ENG-1987 — Page 346

THE ENVIRONMENT

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periods of August 14 to 15 and 19 to 21 respectively. A trough of low pressure gave rise to squally thunderstorms in the evening of August 29. The associated gusts were between 60 and 80 km/h, and caused the collapse of scaffoldings in two construction sites in Kennedy Town and Shau Kei Wan.

September was also relatively dry, and the monthly total rainfall of 158.3 mm was 51 per cent below normal. The mean atmospheric pressure of 1 010.6 hPa was the third highest on record for September. Only Typhoon Gerald posed a threat to Hong Kong and required the hoisting of the Stand By Signal No. 1 from September 9 to 10. On September 21, a heavy downpour caused some minor flooding in the urban areas, while only a few millimetres of rainfall were recorded over the western part of the New Territories.

October was the third consecutive month in which the rainfall was less than the climatological average. The total rainfall of 72.7 mm was 40 per cent below normal. The mean minimum temperature of 24.2 degrees was the second highest on record for October. The only tropical cyclone that affected Hong Kong in the month was Typhoon Lynn and the Strong Wind Signal No. 3 was hoisted for the first time in the year. The associated strong gusty winds on October 24 blew down some signboards and trees.

Rainfall in November, however, was almost double the normal amount. The mean cloud amount was the highest on record for November, and the total duration of sunshine was the second lowest. But November will be mostly remembered for the spell of exceptionally strong winter monsoon at the end of the month, when many climatological records were broken.

The strong monsoon signal was hoisted at 3 p.m. on November 27, before the cold front reached Hong Kong on November 28. Enhanced by Typhoon Nina, which entered the South China Sea on November 26, the monsoon winds reached gale force offshore on November 28, leading to record mean winds of 85 km/h at Waglan Island under winter monsoon conditions in Hong Kong. A fishing vessel sank off Waglan Island, a Macau- bound jetfoil was immobilised and another Macau-bound barge and its tug boat were missing. Seven pedestrians in Wong Tai Sin were injured after losing balance in the strong winds. The Tuen Mun Highway and Castle Peak Road were littered with trees and branches, overturned motor cycles and other debris and were briefly closed to traffic. The strong winds also blew off some signboards and caused some minor injuries in other areas. A new November record was set when temperatures fell by 15.6 degrees in 24 hours, starting from 3 a.m. on November 28. A decrease of 17.4 degrees in temperature in the 48 hours between 2 a.m. on November 28 and 2 a.m. on November 30, also set a new record. November 29 and 30 were exceptionally cold by November standards. The daily mean temperature of 9.2 degrees on November 29 equalled the lowest November record set in 1922. The maximum temperatures on November 29 and 30 were both 11.2 degrees, the lowest on record for November.

December was drier than normal. Only 0.4 mm of rainfall was recorded in the month. The mean relative humidity of 60 per cent was lower than the normal figure of 69 per cent. About 200 hill fires were reported in the month, out of which 106 occurred on December 20, when the relative humidity once fell to 23 per cent at the Royal Observatory. On that day, a serious hill fire at Sham Tseng forced a complete closure of the Tuen Mun Highway. The most serious hill fire occurred in Tai Mo Shan Country Park on December 21 and more than 10 000 trees were destroyed.

Royal Observatory

The Royal Observatory was established in 1883 mainly to provide scientific information for the safe navigation of ships. In the ensuing century, the observatory has evolved in line with