An exceptionally hot September
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Under the influence of a continental airstream, the weather in Hong Kong was hazy with sunny periods and evening thunderstorms on the first day of the month. Meanwhile, a tropical depression over the northeastern part of the South China Sea intensified into a tropical storm named Mawar. Mawar lingered over the northeastern part of the South China Sea and further intensified into a severe tropical storm the next day. Drifting towards the coast of eastern Guangdong slowly on September 3, it made landfall near Shanwei and subsequently weakened into a tropical storm that night. Mawar moved across inland Guangdong on the morning of September 4 and weakened into an area of low pressure progressively during that day. Affected by the rainbands associated with Mawar, there were squally heavy showers and thunderstorms over the territory from September 2 to 4. Local winds strengthened while Mawar skirted more than 100 kilometres to the northeast of Hong Kong on the morning of September 4. Temperatures at the Hong Kong Observatory fell to a minimum of 25.3 degrees that morning, the lowest of the month.
With a southerly airstream prevailing over the coast of Guangdong and the northern part of the South China Sea, local weather was a mixture of sunshine and showers over the next six days. Under the influence of the anticyclone aloft, the weather in Hong Kong turned generally fine and hot apart from isolated showers on September 11. While it was sunny and hazy on the morning of September 12, convective activities triggered by high temperatures brought thundery showers to the territory in the afternoon. Affected by the northeast monsoon, it was mainly fine with isolated showers on September 13 and 14.
Under the dominance of the anticyclone aloft, local weather was sunny and very hot with some haze over the next five days. With the anticyclone aloft weakening gradually, there were some showers and thunderstorms on September 20 and 21. The showery activities over the northern part of the South China Sea and the coast of Guangdong brought heavy and thundery morning showers to Hong Kong over the next two days.
Meanwhile, an area of low pressure over the central part of the South China Sea intensified into a tropical depression on the night of September 23. The tropical depression moved west-northwest across the northern part of South China Sea on September 24 and made landfall over Hainan Island that night. Affected by the outer rainbands of the tropical depression, there were a few squally showers and thunderstorms on September 24. Under the dominance of the anticyclone aloft, it remained generally fine and hot from September 25 to 29. With abundant sunshine, temperatures at the Observatory soared to a maximum of 34.1 degrees on the afternoon of September 28, the highest of the month. Affected by a fresh northeast monsoon, local weather became mainly cloudy with showers and a few thunderstorms in the morning on September 30.
Six tropical cyclones occurred over the South China Sea and the western North Pacific in September 2017.
Details of issuance and cancellation of various warnings/signals in September are summarised in Table 1. Monthly meteorological figures and departures from the normal for September are tabulated in Table 2.
Ends/Wednesday, October 4, 2017
Issued at HKT 17:05
Issued at HKT 17:05
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