THE ENVIRONMENT
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storm signals were hoisted on 10 occasions, including seven on weekends. However, none of the storms came very close to Hong Kong and winds only once reached gale force for a few hours during Typhoon Joe.
The winter of 1979-80 was exceptionally dry. The total rainfall for the four months from October, 1979, to January, 1980, amounted to only 15.7 mm, making it the driest four- month period on record. Although temperatures were very cold at the end of January, the month as a whole was milder than usual. An intense cold front on January 29 cleared the mist and fog and caused an extremely sharp drop in temperature of more than 19°C in 40 hours. On the morning of January 31, frost was reported on Tai Mo Shan and a minimum temperature of --3.7°C was recorded there.
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Although the mean temperature for February was only 1.9°C below normal, the first 10 days of the month were very cold with daily minimum temperatures ranging from 5.5°C to 11.4°C. The cold spell which commenced on January 30 lasted for 12 days. The mean tem- perature for this period was 9.9°C making it the coldest 12-day period since January, 1900. February 9 was the coldest day of the year the Observatory recording a drop to 5.5°C, which was the lowest temperature recorded since December 14, 1975. The cold weather killed about 1,000 tonnes of fresh water fish in the New Territories. Thunderstorms in February are rare in Hong Kong and have not occurred at the Royal Observatory since 1966. However, there were thunderstorms on four of the last six days of February, 1980. The thunderstorms in the early morning of February 27 were associated with the arrival of a cold front coupled with perturbations in the upper westerly winds. They were accom- panied by violent northwesterly squalls. A Chinese passenger ferry, the Shuguang No. 401, capsized on the river Tan Jiang about 80 nautical miles west of Hong Kong, while hail – never before recorded in February was reported by a number of people residing in the Kwai Chung and Repulse Bay areas.
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March was warmer, cloudier and more humid than normal. The most significant weather event in March was the hail which fell on March 5 and 6 – setting a new record of three hailstorms in nine days. On March 5, residents in Yuen Long, Kam Tin, Tuen Mun, Tsuen Wan, Tai Mo Shan and Tai Po reported hail between 12.05 p.m. and 12.45 p.m. About 400 hectares of vegetable crops representing 12 per cent of Hong Kong's total vegetable production were damaged by the hailstones (the largest of which measured 30 mm in diameter). Hail was against reported shortly after 5 a.m. on March 6 at Kam Tin, Lam Tsuen and Yuen Chau Tsai. Coastal fog from March 1 to 9, resulted in Waglan Island reporting its longest period of consecutive foggy days since 1953. Fog was also reported inside Victoria Harbour on six of these days. A 3,139-tonne container ship ran aground in thick fog off Pak Sha Wan, Lei Yue Mun, on the morning of March 4, while 33 aircraft were diverted from Hong Kong during the entire foggy period.
April was less sunny and cloudier than usual. Widespread thunderstorms and heavy showers occurred on April 13, and mist and fog developed between April 19 to 22. The Strong Monsoon Signal was hoisted on five occasions during the month.
May was cooler with less sunshine than usual. The showers and thunderstorms on the first 11 days of the month brought 224.3 mm of rain - representing more than 80 per cent of the month's total rainfall. Severe Tropical Storm Georgia passed about 90 nautical miles to the east-southeast of Hong Kong on May 23, bringing gales (which were experienced offshore and on hilltops), however, Georgia did not bring much rain to Hong Kong.
During most of June, Hong Kong was under the influence of a pronounced and per- sistent ridge of high pressure from the Pacific anticyclone and, as a result, the month was much sunnier and hotter than usual, Maximum temperatures were above 33°C every day