Typhoon signal justified as threat of gales in Hong Kong was genuine

PUBLISHED : Monday, 07 August, 2017, 4:20pm
UPDATED : Monday, 07 August, 2017, 9:55pm

I refer to the letters by Peter A. Tanner (“Storm warning but no sign of bad weather”, July 26) and Peter Lok (“Observatory has tools but won’t use them”, July 30) on Tropical Storm Roke.

Mr Tanner questioned the necessity of issuing the No 8 signal.

Tropical Cyclone Roke approached Hong Kong from our east-southeast early on July 23. Sustained gale force winds were registered at stations in Shenzhen’s Dapeng Peninsula, oil rigs, weather buoys and ships along Roke’s path. Gusts of storm force or above were recorded 20km from Hong Kong shortly before Roke’s landfall over Sai Kung.

Before the pre-No 8 special announcement (7.20am), Roke was meandering slightly and heading towards either the south or the centre of Hong Kong. On this track, the gales observed in Dapeng Peninsula could have affected many parts of the territory. The threat of Roke bringing gales to Hong Kong was genuine and the No 8 signal was justified.

Subsequently, Roke turned more to the northwest prior to making landfall over Sai Kung and then moved quickly into inland areas of Shenzhen.

It weakened rapidly and the northerly winds in Hong Kong were not too strong due to the effect of the terrain. The absence of widespread high winds in Hong Kong was due to the last-minute change in Roke’s course. Forecasting such a sudden change in a tropical cyclone’s movement is still beyond present-day technologies.

Mr Lok wrongly claimed that the Observatory did not use available technology for tropical cyclone warnings.

He asked why no reconnaissance flight was performed for Roke. The Observatory liaised with the Government Flying Services (GFS). A flight was not possible owing to other scheduled operations. Though we want to engage GFS flights for every typhoon, it is not always possible. There are various reasons, such as unavailability of aircraft and runway slots, air traffic conditions, and the weather.

Although GFS flight data was not available, we still received multiple sources of weather data, such as wind reports from Dapeng Peninsula. As I said, they indicated the existence of gale force winds near the centre of Roke.

Secondly, the Observatory did make use of Doppler weather radar data to independently corroborate the reports of gale force winds in Dapeng Peninsula.

The Observatory accords the highest priority to the safety of Hong Kong people and safeguards the public through science. We will strive to seek further improvements.

Lee Kwok-lun, scientific officer, Hong Kong Observatory