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  • Heavy rain in morning of April 13

  • Wednesday, 13th April 2016

Under the influence of a trough of low pressure, the weather was unstable over the coast of Guangdong this morning (13 April) with heavy rain and squally thunderstorms. The Observatory issued the Amber Rainstorm Warning Signal at 6.30am. Afterwards, a band of intense rain and thunderstorms moved southwards across Hong Kong (Figure 1). Between 6.45am and 7.45am, rainfall over most parts of the territory exceeded 40 millimetres, and even exceeded 50 millimetres over Yuen Long, Tuen Mun and Tai Po (Figure 2). Between 7.45am and 8.45am, the rainband weakened and moved further to the southern part of Hong Kong, bringing over 30 millimetres of rainfall to the region (Figure 3). With the rainband moving to the waters south of Hong Kong, the Amber Rainstorm Warning Signal was cancelled at noon.

Amber and Red Rainstorm Warning Signals mean that heavy rain has fallen or is expected to fall generally over Hong Kong, exceeding 30 and 50 millimetres in an hour respectively, and is likely to continue. The overall rain intensity in Hong Kong this morning met the criterion of the Amber Rainstorm Warning Signal. The Observatory monitored closely the development of the rainstorm and assessed the need of issuing the Red Rainstorm Warning Signal continuously. As it was forecasted that the rainband will continue to move south away from Hong Kong, there was no need to further upgrade the rainstorm warning level. It turned out that rain with intensity over 50 millimetres per hour did not persistently affect Hong Kong generally.

Figure 1
Figure 1 Radar imageries at (a) 7.30am and (b) 8.30am showing that the rain area moved southwards across Hong Kong.

Figure 2
Figure 2 Rainfall distribution map for the hour ending 7.45am (> 50 represents regions with rainfall exceeding 50 mm in an hour)

Figure 3
Figure 3 Rainfall distribution map for the hour ending 8.45am (> 50 represents regions with rainfall exceeding 50 mm in an hour)