A strange weather phenomenon in Kuching

ON June 13, 2023, a good friend of mine sent me a series of photos of a phenomenon that he had observed in the early evening skies when leaving his office at Borneo International School in Kuching. He asked me, “What is this?” As an amateur meteorologist, my initial response was that it looked like a waterspout!

Upon further research, I have decided that it could have been a waterspout or a landspout, tuba (funnel) cloud, or simply the airport testing its floodlight systems. That very same day, a car passenger shot a video of a fast moving waterspout approaching Penang Bridge in Peninsular Malaysia until his/her vision was swamped with a deluge of water!

Waterspouts

In a publication of 1806, Benjamin Franklin sketched a superb, annotated image of a waterspout which is really a funnel of air containing an intense vortex. Sometimes these are destructive with a small horizontal centre occurring over a sea, large river, or lake. Mostly found in the tropics, they have been observed around the coast of the British Isles, in the Mediterranean Sea, the Baltic Sea, off the East coast of Australia and on the American/Canadian Great Lakes. They tend to be confined to within 100km of the coast. There are two types: the tornado waterspout and the fair-weather variety.

Tornadic waterspouts usually begin as tornadoes over land and they are associated with a thunderstorm and move over water. Developing on the surface of the water, they climb upwards in association with the warm temperature and high humidity in the lowest thousand metres of the atmosphere. Usually they are small, short lived (lasting between two and 20 minutes), not that dangerous, but can be large and cause considerable destruction, moving at speeds of between 18 to 28 km per hour.

There are five stages in the formation of a waterspout:

• A dark spot with a prominent circular light-coloured disc appears on the water, surrounded by a larger dark cover of indistinguishable shape with diffused edges.
• A spiral of light and dark coloured surface bands rises from the dark spot developing on the water surface.
• A dense swirling ring of sea spray, known as a cascade, appears around the dark spot with an apparent eye not unlike that of a hurricane.
• The waterspout rises from the water surface with an outer ‘shell’ of turbulent condensed water and lifts it up to several hundred metres leaving a wake or trail on the water surface as it moves.
• The waterspout decays as the funnel and vortex begins to dissipate because of an inflow of warmer air.

In short, the optimum conditions for waterspouts are related to warm water temperatures surrounded by colder and moist air and low wind speeds. Despite their names, they do not draw up water and can mostly be defined as weak columns of air over water. They are closely related to the overlying cloud type, forming under fair weather cumulus clouds or in the tornadic type under cumulonimbus or cumulus congestus clouds.

Landspouts

An American meteorologist, Howard Blumstein, coined this word in 1985 for a type of small tornado that forms during the early growth of a cumulonimbus or a cumulus congestus cloud. They are caused by down drafts from the overlying cloud and take the form of narrow condensation funnels which occur when a thunderstorm cloud is in the process of formation. Usually, they last for less than 15 minutes and decay when torrential rain falls from the cloud.

Little is in fact known about these phenomena, but their smooth tubular shape is a sight to behold. Often, they form in lines or groups of several landspouts, raising short columns of dust and other material lifted from the ground surface. It is conceivable that the spinning action originates from the rough surfaces over which they move.

Tuba or funnel clouds

These are, as their name suggests, narrow tubular or conical clouds which hang down from a more massive higher cumulonimbus or cumulus congestus cloud but they do not touch the land’s surface below. The colours of funnel clouds may vary between white and dark grey depending upon the light. Full of condensed water droplets and associated with a rotating column of air, they appear from the cloud base as strong downdrafts. If they touch the ground, they then become landspouts and waterspouts. The lifetime of these funnels is but a few minutes.

Conclusion

It is extremely difficult to determine which of these three features my friend observed in Kuching. His photographs were taken between 6.30pm and 6.35pm. There was no rain, however it could be a waterspout advancing inland from the sea and at that time of day the sea surface would be comparatively warmer than the land temperature, but it dissipates with seemingly five or six trails, which makes me think that it was a dying fair-weather waterspout that has migrated inland!

Whatever occurred in Kuching on that early evening is very likely to happen again. It had rained earlier that afternoon so dust created by building sites would have dampened down, thus a dust devil or tornado are out of the question.

I am still somewhat perplexed and would genuinely welcome suggestions from readers and professional meteorologists.