Hong Kong's climate is sub-tropical, tending towards the temperate for nearly half the year. During November and December, there are pleasant breezes, plenty of sunshine and comfortable temperatures. Many people regard these as the best months of the year.

          January and February are cloudier, with occasional cold fronts followed by dry northerly winds. Temperatures can drop below 10 degrees Celsius in urban areas but sub-zero temperatures and frost usually occur on high ground and in the New Territories.

          March and April can be very pleasant with occasional spells of high humidity. Fog and drizzle can sometimes disrupt air traffic and ferry services because of reduced visibility.

          May to August are hot and humid with occasional showers and thunderstorms, particularly during the mornings. Afternoon temperatures often exceed 31 degrees, but night temperatures generally remain around 26 degrees.

          Hong Kong is most likely to be affected by typhoons in September, although tropical cyclones of varying strength are not unusual at any time between May and November. About 31 tropical cyclones form over the western North Pacific and the China Seas every year, and about half of them reach typhoon strength with maximum winds of 118 kilometres per hour or more.

          When a tropical cyclone is about 700 to 1 000 kilometres south-east of Hong Kong, the weather is usually fine and exceptionally hot, but isolated thunderstorms sometimes occur in the evenings. If the cyclone's centre comes closer to Hong Kong, winds will increase and rain can become heavy and widespread. The heavy rain may last for a few days, and subsequent landslips and flooding sometimes cause considerably more damage than the winds.

          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 at the Hong Kong Observatory of 391.4 millimetres and on average rain falls on more than half of the days. The driest month is January with 23.4 millimetres and rain falls only about six days in the month.

          Severe weather phenomena that can affect Hong Kong include tropical cyclones, strong winter and summer monsoon winds, monsoon troughs and thunderstorms with associated squalls that are most frequent from April to September. Waterspouts and hailstorms occur infrequently, while snow and tornadoes are rare.

          Climatological data are given in Appendix 55.

It was the warmest year since records began in 1884. The annual mean temperature was 24 degrees, 0.2 degrees higher than the previous record set in 1966. The annual mean daily minimum temperature of 22.1 degrees was also the highest on record. The high temperatures were the result of a relatively weak monsoon in the winter months. Under the influence of the E1 Nio effect in the first half of the year, the typhoon season started exceptionally late. The first tropical cyclone warning signal was hoisted on August 9, the latest date for hoisting this signal since World War II. Altogether, five tropical cyclones necessitated the hoisting of warning signals in the year. The annual total rainfall recorded at the Observatory was 2 564.6 millimetres, 16 per cent above normal. The Black Rainstorm Signal was issued on June 9, when a record daily rainfall for June of 411.3 millimetres was received. The mean cloud amount of 73 pre cent was the fourth-highest on record.

          January 1998 was slightly warmer than normal with above average rainfall.

          The warm weather continued into March. In particular, March 7 and 8 were extremely humid and foggy and these conditions caused severe delay and diversion of many international flights.

          April 1998 was the warmest April on record. Late-season cold surges were notably absent and temperatures stayed at or above 20 degrees on all but one day. The Amber as well as the Red Rainstorm Warning Signals were issued for the first time this year on 12 and 26 April respectively.

          May was again warmer than normal and the month saw slightly above average rainfall.

          Over twice the average rainfall was recorded in June making it the fifth-wettest June on record. 411.3 millimetres of rain fell on June 9, the highest for any day in June, and necessitated the issuance of the Black Rainstorm Warning Signal for the first time in the year. On that day, various rainstorm warnings were continuously in force for more than 18 hours, the longest since the warning system was introduced in 1992. Over 400 millimetres of rainfall were recorded in most parts of Kowloon and over 500 millimetres in Sai Kung. 118 cases of flooding and 45 cases of landslips were reported.

          The first half of the year was very unusual in that not a single tropical cyclone was found over the entire western North Pacific and the South China Sea. This broke all records since 1946.

          In sharp contrast to the very wet six months from January to June, July was dry and hot. July saw the first tropical cyclone Nichole in the South China Sea. However, she did not affect Hong Kong. This was the first time since 1946 that no tropical cyclone warning signal was displayed in Hong Kong in the first seven months of the year.

          Temperatures for the rest of 1998 were significantly higher than normal.

          In August, both the mean temperature of 29.5 degrees and the mean minimum temperature of 27.4 degrees equalled the highest records set in August 1990. Two tropical cyclones affected Hong Kong and the first signal of the year was hoisted on August 9, the latest date for hoisting this signal in post-war years.

          In October, the mean temperature of 26.1 degrees and the mean minimum temperature of 24.3 degrees were the third- and second-highest respectively for October. Two tropical cyclones necessitated the hoisting of warning signals in the month.

          Temperature records were broken again in November. Both the monthly mean temperature of 23.2 degrees and the mean minimum temperature of 21.4 degrees exceeded previous highs.

          In December, the mean temperature of 19.1 degrees and the mean minimum temperature of 17.4 degrees were the sixth- and the third-highest respectively on record for the month.