11th December 2023 – (Hong Kong) The internet was buzzing with excitement today as netizens shared captivating pictures of suspected funnel clouds. One such image depicted a suspected funnel cloud spotted at the Gold Coast Hotel, while several other netizens reported multiple funnel clouds sighted in Tuen Mun. Funnel clouds, characterised by their funnel-shaped appearance and condensed water droplets, are often associated with rotating wind columns extending from the base of clouds, typically cumulonimbus or towering cumulus clouds. It’s important to note that funnel clouds do not touch the ground or water surface and are distinct from tornadoes. However, other netizens argued that it was the steam emitted from the Castle Peak Power Station.
Funnel clouds are commonly observed during supercell thunderstorms and frequently serve as a visual precursor to tornadoes, although not all funnel clouds develop into tornadoes visible to the naked eye. While tornadoes typically begin as funnel clouds, some funnel clouds do not make surface contact and are not classified as tornadoes unless confirmed by low-level radar observations. It is also worth mentioning that tornadoes can occur without an associated condensation funnel. The term “condensation funnel” can refer to either a tornadic cloud or a funnel cloud aloft, whereas “funnel cloud” specifically refers to a rotating condensation funnel that does not reach the surface. If strong cyclonic winds are connected to a cloud base, irrespective of condensation, it is considered a tornado.
Prior to a condensation funnel reaching the surface, debris swirls are often visible. Some tornadoes may only appear as debris swirls, lacking an obvious funnel cloud extending beneath the rotating cloud base throughout their lifecycle. As time progresses, the surface-level vortex intensifies, making the debris swirls and condensation more discernible.
In cloud terminology, any funnel- or inverted-funnel-shaped cloud descending from cumulus or cumulonimbus clouds is technically referred to as a “tuba,” although the terms “tuba” and “funnel cloud” are nearly synonymous. Wall clouds, another form of tuba, are frequently associated with funnel clouds within supercell storms.
Additionally, there are “cold-air funnel clouds” that are typically weaker than those produced by supercells. While cold-air funnels rarely make contact with the ground, surface-level vortices can occasionally become strong enough to briefly touch down, resulting in weak tornadoes or waterspouts.
Unlike their severe thunderstorm counterparts, cold-air funnels are often observed under partly cloudy skies following cold fronts or in association with atmospheric boundaries such as lake or sea breezes. These funnels form due to atmospheric instability, moisture, and specific weather conditions featuring cold air aloft and warmer low-level air. While they may persist for several minutes, cold-air funnels dissipate with the loss of solar heating and the onset of precipitation.
Various types of funnel clouds exist, including shear or “high-based” funnels associated with small cumulus clouds, as well as transient funnel clouds near mountains, whose formation processes remain unknown.