The Weather of September 2001

    The weather of September 2001 was warmer and wetter than usual.  The mean temperature of 28.1 degrees was 0.5 degrees above normal and ranked the fifth highest for September.  The monthly rainfall of 563.3 millimetres was 88 per cent above normal and ranked the ninth highest for the month.  Moreover, the accumulated rainfall since 1 January amounted to 3 032.2 millimetres, 51 per cent above the normal figure of 2 007.1 millimetres and ranked the third highest for the same period.

    Under the influence of a trough of low pressure along the south China coast, the month started off unsettled with thundery showers.  Heavy rain and thunderstorms during the evening of 1 September and the early morning of 2 September brought more than 100 millimetres of rainfall to many parts of the territory, necessitating the issuance of the Black Rainstorm Warning Signal.  The most seriously affected areas were Tsuen Wan, Kwai Chung, Sha Tin and the western part of Kowloon where over 200 millimetres of rainfall were recorded.  There were altogether 19 reports of flooding and 11 reports of landslide.  In heavy rain, a slope in Sai Kung collapsed, damaging a stone hut.  Eleven villagers in Tai Wai were evacuated in a landslide.  A road in Sham Shui Po subsided.  A Mass Transit Railway train was stranded in the cross-harbour tunnel between Quarry Bay and Lam Tin due to power failure after lightning struck on the exposed overhead cables.  Some 400 passengers had to walk 500 metres down the tracks to the next station.

    The trough lingered along the coast of Guangdong and continued to bring occasional heavy rain and thunderstorms to Hong Kong during the next few days.  Temperatures fell to a minimum of 24.6 degrees in heavy rain on 5 September, the lowest in the month.  Unsettled weather persisted till 8 September.

    The weather became generally fine later on 8 September as the trough moved south away from the coastal areas.  However, an area of low pressure near Hainan Island brought cloudy weather and showers to Hong Kong during the next three days.

    The weather turned mainly fine apart from isolated showers on 12 September.  Mainly fine weather continued the next day but it was cloudy with some showers again on 14 September.

    A dry continental airstream affected southern China on 15 September, bringing fine and hot weather to Hong Kong.  Under light northerly winds, it was hazy with visibility falling to below 5 000 metres over most of the areas in the morning and below 2 000 metres in the western part of the territory.  The hot and hazy weather prevailed till 19 September.  Temperatures rose to a maximum of 33.8 degrees on 19 September, the highest in the month.

    On 19 September, Tropical Storm Nari moved from Taiwan into the South China Sea off Gaoxiong and turned west.  Nari intensified into a severe tropical storm the next day and made landfall near Shantou.  It passed about 90 kilometres to the north of Hong Kong in the evening and dissipated over inland Guangdong.  During its passage, local winds were occasionally strong on high grounds and the weather became cloudy with thundery showers.

    The rain eased off on the afternoon of 21 September.  At the same time, a surge of the northeast monsoon reached Hong Kong and offshore winds strengthened.  Winds moderated the next day and the weather became fine.  Sunny and dry weather continued for the rest of the month.

    There were altogether seven tropical cyclones in the South China Sea and the western North Pacific in the month.