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THE ENVIRONMENT
Mean relative humidity exceeds 80 per cent from mid-February until early September. November is the least humid month with a mean relative humidity of 69 per cent, but the lowest reading of 10 per cent was recorded in a January. The daily average of bright sunshine ranges from three hours in March to more than seven hours in mid-July and late October.
Gales caused by tropical cyclones may be expected from May to November but are most likely from July to September. The passage of these cyclones several times a year at varying distances from Hong Kong brings spells of bad weather with strong winds and heavy rain. Gales are experienced once a year on average, and less frequently the centre of a mature typhoon passes sufficiently close to Hong Kong to produce winds of hurricane force, endangering life and property.
The Year's Weather
Unlike the drought-ridden early sixties, Hong Kong has experienced exceptionally heavy rainfall in recent years. In particular 1973, 1975 and 1972 are respectively the wettest, the third wettest and the sixth wettest years since records began in 1884. Active troughs of low pressure in April, May and June, together with three tropical cyclones in October, brought the 1975 annual rainfall up to 3,028.7 mm-nearly 40 per cent above normal.
Out of a total of 22 tropical cyclones reported in the western North Pacific and the South China Sea during the year, seven affected Hong Kong and necessitated the hoisting of tropical cyclone warning signals. Typhoon Elsie passed about 27 miles to the south of the Royal Observatory on October 14 causing the No. 10_hurricane signal to be hoisted for the first time since 1971, when it went up for typhoon Rose. But although Elsie brought storm to hurricane force winds, little damage to property was reported and there was no loss of life.
As a result of a weak winter monsoon, the first three months of the year were mild and cloudy and the temperature never dropped below 10°C. There was some fog in February and March, and an exceptionally large number of days with cloud and drizzle in both January and March.
April was also abnormally warm. The mean temperature of 24.2°C and the mean maximum temperature of 27.3°C were both the highest on record for April, while the mean minimum temperature of 21.8°C ranked third highest on record for the same month. Heavy rain associated with two active troughs of low pressure brought a total of 345.0 mm of rain, making the month the fourth wettest April on record. The rainfall of 92.4 mm recorded between noon and 1 pm on April 30 was also a new record for April. According to reports by residents in Kwun Tong and North Point, the thunderstorms during the morning of April 28 were accompanied by hailstones. Heavy showers and thunderstorms on the last day of the month caused flooding in low-lying areas and some minor landslips.
May was warmer but much wetter and less sunny than usual. The total rainfall for the month amounted to 571.5 mm, which is nearly double the normal. The weather was mainly influenced by active troughs of low pressure near the south China coast and