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Thursday, 19th September 2013

An uninvited guest during mid-autumn festival holiday

Today (19 September) is the Mid-Autumn Festival. It is followed by a long holiday. Guess you have planned to celebrate the holiday. While it will be cloudy tonight, there will be breaks in between clouds, allowing us to have glimpses of the moon while celebrating with family and friends.

You may also be aware that there is a tropical cyclone to the east of the Philippines, named Usagi. Although she is still quite far away from Hong Kong, according to the present forecast track, she is expected to cross the Luzon Strait over the weekend and approach the coast of Guangdong this Sunday (Figure 1). We expect the weather in Hong Kong to deteriorate significantly on Sunday, with high winds and seas as well as squally showers. You are advised to stay on the alert. The change in weather may affect your plan in the long holiday.

From past record, those tropical cyclones approaching the coast of Guangdong from the east via the Luzon Strait would pose a threat to Hong Kong. We should remain vigilant. Anyhow, there may still be changes to the track of Usagi. A small change in the forecast track of Usagi (yellow and blue arrows in Figure 1) may result in vastly different effects on Hong Kong's weather. For instance, if Usagi adopts a slightly northerly track (yellow arrow) and makes landfall to the east of Hong Kong, Usagi will weaken on her way to Hong Kong. We will be affected by northerly winds for a while. Due to terrain effect, the wind strength over Hong Kong will be relatively lower. In case Usagi takes a slightly southerly track (blue arrow), she will not weaken significantly on her way to Hong Kong. We will also be more prone to the effect of storm surge. As it is near the Mid-Autumn Festival, tide level is already on the high side. If storm surge does materialize, the aggregate effect of high tide and storm surge may cause flooding to low-lying areas. Anyhow, the approach of Usagi from the east will cause significant change in weather to Hong Kong this Sunday. Let's better prepare for the uninvited visit of Usagi.

Wish everyone a happy Mid-Autumn Festival!

CM Cheng

Figure 1

Figure 1      The forecast track of Usagi issued in the morning of 19 September 2013.

Last revision date: <22 Nov 2013>