THE ENVIRONMENT
Weather Forecasting, Monitoring and Prediction
To provide the wide range of meteorological services described in the previous section, the Royal Observatory monitors local weather round the clock. Weather observers at the observatory headquarters, Hong Kong International Airport and Cheung Chau keep a continuous watch on local conditions. Additional observations are made by the Royal Navy at Tai O and by the Royal Air Force at Sek Kong.
A network of automatic weather stations, designed and built by the observatory, telemeters weather data to the Central Forecasting Office at the observatory headquarters from Ta Kwu Ling, Lau Fau Shan, Tsing Yi, Sha Tin, Tuen Mun, Wong Chuk Hang, Tai Po Kau, Sai Kung, Tseung Kwan O (Junk Bay) and Waglan Island. These stations help to provide information on weather that may be localised to the densely-populated new towns. In collaboration with the Guangdong Meteorological Bureau, the observatory operates an automatic weather station at Huangmao Zhou, an island 40 kilometres south of Lantau Island, to relay vital information to the observatory when tropical cyclones approach from the south. For the safety of aviation, wind conditions at the airport and its vicinity are monitored continuously by a network of anemometers.
Rainfall information has always been important in Hong Kong because of its relation to water supply and also because of the susceptibility of slopes to landslips in heavy rain. A dense network of about 140 raingauge stations over Hong Kong provides comprehensive coverage on rainfall intensity and distribution. Sixty-seven of these stations are equipped to provide up-to-the-minute information essential for assessing the likelihood of flooding and landslips. Rainfall intensity within 500 kilometres of Hong Kong is monitored with a digital radar system which also produces objective short-term rainfall estimates at selected places. A lightning detection system locates cloud-to-ground lightning within a range of about 130 kilometres and a spherics recorder is used to register thunderstorm activity within about 100 kilometres.
Besides land-based observations, upper-air atmospheric conditions can be measured by radiosondes carried by balloons launched at King's Park Meteorological Station. For an overview of weather systems, hourly high resolution satellite cloud pictures are received in Hong Kong from the Japanese Geostationary Meteorological Satellite. The availability of hourly imageries greatly facilitates the monitoring of weather systems, especially when they are in close range.
For the real-time monitoring of floods in the north-west New Territories, water-level and rainfall information at Kam Tin has been relayed directly to the observatory headquarters since mid-1988. Tide data are collected from nine gauges in the territory for operational warning of sea flooding in Hong Kong. Numerical models are also used to predict the likelihood of storm surges in tropical cyclone situations. Storm surge warnings will be issued if a significant rise in sea level is expected. Wave information for forecasting the sea state of local waters is obtained in real time from a wave recorder which is located at Waglan Island.
Weather prediction requires constant meteorological data exchange with other countries, through telecommunication circuits dedicated to the transmission of meteorological data. To cope with the rapidly increasing volume of data, the low-speed circuit between Hong Kong and Beijing, which was first set up in 1975, was replaced by a 9 600-baud circuit in 1990. Through the new circuit, Hong Kong is able to obtain radar data from Guangzhou and a variety of graphic products from overseas centres.
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