ENG-1992 — Page 418

THE ENVIRONMENT

The Year's Weather

With an extreme rainfall surplus during the first seven months of the year and a contrasting record dry spell from August to November, the annual rainfall for 1992 amounted to 2 678.8 millimetres, 21 per cent above the annual mean of 2 214.3 millimetres.

Seven consecutive wet months from January to July produced a record-breaking 2 410.6 millimetres of rainfall, more than the normal amount for the whole year. There were several episodes of heavy rain in March, April and May. A disastrous rainstorm on May 8 led to the introduction of the new rainstorm alert/warning system. The Red and Black Rainstorm Warnings were first issued during the heavy rain brought by Tropical Storm Faye on July 18. July was a month of frequent tropical cyclone activity, with tropical cyclone warning signals being raised for three storms over a period of 12 days.

A four-month drought lasted from August to November with a record low total rainfall of 201.8 millimetres during the period. Tropical cyclones were conspicuously absent in the vicinity of Hong Kong and as a result, tropical cyclone rainfall in 1992 was only slightly more than half of normal. The tendency of the tropical cyclones to track northwards east of Taiwan led to some very hot conditions in August and September.

Despite the fact that January was relatively sunny, the monthly rainfall of 40.0 millimetres was 70 per cent above the January normal of 23.4 millimetres. A substantial portion of the month's rain fell on January 5 during a spell of active winter monsoon. The dominance of the winter monsoon was reflected by the unusually high monthly mean pressure of 1 022.2 hectopascals (hPa), the sixth highest on record for January.

February was generally gloomy and damp. The active winter monsoon, alternating between the northerlies and the easterlies, brought a prolonged spell of clouds, rain and mist for most part of the month. The monthly rainfall of 142.8 millimetres was nearly three times the February normal of 48.0 millimetres and produced the sixth wettest February on record. The total duration of sunshine in February was only about two-thirds of normal.

March was still damp and wet. Clouds and mist were prevalent as moisture converged upon the south China coastal areas. The monthly mean relative humidity was as high as 90 per cent, making it the most humid March since 1978. The monthly rainfall of 242.4 millimetres was over three and a half times the March normal of 66.9 millimetres. Half of the month's rain fell on March 3 during the approach of an active cold front. It was the second wettest March day on record. The total rainfall in the first quarter of the year was the second highest on record.

Prolonged heavy downpours affected Hong Kong in April and hail was reported in Causeway Bay and Pokfulam Village on April 4. With a monthly rainfall total of 492.2 millimetres, it was the wettest April since observations began in 1884. Rain was heaviest on April 10 with a daily total of 160.7 millimetres - the second highest for a single day in April. As the wet anomaly persisted, the accumulated rainfall finally exceeded the previous record by the end of April.

May was another wet and unsettled month. Against a background of storm clouds and rain, the duration of bright sunshine for the whole month was a meagre total of 93.8 hours, the fifth lowest ever for May. A very intense and disastrous rainstorm occurred on May 8 due to the effects of an active trough of low pressure in the vicinity of Hong Kong. The hourly rainfall of 109.9 millimetres at the Royal Observatory between 6 and 7 am that day was the highest ever recorded. The daily rainfall of 324.1 millimetres on May 8 rendered it

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