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The warm and humid airstream associated with a trough of low pressure over the coast of Guangdong converged with a cooler easterly airstream near the Pearl River Estuary last evening (March 30), bringing squally thunderstorms, hail, heavy rain and high winds to Hong Kong. The Hong Kong Observatory issued the Red and Black Rainstorm Warning Signals at 8.15pm and 8.40pm respectively, which were the earliest Red and Black Rainstorm Warning Signals in a year since the Rainstorm Warning System commenced in 1992.
Between 9pm and 10pm yesterday, 56 millimetres of rainfall were recorded at the Hong Kong Observatory. This was the highest hourly rainfall on record (Note 1) for the Hong Kong Observatory for March. In three to four hours, more than 100 millimetres of rainfall were recorded over widespread areas in Kowloon and the New Territories. Rainfall even exceeded 150 millimetres over Yuen Long, Tuen Mun, Tsuen Wan and Sha Tin (Figure 1). Based on the past record for March, more than 100 millimetres of rainfall registered in a day over the Hong Kong Observatory occurred only 4 times since 1884 (Table 1). Daily rainfall exceeding 100 millimetres was recorded in about four days in a year on average (Note 2).
There were also hail reports in many parts of the territory (Figure 2). Most of them reported hail with a size of about 20 to 30 millimetres. According to past records, hailstones with size of up to about 100 millimetres were reported in Hong Kong on March 19, 1981.
The aforementioned trough of low pressure over the coast of Guangdong is expected to linger around for a couple of days and the weather will remain unsettled in the region.
(Note 1) Based on hourly data ending on the hour.
(Note 2) Based on climatological data between 1981 and 2010.
Ends/Monday, March 31, 2014
Issued at HKT 22:01
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