SINGAPORE - A "whirlwind" in Tuas captured on video that made the rounds online on Friday (Sept 27) is a landspout, the first such reported occurrence in Singapore, said the weatherman.

The National Environment Agency's Meteorological Service Singapore (MSS) said the rotating column of wind was caused by the development of an intense thunderstorm under unstable atmospheric conditions.

A thunderstorm had developed over the waters off Tuas at 10.30am on Friday, subsequently moving inland at 11am.

"The moist air feeding into the intensifying storm resulted in a rotating column of winds over Gul Way around the Tuas area," said MSS.

A landspout is similar to a waterspout that develops over a water body, it added. A landspout typically has a life span of several minutes and weakens quickly when the thunderstorm matures or dissipates.

A waterspout was last sighted on May 11 this year near Singapore's southern shore, said MSS.

Experts The Straits Times spoke to said a landspout is a phenomenon observed in the initial stages of tornado formation. They said these landspouts are usually not dangerous, although items that are not properly secured could be carried up into the air by strong winds.

In a video clip of Friday's landspout posted on the SG Kay Poh Facebook page at 1.30pm, debris can be seen being lifted into the air by the strong winds in an upward, circular motion.

Another video posted online also shows strong gusts filling the interior of what appears to be a warehouse, with plastic sheets being blown around and lamps swaying in the wind.

Dr Winston Chow, an associate professor at the Singapore Management University who researches on the relationship between urban spaces and the climate, said landspouts are uncommon in Singapore.

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He said: "While these winds usually form on very hot days, they can also occur when very strong updrafts from the surface occur as thunderstorm clouds develop in size."

Dr Matthias Roth, a professor of Urban Climatology at the National University of Singapore, agreed, saying: "The 'whirlwind' seen in the video would have reached from the surface to the base of the clouds above. This happens during unsettled weather conditions, when there is a large temperature difference between the surface and the air above."

Both experts assured the public that these whirlwinds are usually low safety risks. However, injuries may result when items that are not properly secured get dislodged.

Dr Chow noted: "Landspouts that can cause damage are thankfully relatively infrequent over land. They are usually more common over water as waterspouts."

ST understands that there were no reported injuries linked to Friday's landspout.

- Additional reporting by Clara Chong