Vesipilari

Vesipilari, also known as a water spout, is a rapidly rotating column of air that is in contact with both a body of water and a cumulonimbus or towering cumulus cloud. These phenomena are essentially weak tornadoes that form over water. They are typically observed in tropical and subtropical regions, but can occur in other areas as well.

The formation of a vesipilari begins with atmospheric instability, similar to that which causes thunderstorms. As warm, moist air rises and cools, it condenses, forming clouds. If there is sufficient wind shear, meaning winds at different altitudes are blowing at different speeds or directions, a rotating updraft can develop within the cloud. This rotating column of air can then extend downwards from the cloud base towards the water's surface.

As the rotating column descends, it picks up moisture from the water, which can make it appear as a visible funnel. The waterspout itself is a weather event, not just the visible condensation funnel. While they can appear menacing, most vesipilari are relatively weak and dissipate quickly once they move over land. However, some can be strong enough to cause damage to boats and coastal structures. They are often studied by meteorologists to better understand tornado formation and atmospheric dynamics.