ENG-1971 — Page 285

GEOGRAPHY AND CLIMATE

207

Close liaison is maintained with all ships visiting Hong Kong and about 50 selected ships are provided with instruments by the Observatory to encourage them to transmit weather reports which are used for locating tropical cyclones and in the preparation of forecasts. About 65 weather reports are received each day from ships, through two coastal radio stations in Hong Kong. All reports received are disseminated to other centres through the World Weather Watch telecommunication network. In addition, about 5,000 weather reports from land stations and ships are received each day from other countries. They are decoded, plotted and analysed at the Royal Observatory. Special weather bulletins are broadcast for shipping and for fishermen, and all aircraft leaving Hong Kong are given briefings, written forecasts and weather charts.

One of the most important functions of the Royal Observatory is to issue warnings of tropical cyclones. Whenever a tropical depres- sion, tropical storm or typhoon is located within the region bounded by latitudes 10°-30° north and longitudes 105°-125° east, six-hourly and often three-hourly non-local warnings are issued. These provide information on the maximum winds, the position and movement of the centre and the forecast position 24 hours ahead. Reports from ships and reconnaissance aircraft and cloud pictures received at the Royal Observatory direct from meteorological satellites are used to locate the centre and evaluate the intensity of the tropical cyclone. When the Colony itself is threatened, warnings are widely dis- tributed by means of visual signals, telephone, radio and television. Statements and recommended precautions are broadcast at frequent intervals whenever local signals are displayed. The Royal Observ- atory also issues thunderstorm and heavy rain warnings, grass fire warnings and frost and low temperature warnings whenever necessary.

The Observatory's weather radar station at Tate's Cairn is equipped with a three centimetre radar for detecting showers and local rainstorms and a 10 centimetre radar for locating larger trop- ical disturbances up to 240 nautical miles away. The latter radar can also be used to estimate the intensity of rainfall and provides valuable information for forecasting as well as for local hydrological

purposes.

A new pressure-sensitive wave recorder was installed in deep water off Waglan Island in June 1971 to obtain information on the heights and periods of waves. This information is required for the construction of the High Island reservoir and is also useful for the prediction of storm surges during typhoon conditions.

Page 285Page 286