Chapter 16: Meteorological Services

The Hong Kong Observatory was established in 1883, mainly to provide scientific information for the safe navigation of ships. Since then, it has evolved in line with community needs providing services in and studies on weather forecasting, hydrometeorology, climatology, physical oceanography, aviation and marine meteorology, and radiation monitoring and assessment. The Observatory also operates the official time standard for Hong Kong, provides basic astronomical information and maintains a seismological monitoring network.

The Central Forecasting Office at the Observatory's headquarters is responsible for issuing weather forecasts and warnings of hazardous weather. Marine weather forecasts cover the South China Sea. Forecasts and advice are also provided to civil aviation, business and industrial communities, port and container terminal operators.

Whenever Hong Kong is threatened by tropical cyclones, frequent warnings are widely disseminated together with advice on the precautions to take. A colour-coded rainstorm warning system warns people of heavy rain that may cause serious road flooding and traffic disruption. The Observatory also issues warnings on thunderstorms, landslips, fire danger, strong monsoon, cold and very hot weather, and frost. An advisory service on the ultraviolet (UV) index is also provided.

Weather programmes for the public are presented regularly on television by the Observatory's meteorologists. During adverse weather, live interviews and briefings are given over the radio and television. Weather information is disseminated to commercial communications services, making it available on various electronic media.

The Dial-a-Weather service operated by the Observatory provides recorded weather messages to the public. In 2001, over 20 million calls were handled.

The Telephone Information Enquiry System is an interactive system through which the public can obtain a variety of meteorological, geophysical and time information by phone or by fax. In 2001, the system handled around one million enquiries.

The Observatory maintains an informative Internet web site which is continually enhanced with new features. To facilitate accessibility for the visually impaired, an audio version was launched in 2001 to provide weather information in audio format. To enable mobile phone users to obtain the latest forecasts, warnings and information on current weather, a WAP (Wireless Application Protocol) version of the web site was also launched in 2001. The total number of visits to the web site(http://www.hko.gov.hk) exceeded 100 million, or about 300 000 per day on average.

The Observatory exchanges weather observations with the rest of the world through the Global Telecommunications System operated under the auspices of the World Meteorological Organisation. About 16 000 weather reports are received each day through its telecommunication lines with meteorological centres in Beijing and Tokyo.

Hourly pictures of cloud and water vapour distribution are received from both the Japanese Geostationary Meteorological Satellite and the Chinese Fengyun-2 Satellite for monitoring tropical cyclones, severe storms and frontal systems over most parts of Asia and the western Pacific.

The Observatory's Doppler weather radar at Tai Mo Shan provides high-resolution rainfall and wind data for monitoring severe weather within some 500 kilometres of Hong Kong.

Weather observers and 67 automatic weather stations in Hong Kong provide comprehensive and real-time coverage of regional weather variations, while observations from Voluntary Observing Ships provide valuable information on weather at sea.

Rainfall information is important because of the occurrence of flood and landslips during heavy rain. A network of 111 automatic reporting raingauges provides real-time information on rain distribution and intensity for the operation of rainstorm and landslip warnings. An operational nowcasting system combines radar and raingauge analysis to forecast rainfall in the next two hours.

The Observatory runs high-resolution numerical weather prediction models using a high-speed computer to enhance the capability of rainstorm forecasting. Using guidance from numerical products from both global and limited area models, forecasters can now issue weather forecasts several days ahead with reasonable confidence.

In March, the Observatory issued an experimental forecast on the total rainfall and the number of tropical cyclone affecting Hong Kong in the year, as part of a pilot study on long range forecasting.

The Observatory operates tide gauges to monitor raised sea levels and coastal flooding caused by tropical cyclones. To probe the upper atmosphere, radiosondes carried by balloons are launched three times a day at King's Park to measure weather conditions aloft.

The Observatory exchanges weather radar images with the Guangdong Meteorological Bureau and operates jointly with the bureau four solar-powered automatic weather stations at islands in the Pearl River Estuary area to provide better timing of the approach of hazardous weather such as fronts, squall lines and tropical cyclones.

The Observatory operates the Airport Meteorological Office (AMO) at the Hong Kong International Airport to provide weather services for civil aviation. The AMO is responsible for the provision of weather services for a designated airspace over the northern part of the South China Sea. It keeps a close watch on the weather and issues warnings on hazardous weather over this airspace. It operates a web-based automatic information service to provide aviation users with flight documents, latest aerodrome forecasts and warnings, and other weather information. Weather briefings are provided to pilots and other users as needed.

The terminal Doppler weather radar at Tai Lam Chung maintains close surveillance of conditions around the approaches to the airport in order to detect windshear in rainy conditions.

The Observatory operates an environmental radiation monitoring programme to monitor radiation levels in Hong Kong. The programme entails the measurement of samples of air, water, soil and food collected regularly at several sites. A network of stations monitors the ambient gamma dose rate continuously and warns of any deviation from normal levels. Data are disseminated to the media daily, and published in monthly bulletins as well as annual reports. In an emergency, the Observatory will intensify radiation monitoring and assess the radiological and meteorological information collected to estimate the transport, dispersion and deposition of any radioactivity over Hong Kong. The Observatory will also provide technical advice to the Government on counter-measures. An aerial monitoring system will be flown on a helicopter to monitor radiation levels on the ground and at various altitudes over Hong Kong.

Designed for automatically collecting and processing radiation data and messages, the emergency radiation data management system was put to test in a government-wide nuclear emergency exercise conducted in February. It facilitated efficient sharing of vital data and information amongst key departments in the Government's emergency response organisation and contributed significantly to the timely implementation of counter-measures during the exercise.

Climatological information has applications in activities ranging from recreation through engineering design and environmental impact analysis to litigation. To meet the demand for such information, the Observatory operates a climatological information service on a cost-recovery basis. The data available include surface and upper-air observations from Hong Kong and neighbouring countries, marine weather observations from Voluntary Observing Ships and tidal observations.

The Observatory produces an annual tide table for Hong Kong. It also provides assessments of the probabilities of occurrence of extreme storm surges and advice on oceanographic matters to other government departments and the engineering community.

To monitor earthquake activities in the vicinity of Hong Kong, the Observatory operates a network of eight short-period seismograph stations. Long-period seismographs at the Observatory's headquarters detect tremors world-wide and information on significant tremors is made public through the media. In addition, three strong motion accelerographs were installed on different geological sites. On average, Hong Kong experiences two to three minor earth tremors every year.

The Hong Kong Time Standard is provided by a caesium beam atomic clock. Accuracy within fractions of a microsecond a day is maintained. A six-pip time signal is sent to Radio Television Hong Kong for broadcast at quarter-hour intervals. The time checking service is also available to the public through the Observatory's Telephone Information Enquiry System. In addition, a time-server accessible through the Internet is available for the public to synchronise the clock on their personal computers. The time-server performed over 120 million checks in 2001, or about 350 000 checks per day.