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Friday, Dec 09, 2022

Waterspout spotted off Cheung Chau Island

Waterspout spotted off Cheung Chau Island

A waterspout was spotted in Hong Kong waters on Wednesday morning amid the thundery showers associated with the trough of low pressure affecting the vicinity of the Pearl River Estuary.
A Hong Kong Observatory monitoring station on the island of Cheung Chau detected the natural phenomenon at about 10.22am.

Reports of sightings were also received, with video clips of the waterspout widely circulated online.

According to the weather watchdog, a waterspout is a rapidly rotating columnar vortex containing water droplets linking between the base of a convective cloud and the water surface. Its wind speed is often lower than that of a tornado which occurs over land.

“As a waterspout resembles the shape of a dragon and it sometimes sucks up water, it was also dubbed as ‘dragon sucking water,’” it said.

Waterspouts were also seen near Chek Lap Kok and off Lamma Island on June 8, 2020, and in May last year, respectively.

They were most commonly seen during the rainy season between May and September.

Waterspout falls into two major categories: the first category is the more common one called “fair-weather waterspout.” This type of waterspout occurs in relatively fair weather and is not directly associated with thunderstorms.

Studies have shown that the downdrafts originating from convective clouds will spread out as they reach the sea surface, creating cold outflows. This type of waterspout tends to form in the convergence zone between the cold outflows where cool air moves over warm water. A vortex first develops on the sea surface and then extends upwards gradually. When a funnel is formed, the waterspout has reached maturity.

Besides, fair-weather waterspout has a relatively short life cycle and moving track. It generally does not persist longer than 20 minutes. It dissipates rapidly after making landfall and rarely penetrates far inland.

The secondary category is called “tornadic waterspout.” Tornadic waterspout has the same formation mechanisms and characteristics as a land-based tornado. It is often associated with severe thunderstorms and accompanied by extreme weather such as high winds and hail. It sometimes develops over land and then moves to the sea.

It differs from a fair-weather waterspout in that it develops downwards in a thunderstorm. The funnel cloud appears at the initial stage, gradually extending towards the land or sea surface.

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