Attachments
INTRODUCTION
Apart from a short break 1940 - 1946, surface observations of meteorological elements since 1884 have been summarized and published in the Royal Observatory’s Meteorological Results, Upper-air observations began in 1947 and from then onwards the annual volumes were divided into two parts, namely Part I— Surface Observations and Part II—Upper-air Observations. In 1971, ‘Meteorological Results, Part III—Tropical Cyclone Summaries’ was introduced and the first issue of the series was concerned with tropical cyclones which formed over the western Pacific and the South China Sea in 1968.
During the period 1884 - 1939, reports on destructive typhoons were occasionally prepared and were included in the Appendices of Meteorological Results. However, since 1947, this practice was extended and information on all tropical cyclones which caused gales in Hong Kong was contained in the Annual Departmental Reports of the Director of the Royal Observatory.
Tracks of tropical cyclones in the western Pacific and the South China Sea were published in Meteorological Results, Part I up to 1967. For the period 1884 - 1960, the tracks were plotted with day circle positions only.
The day circle time varied to some extent but had remained fixed at 0000 GMT since 1944. The day circle time used in each tropical cyclone is given in the Appendix of Royal Observatory Technical Memoir No. 7. From 1961 onwards, 6-hourly intermediate positions were also shown on the tracks of all tropical cyclones.
Provisional reports on individual tropical cyclones affecting Hong Kong have been prepared since 1960; this was done in order to meet the immediate needs of the press, shipping companies and others. These reports were in cyclostyled form and were supplied on request. Initially, reports were only written on those tropical cyclones causing gale or storm signals to be hoisted in Hong Kong, but by 1968 it had become necessary to produce individual reports for every tropical cyclone for which any signal was raised.
In this publication, tropical cyclones are classified into the following four categories according to the maximum sustained winds within their circulations :
A TROPICAL DEPRESSION (T.D.) has maximum sustained winds of less than 34 knots and at this stage
the centre is often not very clearly defined and cannot always be fixed precisely.
A TROPICAL STORM (T.S.) has maximum sustained winds in the range 34 - 47 knots.
A SEVERE TROPICAL STORM (S.T.S.) has maximum sustained winds in the range 48 - 63 knots.
A TYPHOON (T.) has maximum sustained winds of 64 knots or more.
Surface wind observations are made regularly at 6 stations in the Colony. The Cheung Chau Aeronautical Meteorological Station moved to a new site where observations commenced at 1100 GMT on April 20, 1970.
The old station was located at 22°12'N, 114°02'E. Each station is equipped with a Dines pressure-tube anemo- graph incorporating a twinepen direction recorder, manufactured by R. W. Munro Limited. Quick-run mechanisms are also fitted to the anemometers at Hong Kong Airport, Waglan Island and Tate’s Cairn for recording the fine structure of the wind flow in typhoons for research purposes. Details of these stations are given below.