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September was especially hazy and wet, with a record number of hours of reduced visibility observed at Hong Kong International Airport, and above-average rainfall. The month also saw the first Strong Wind Signal No 3 warning this year.
The northeast monsoon and approaching tropical cyclones accounted for much of the haze. The airport observed 237 hours of reduced visibility in the month, the highest for September since 1997.
Typhoon Damrey brought much of the excess precipitation. The 352.6 millimetres of rainfall in the month was 52.9 mm above normal. Accumulated rainfall since January 1 was 3,196.8 mm - about 59% more than the normal figure of 2,007.1 mm.
The first two days of the month were fine, hot and hazy. The weather grew cloudy with thundery showers on September 3 and 4 as an area of low pressure affected the south China coastal areas. On September 4, a man was swept away by sea waves whipped up by the gusty easterly winds around Shek O.
Continental airstream brings week of haze
A continental airstream brought mainly fine and hazy conditions on September 5. Apart from a few isolated showers, hazy conditions continued for the next week. Visibility at Hong Kong International Airport dropped below 2,000 metres on September 11 and 12.
The outer rain band of a tropical depression over Vietnam brought some showers to Hong Kong on September 13.
With a ridge of high pressure over southeastern China, the weather turned fine on September 14 and remained so for two days.
On September 17, a ridge of high pressure over southeastern China coupled with Tropical Storm Vicente over the South China Sea triggered occasionally strong local winds and some squally showers.
Winds and showers continued on September 18 as Vicente drifted northwest towards the northern part of Vietnam. During the poor weather, two men drowned while swimming in the rough sea in Sai Kung.
Damrey triggers first No 3 signal of the year
Sunny weather returned for three days when a ridge of high pressure set in on September 19. Standby Signal No 1 was issued on the morning of September 22 when Tropical Storm Damrey entered the South China Sea.
With the air descending and warming up ahead of Damrey, it was hot and hazy on September 22. The maximum temperature rose to 34.3 degrees Celsius that afternoon, the highest in the month.
As Damrey continued to strengthen and move across the northern part of the South China Sea, the Observatory issued the first Strong Wind Signal No 3 this year on the morning of September 24. Damrey intensified into a typhoon on September 25 and made landfall over Hainan Island in the early morning of September 26.
Locally, the weather started to deteriorate in the evening of September 23. Strong winds and squally heavy showers buffeted the territory for two days. More than 100mm of rainfall were recorded in some parts of the territory on September 25.
As Damrey moved in, an intense northeast monsoon set in and maintained the windy and showery weather on September 26. Although local winds abated gradually during the day, it was cloudy with scattered showers on September 27.
The weather improved on September 28. It was mainly fine for the rest of the month.
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