Lai, P.W. Li
2001		「小渦旋」- 1999及2000年暴雨驗證及最新發展策略 (in Chinese only)		黎守德, 李炳華
2000		SWIRLS - An Evolving Nowcasting System		P.W. Li, W.K. Wong, K.Y. Chan, Edwin S.T. Lai
2000		Pattern Recognition of Radar Echoes for Short-range Rainfall Forecast		Edwin S.T. Lai, P.W. Li, C.M. Chan, M.C. Chu, W.H. Wong
1999		Preliminary Performance Evaluation of A Rainstorm Nowcasting System		Edwin S.T. Lai, P.W. Li
1999		Short-range Forecast of Heavy Rain based on Radar Echo Analysis		P.W. Li, W.K. Wong, Edwin S.T. Lai
1998		暴雨預報中的溫熵圖及大氣穩定情況分析 (in Chinese only)		陳建宇, 黎守德, 李炳華
1998		從雷達回波的移動趨預報短期的降雨情況 (in Chinese only)		黃偉健, 黎守德, 李炳華
1998		TREC Application in Tropical Cyclone Observation		Edwin S.T. Lai

Year		Event
2023		Trials of deep learning nowcast based on ConvLSTM-GAN commenced.
2021		Com-SWIRLS features modules to process SAFNWC products and enhancements in deep learning nowcast model. Read More
2020		Deep learning precipitation nowcast (TrajGRU) added to Com-SWIRLS. Read More
2020		Nowcast – NWP blending module with enhancements added to Com-SWIRLS. Read More
2019		HKO awarded at the 19th APICTA Awards, and Hong Kong ICT Awards. Read More
2018		RSMC for Nowcasting website (https://rsmc.hko.gov.hk/nowcast) launched with release of the community version of SWIRLS (Com-SWIRLS) nowcasting software codebase. Read More
2018		HKO was designated as a Regional Specialized Meteorological Centre (RSMC) for Nowcasting. Read More
2018		HKO launched for trial operation the regional satellite-based significant convection, super-cool liquid water and ice crystal icing nowcast for aviation applications.
2018		HKO launched a two-hour rainfall and one-hour lightning location-specific nowcasting service on Windows 10 platform. Read More
2018		Lightning nowcast for Ngong Ping 360 began operation.
2017		HKO developed lightning nowcast for Ngong Ping 360 for trial use.
2017		Mr Cheng Tsz-lo, one of the developers of SWIRLS, received the Secretary for the Civil Service's Commendation. Read More
2017		HKO collaborated with Drainage Services Department (DSD), Hong Kong and developed an Early Rainstorm Alarm System for the Kai Tak River Works, winning the "The Association of Consulting Engineers of Hong Kong (ACEHK) Annual Award 2017". Read More or Watch (Chinese only)
2017		The "Big Data Analysis and Decision Support" team, of which STIR being one of the components, won the "Team Award (Internal Service)" under the Civil Service Outstanding Service Award Scheme 2017. Read More
2017		The Hong Kong University of Science and Technology (HKUST) and HKO developed two enhanced deep-learning algorithms on rainfall nowcast, based on Convolutional Gated Recurrent Units (ConvGRU) and Trajectory Gated Recurrent Units (TrajGRU). Read More
2017		HKO launched an one-hour lightning location-specific nowcasting service on HKO's Internet website for the public. Read More or Watch (Chinese only)
2016		The Significant Convection Monitoring and Foreacsting Webpage was put in real-time operation.
2016		An algorithm to simulate radar reflectivity based on Himawari-8 satellite data was developed. Read More
2016		HKO and DSD jointly develop a system, based on SWIRLS, to control the penstock operation in Shuen Wan, Hong Kong, contributing to the improvement of the ecology of the wetland.
2016		HKO hosted the World Meteorological Organization (WMO) WWRP 4th International Symposium on Nowcasting and Very-short-range Forecast 2016 (WSN16) and the WMO WWRP & CAeM Aviation Research Demonstration Project (AvRDP) Training Workshop. Read More
2015		HKO developed blended Radar Reflectivity with Simulated Reflectivity from NWP for Seamless Significant Convection Forecast.
2015		HKO launched the community version of the SWIRLS nowcasting system (Com-SWIRLS). Read More
2015		HKO organised the international workshop on "Rainfall Nowcasting" under the Voluntary Cooperation Programme (VCP) of WMO
2015		HKO and HKUST developed the first deep-learning algorithm on rainfall nowcast. Read More
2014		SIP (SWIRLS Integrated Panel) and ARROW (Automatic Rainstorm Related Objective Warnings) to support rainstorm warning operation in Hong Kong was developed.
2014		The forecast range of SWIRLS was extended from 6 hours to 9 hours based on multi-sensor observations.
2013		The SWIRLS Tropical Cyclone (TC) module was developed. Read More
2013		The application "STIR (Special Tips on Intense Rainfall)" was developed.
2012		HKO launched the Significant Convection Monitoring and Foreacsting Webpage for trial operation on the Aviation Meteorological Information Dissemination System (AMIDS) website.
2012		Location-based rain forecast on MyObservatory launched on a trial basis. Read More
2012		SERN was developed and started trial operation.
2011		HKO started providing lightning nowcast to China Light & Power Hong Kong Limited (CLP). Read More
2011		SWIRLS supported the 2011 Summer Universiade held in Shenzhen, China. Read More
2010		Rainfall nowcast for the Pearl River Delta Region with user-selectable geographical information content launched. Read More
2010		SWIRLS supported the XIX Commonwealth Games in New Delhi, India. Read More
2010		SWIRLS participated in WENS in support of the Shanghai World EXPO. Read More
2010		ATNS went into operational use to provide short-term thunderstorm forecast for the next hour to support Air Traffic Management.
2009		ATLAS won the First Runner-up under the category "Specialised Service" of the 2009 Civil Service Outstanding Service Award. Read More
2009		ATLAS won the Silver Award in the "Best Public Service Application (Small Scale Project) Award" at the Hong Kong Information and Communication Technology (ICT) Awards 2008. Read More
2008		SWIRLS participated in B08FDP in support of the Beijing Olympics Games (B08) Watch (Chinese only)
2007		ATLAS began operation to support lightning warning at the Hong Kong International Airport
2005		RAPIDS began trial run.
2003		"Rainstorm Viewer", a SWIRLS nowcasting tool developed to support the operation of rainstorm warning in Hong Kong
2000		HKO Technical Note No. 100 "SWIRLS - An Evolving Nowcasting System" was published. Read More
1999		SWIRLS became operational in HKO in 1999.
1998		A SWIRLS prototype was put on operational trial.
1997		HKO started the development of the SWIRLS rainstorm nowcasting system.