A September with less sunshine

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     With rainy weather dominating the early part of the month, September 2016 was gloomier than usual. The total duration of sunshine recorded was 135.7 hours, 36.6 hours below the normal figure of 172.3 hours and the seventh lowest on record for September. However, the month was slightly warmer than usual with a monthly mean temperature of 27.9 degrees, 0.2 degree higher than the normal figure of 27.7 degrees. The monthly total rainfall was 323.1 millimetres, slightly below the normal figure of 327.6 millimetres. The accumulated rainfall of 2264.5 millimetres for the first nine months of the year was about 1 per cent above the normal figure of 2233.1 millimetres.

     With a trough of low pressure lingering over the South China coast, the weather in Hong Kong was unstable with showers and thunderstorms on the first 10 days of the month. The showers were particularly heavy on September 1, 5 and 10 with over 30 millimetres of rainfall across the territory. With the trough of low pressure weakening gradually, there were sunny periods and a few showers on September 11.

     Under the dominance of an anticyclone over southern China, local weather became generally fine apart from a few isolated showers on September 12 and 13. Meanwhile, Super Typhoon Meranti moved across the Luzon Strait on the night of September 13 and swept across the coastal waters of southwestern Taiwan the next day. Affected by the outer subsiding air associated with Meranti, the weather in Hong Kong was very hot and dry on September 14 with temperatures rising to about 33 degrees over most parts of the territory. With Meranti making landfall near Xiamen and weakening inland, the cloud band associated with Meranti covered eastern Guangdong and there were a few isolated showers in Hong Kong on September 15.

     Under the influence of a relatively dry continental airstream, it was mainly fine, hot and dry in Hong Kong on September 16 to 18. While it remained generally fine during the day on September 19, with the northeast monsoon setting in, local weather turned cloudy with some rain that night. Affected by the northeast monsoon, the weather became cooler and rainy on September 20. Temperatures at the Hong Kong Observatory that morning fell to a minimum of 22.8 degrees, the lowest of the month. With the gradual thinning of cloud covering the south China coastal areas, the weather was mainly fine from September 21 to 26.

     Over the western North Pacific, Severe Typhoon Megi moved across Taiwan on the afternoon of September 27 and made landfall at Fujian the next morning. Megi moved westward across Fujian and weakened gradually on September 28. It degenerated into an area of low pressure over Jiangxi on the morning of September 29. Under the subsidence effect ahead of Megi, local weather was very hot and hazy on September 27, with temperatures at the Observatory reaching a maximum of 34.9 degrees, the highest of the month and the second highest on record for September. With Megi taking a more westerly track and edging closer to Guangdong, local winds strengthened from the northwest and cleared the haze on September 28. Under the influence of the northeast monsoon, it was mainly cloudy and cooler for the rest of the month.

     Seven tropical cyclones 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 Table 1. Monthly meteorological figures and departures from the normal for September are tabulated in Table 2.

Ends/Tuesday, October 4, 2016
Issued at HKT 15:55

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Table 1 (Warnings and Signals issued in September 2016)

Table 2 (Figures and Departures from Normal - September 2016)