SINGAPORE – A “tornado” that was spotted in Tuas on Monday morning was a waterspout, say experts.

Dr David Taylor, a professor of geography at the National University of Singapore, said: “It’s a waterspout – a tornado that forms either over water or originates on land and then moves over water.

“Tornadic waterspouts occur around Singapore occasionally, associated with powerful thunderstorms. They are generally no stronger than the weakest tornadoes that form over land and remain land-based.

“As with tornadoes that form and remain over land, they form as a result of spinning air currents tied-up with the instability (wind shear) associated with a thunderstorm.

“Initially, the air spins horizontally within the cloud, parallel with the land/water surface. The spin can become vertical, dropping below the cloud – leading to a tornado.”

The Meteorological Service Singapore (MSS) said intense thunderstorms were observed over the sea west of Tuas, near the Tuas Port construction site, between 9am and 10am on Monday.

It added that a waterspout typically lasts about 10 minutes, but larger ones can last for up to an hour. They dissipate rapidly near the coast or when approaching land.

“Moisture from the sea supports the growth of the thunderstorm cloud,” said MSS.

“While waterspouts are usually weaker than tornados, they can pose some risk to people conducting water sports and activities, as well as to small vessels, and can cause objects to be blown about.”

A local media outlet reported on Monday that the weather phenomenon lifted an object that supposedly weighed 100kg and dragged it 20m to 30m away from its original position.

In response to ST’s queries, the Maritime and Port Authority of Singapore (MPA) said there was “no damage to construction equipment on site and no injury to personnel”.

“The waterspout lasted for about eight minutes and construction workers who were working on site took shelter immediately after being alerted to the waterspout,” it added.