ENG-1999 — Page 478

THE ENVIRONMENT

404

The mean annual rainfall ranges from around 1 300 millimetres at Waglan Island to more than 3 000 millimetres around Tai Mo Shan. About 80 per cent of the rain falls between May and September. August is the wettest month with an average rainfall of 391.4 millimetres at the Hong Kong Observatory and, on average, rain falls on more than half of the days. The driest month is January with only 23.4 millimetres of rain and six rain days on average.

Severe weather phenomena in Hong Kong include tropical cyclones, strong winter and summer monsoon winds, monsoon troughs and thunderstorms with associated squalls. Waterspouts and hailstorms occur infrequently, while snow and tornadoes

are rare.

Climatological data are given in the Appendices.

The Year's Weather

With an annual mean temperature of 23.8 degrees, 1999 was the second warmest year on record. The monthly mean temperatures for all months except May, August and December were above their respective normal figures. In the year, eight tropical cyclones necessitated the hoisting of local Tropical Cyclone Warning Signals compared to the annual average of about six. Five of the year's tropical cyclones necessitated hoisting of the No. 8 or higher signals and the last time this occurred was in 1964. Four of these tropical cyclones crossed Hong Kong, breaking the previous record of two in 1964. The Hurricane Signal, No. 10, was hoisted in September for Typhoon York and it was the first time since 1983 that this signal was hoisted. The annual rainfall amount of 2 129.1 millimetres was close to normal.

January 1999 was warmer than normal with below average rainfall.

Sunny and dry weather dominated February. The mean temperature of 18.7 degrees was the third highest for the month and the Fire Danger Warning was in force on a total of 22 days.

Warm and relatively dry weather continued into March. The accumulated rainfall of only 28.1 millimetres was recorded in the first quarter of the year against a normal of 138.3 millimetres for the same period.

April was very warm again with slightly above average rainfall. The first Tropical Cyclone Warning Signal was hoisted due to Typhoon Leo and the hoisting of the Strong Wind Signal No. 3 on April 30 was an early record.

It was cooler and drier than usual in May. The approach of Typhoon Leo necessitated hoisting of the No. 8 Northeast Gale or Storm Signal in Hong Kong on May 2. This was the earliest hoisting of a No. 8 signal in any year.

With a monthly mean temperature of 28.9 degrees, June 1999 was the warmest June on record. The Increasing Gale or Storm Signal No. 9 was hoisted on June 7 as Typhoon Maggie swept across Hong Kong in the early hours.

July was warmer and cloudier than normal with a tropical cyclone affecting Hong Kong during the month.

Typhoon Sam traversed the northeastern part of the New Territories in the evening of August 22 and necessitated the hoisting of the Gale or Storm Signal No. 8. Sam brought torrential rain to the region making it the wettest tropical cyclone to affect