THE ENVIRONMENT
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Weather Forecasting, Monitoring and Prediction
To provide the wide range of meteorological services described in the previous section, the observatory maintains a close weather watch round-the-clock. Weather observers at the Royal Observatory Headquarters and Hong Kong International Airport make regular observations on local weather conditions. Additionally, a network of automatic weather stations telemeters real-time weather data to the Central Forecasting Office from 26 locations around the territory, providing comprehensive coverage of regional weather variations.
Wind conditions at the airport and its vicinity are monitored continuously with a network of anemometers. In collaboration with the Guangdong Meteorological Bureau, the observatory also operates an automatic weather station at Huangmao Zhou, an island 40 kilometres south of Lantau Island and strategically located for monitoring tropical cyclones approaching from the south. In mid-1994, an agreement was reached between Hong Kong and Macau for more frequent exchanges of meteorological information. This enhances the weather watch network in the Pearl River estuary region.
Rainfall information is important for water resource management and also because of the susceptibility of slopes to landslips in heavy rain. A dense network of 148 raingauge stations provides information on the spatial distribution and intensity of rainfall in Hong Kong. Sixty-eight of these stations are equipped to provide up-to-the-minute information every five minutes.
--Rain cloud development, movement and intensity within 512 kilometres of Hong Kong are monitored by a weather radar system which also produces objective short-term rainfall estimates at selected locations.
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 a range of about 100 kilometres.
The northwestern New Territories is more susceptible to flooding than other parts of the territory. Water level and rainfall information at Kam Tin is telemetered directly to the observatory's headquarters to allow real-time monitoring of the situation.
Tidal data are collected from nine gauges along the coast for operational warnings of coastal flooding and preparation of annual tide tables. Numerical models are used to predict the likelihood of storm surges in tropical cyclone situations. The public is informed when a significant rise in the sea-level is expected.
Besides surface observations, upper-air conditions are measured with radiosondes carried by balloons launched at the King's Park Meteorological Station. For an overview of weather systems, hourly high-resolution cloud pictures are received from the Japanese Geostationary Meteorological Satellite. The satellite imageries, which cover East Asia and the western Pacific, greatly facilitate the monitoring of weather systems outside the range the radar system.
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For a more effective assessment and monitoring of weather conditions, a software package was developed in 1994 to assimilate available meteorological information on computer workstations. To meet growing computing needs in the Royal Observatory, two UNIX-based computers were installed early in the year. The new computers are used to handle data acquisition, processing, storage and presentation for tropical cyclone forecasting, numerical modelling and statistical analyses. The systems also enable auto-