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An early Black Rainstorm Warning in March

     March 2014 was characterised by gloomy weather during the first-half of the month and heavy rain episodes towards the end of the month.  While the monthly total duration of bright sunshine of 86.0 hours was slightly below normal by five per cent, there were only 5.0 hours of bright sunshine from March 1 to 15.  

     The month was also cooler and wetter than usual.  The monthly mean temperature of 18.7 degrees was 0.4 degree below the normal figure of 19.1 degrees. The total rainfall of the month was 207.6 millimetres, more than double of the normal figure of 82.2 millimetres. About 99 per cent of the monthly rainfall fell between 29 and March 31. The accumulated rainfall of 247.1 millimetres since January 1 was about 53 per cent above the normal figure of 161.3 millimetres for the same period.

     Under the influence of a maritime airstream, the weather in Hong Kong was cloudy and humid with fog on the first day of the month. A cold front moved across the coast of Guangdong on the morning of March 2. Local winds strengthened from the east with a few rain patches that afternoon. Following the passage of the cold front and with subsequent replenishments of the northeast monsoon, the weather in Hong Kong was cool, gloomy and occasionally windy with a few rain patches from March 3 to 11.  Temperatures at the Hong Kong Observatory dropped to a minimum of 13.9 degrees on the morning of March 10, the lowest of the month.

     With the return of a maritime airstream, local weather became humid with rain and fog patches on March 12. As a cold front approached the coast of Guangdong, it started off foggy on the morning of March 13, but the visibility improved gradually as drier continental air took over in the daytime. The northeast monsoon brought cooler weather to Hong Kong with rain patches over the next two days.

     With the moderation of the northeast monsoon, there were sunny periods on March 16. A maritime airstream again brought humid and foggy weather with warmer temperatures in the ensuing four days. The visibility at Waglan Island once fell below 100 metres on the morning of March 19.  

     But the battle between the cooler continental air and warmer maritime air continued as the passage of another cold front on the evening of March 20 brought fine and dry weather from March 21 to 24. Then it was the turn of maritime air to bring warm and humid conditions with coastal fog from March 25 to 27. Temperatures at the Hong Kong Observatory rose to a maximum of 27.6 degrees on March 27, the highest of the month.  

     An easterly replenishment of cooler air led to cooler, humid and foggy weather on March 28. Meanwhile, the convergence of contrasting air masses near the Pearl River Delta intensified as a trough of low pressure approached the coast of Guangdong. Showers and thunderstorms started to affect Hong Kong on March 29, and became even more intense on the evening of March 30. In three to four hours, more than 100 millimetres of rainfall were recorded in Kowloon and the New Territories. Rainfall in Yuen Long, Tuen Mun, Tsuen Wan and Shatin exceeded 150 millimetres.  The hourly rainfall of 56 millimetres recorded at the Hong Kong Observatory between 9pm and 10pm on March 30 was the highest in March since record began in 1884. The Black Rainstorm Warning was issued at 8.40pm, the first time in March since the Rainstorm Warning System commenced operation in 1992. There were flooding reports in Kowloon and the New Territories including the MTR stations at Kowloon Tong and Wong Tai Sin. Intense thunderstorms also brought widespread hail and severe squalls to the territory. A maximum gust exceeding 130 kilometres per hour was reported at Lau Fau Shan, and one person was injured as stacked containers at the Kwai Chung Container Terminals toppled over. Outbreaks of heavy rain and squally thunderstorms continued throughout the night as the unsettled weather persisted till the end of the month.

     One tropical cyclone occurred over the South China Sea and the western North Pacific in the month.

     Details of issuance and cancellation of various warnings/signals in the month are summarised in Tables 1. Monthly meteorological figures and departures from normal for March are tabulated in Table 2.

Ends/Wednesday, April 2, 2014
Issued at HKT 20:55


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