ENG-1973 — Page 249

THE ENVIRONMENT

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greater extremes may occur in the New Territories where ice occasionally forms on high ground. Afternoon temperatures are usually about 5°C higher than those during the coldest part of the night.

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 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 fre- quently 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

With a total rainfall of 3,100.4 mm, more than 40 per cent above average, 1973 was the wettest year ever recorded in Hong Kong. The year was also much warmer than usual with the second highest mean temperature on record.

Twenty-two tropical cyclones were reported over the western North Pacific and the South China Sea from July to November and this was the first time since 1917 that there were no tropical cyclones over the region during the first half of the year. Of the nine typhoons and tropical storms which affected Hong Kong during the year, only Typhoon Dot came sufficiently close to cause gales and damage.

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January was slightly warmer and more cloudy than usual with rainfall more than per cent above average. Most of the month's rain fell during January 17-23 when a succession of upper air disturbances affected the south China coast. The strong monsoon signal was hoisted three times as a result of the intensification of the winter monsoon. Dry northerly air also affected Hong Kong during the month and neces- sitated the issue of the fire danger warnings on seven days.

February was the mildest on record with only half the average rainfall. Both the mean dew point and the mean minimum temperature were the highest on record for February. Relatively weak surges of the winter monsoon affected Hong Kong during the month and the strong monsoon signal was hoisted only once, for nine hours on February 20. On February 21-23, widespread coastal fog and low visibility caused 17 aircraft to divert from Hong Kong International Airport.

The abnormally warm weather of February continued during March. The mean temperature as well as the mean maximum and minimum temperatures for the month were all second highest on record for March, while the maximum temperature of 30.1°C, recorded on the last day of the month, was the highest ever recorded in any March. The month was dry with a total rainfall of only 13.3 mm. The strong mon- soon signal was hoisted twice as a result of the arrival of two monsoon surges. For