ENG-1998 — Page 490

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THE ENVIRONMENT

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Weather Monitoring and Forecasting

The Hong Kong Observatory maintains a close meteorological watch round-the- clock. It exchanges weather observations with the rest of the world through the Global Telecommunications System operated under the auspices of the World Meteorological Organisation. Through its telecommunication lines with meteorological centres in Beijing, Tokyo and Bangkok, about 20 000 weather reports are received each day.

Hourly cloud pictures received from the Geostationary Meteorological Satellite of the Japan Meteorological Agency give general indications of tropical cyclones, severe storms and frontal systems approaching the South China coast. The Observatory's weather radar system at Tate's Cairn detects rain within about 500 km of Hong Kong and gives estimates of rain intensity and movement. Information on thunderstorms as detected by a lightning location system is also available to forecasters. A new weather radar system will be set up at Tai Mo Shan in 1999.

Weather observers and automatic weather stations at about 40 locations in Hong Kong provide comprehensive and real-time coverage of regional weather variations. Observations from Voluntary Observing Ships provide valuable information on weather at sea.

Rainfall information is important because of Hong Kong's vulnerability to floods and susceptibility to landslips during heavy rain. A dense network of about 70 automatic reporting rain-gauges provides real-time information on rain distribution and intensity over Hong Kong for the operation of rainstorm and landslip warnings.

After a critical review of warnings related to heavy rain, a revised rainstorm warning system was put into operation in March 1998. An amber rainstorm signal was introduced for public dissemination in addition to the red and black signals. Because of the different characteristics of flooding in the northern part of the New Territories, a special announcement on flooding in the northern New Territories due to heavy rain was also introduced.

To enhance the capability on rainstorm forecasting, a high-resolution numerical weather prediction system was under development. An operational system to assimilate radar, satellite and rainfall information and to predict the rainfall situation in the next couple of hours was developed to provide operational guidance to forecasters.

The Observatory operates tide gauges for monitoring coastal flooding and raised sea levels caused by tropical cyclones. To probe the atmosphere aloft, radiosondes carried by balloons are launched four times a day at King's Park to relay weather information from the upper air.

The Observatory exchanges weather radar images with the Guangdong Meteorological Bureau and operates four solar-powered automatic weather stations at Huangmao Zhou, Tuoning Islands, Neilingding Islands and Wailingding Islands to give earlier indication and better timing of the approach of hazardous weather such as fronts, squall lines and tropical cyclones. Using guidance from numerical products from both global and limited area models, forecasters can now issue weather forecasts several days ahead with reasonable confidence.