Waterspout spotted in Hong Kong Waters

19 August 2009

The Hong Kong Observatory had received four reports from the public by 5pm today (August 19) about a waterspout that occurred around 8am for a few minutes near Po Toi Island (see Figure 1). An area of convection was also indicated by the Observatory's weather radar at that time (see Figure 2). Locally, it was mainly fine today apart from localised relatively strong convection that led to the formation of showers and the waterspout.

A waterspout occurs over water, and a tornado is its equivalent over land. It usually involves a fast rotating column of air extending from the base of a convective cloud to the water surface. A rotating column of air that does not touch the water surface is called a funnel cloud, and it is made visible by cloud droplets.

Waterspouts are most commonly seen in June and July. In Hong Kong, a waterspout was last spotted on August 13, 2005. Since 1959, there have been a total of 38 cases of waterspouts and 17 cases of funnel clouds sighted within 460 kilometres (250 nautical miles) of Hong Kong.

Figure 1: Waterspout appearing near Po Toi Island (picture courtesy of Mr Lawrence Leong)
Fig. 1 Waterspout appearing near Po Toi Island (picture courtesy of Mr Lawrence Leong)

Figure 2: An image recorded by the Hong Kong Observatorys weather radar at 8am on August 19, 2009. The red circle shows the position of the waterspout.
Fig. 2 An image recorded by the Hong Kong Observatorys weather radar at 8am on August 19, 2009. The red circle shows the position of the waterspout.