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THE ENVIRONMENT
Spring is characterised by cloudy skies, periods of light rain or drizzle, and occasionally very humid conditions with coastal fog. Temperatures tend to fluctuate widely from day to day, but show a marked increase over the season. Autumn is usually sunny and dry and is only occasionally interrupted by tropical cyclones or outbreaks of cold air, generally making it the best time for visiting Hong Kong.
The mean annual rainfall is 2,246.4 millimetres, of which about 80 per cent falls between May and September. The wettest month of the year is June when rain occurs about two days out of three and the average monthly rainfall amounts to 457.5 millimetres. The driest month is December when the monthly average is only 25.9 millimetres and when rain usually falls on only about five days in the month. October is the sunniest month when an average of 58 per cent of possible hours of sunshine is recorded. Climatological information on Hong Kong's weather is given in Appendix 39.
The severe weather phenomena that can affect Hong Kong include tropical cyclones between May and November, strong winds from the winter monsoon between October and March, frost and ice on hills and inland in the New Territories between December and February, and thunderstorms that are most frequent from April to September. Water- spouts, hailstorms and snow are rare. Although the lowest temperature recorded at the Royal Observatory in Tsim Sha Tsui is 0°C, sub-zero temperatures are recorded at times at higher elevations and in the New Territories.
The Year's Weather
Because the summer was much wetter than normal, Hong Kong's annual rainfall amounted to 2,614.7 millimetres in 1979 – 368.3 mm above normal. However, the year's mean cloudi- ness and temperatures were close to normal.
The first quarter of the year was very warm. The mean temperature for the first three months was 18.6° Celsius which is the third highest on record. The summer was cooler and less sunny than usual. Rainfall was well above average and August and September were exceptionally wet. The last quarter of the year was sunny and very dry: the total rainfall amounted to only 11.4 mm which is the second lowest on record. Due to the very dry conditions, numerous hill fires broke out and destroyed hundreds of thousands of trees and thousands of hectares of vegetation.
There were 29 tropical cyclones over the western North Pacific and the South China Sea during 1979; for six of them tropical cyclone warning signals were hoisted in Hong Kong. The hurricane signal, No. 10, was hoisted during the passage of Typhoon Hope on August 2. The last time this signal was hoisted was for Typhoon Elsie in October, 1975. Typhoon Hope was the most severe typhoon to affect Hong Kong since Typhoon Rose in 1971. Severe Tropical Storm Mac passed over western Lantau Island during the night of Septem- ber 23. It brought gales and heavy rain to Hong Kong. The four other tropical cyclones caused strong winds in Hong Kong but damage was minimal. The rainfall associated with these four tropical cyclones, together with that from Typhoon Hope and Severe Tropical Storm Mac, amounted to more than 1,000 mm which represents nearly half of the year's summer rain.
The 1978-9 winter was mild and January, 1979, was the warmest January since 1966. There were only three days with minimum temperatures below 10°C. The month was cloudier and less sunny than normal. Although most of the month's rainfall occurred in two short spells, the total rainfall was slightly above average. The strong monsoon signal was hoisted on three occasions while low temperature warnings were issued twice. Strong northerly winds set in during the evening of January 30 and the following two mornings were very cold.