Post-Mangkhut chaos: an intermediate typhoon signal for clean-up work might only cause more confusion

I refer to the letter by Mr Roger Nissim (“Another storm signal would be a safe move”, September 20) on Typhoon Mangkhut in which he proposed adding an intermediate signal between tropical cyclone signals No 3 and No 8 to allow emergency remedial work to be carried out sooner.

The Hong Kong Observatory makes decisions on the issuing and lowering of tropical cyclone signals based on scientific and objective assessment of the weather. The current tropical cyclone warning system aims to inform the public of the impact of general wind conditions in Hong Kong so that precautionary measures and appropriate response actions can be taken.

In particular, the No 8 signal means that a gale or storm force wind is expected or blowing generally in Hong Kong near sea level, with a sustained wind speed of 63-117km per hour and gusts which may exceed 180km per hour, and that the wind condition is expected to persist. The No 3 signal indicates a strong wind with a sustained speed of 41-62km per hour and gusts possibly exceeding 110km per hour.

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Under the current arrangement, the observatory makes announcements about two hours before scaling up the tropical cyclone signal from No 3 to No 8, so that the community can prepare early. As far as possible, the observatory also informs the public before lowering the signal from No 8 to No 3, as was done on the occasion of Typhoon Mangkhut, so that the community can make the necessary preparations in advance, including any preparation required by public transport operators to resume services that were suspended when the No 8 signal was in force.

However, whether the weather is suitable for specific types of recovery work and how much time such work will require are bound to be subject to many other factors such as the severity and extent of damage caused by the tropical cyclone and the locations of such recovery work. The introduction of a new tropical cyclone signal between No 3 and No 8 can hardly indicate the suitability of the weather for carrying out specific recovery work and might cause unnecessary confusion among the public instead.

L ee Lap Shun, senior scientific officer, Hong Kong Observatory