A waterspout is an intense columnar vortex that occurs over a body of water. They are
connected to a towering cumuliform cloud or a cumulonimbus cloud. In the common form,
it is a non-supercell tornado over water. While it is often weaker than most of its
land counterparts, stronger versions spawned by mesocyclones do occur. Waterspouts do not
suck up water; they are small and weak rotating columns of air over water
While waterspouts form mostly in the tropics and subtropical areas, other areas also report
waterspouts, including Europe, New Zealand, the Great Lakes and Antarctica. Although rare,
waterspouts have been observed in connection with lake-effect snow precipitation bands.
Waterspouts have a five-part life cycle: formation of a dark spot on the water surface, spiral
pattern on the water surface, formation of a spray ring, development of the visible condensation
funnel, and ultimately decay.
Formation Waterspouts exist on a microscale, where their
environment is less than two kilometers in width. The cloud from which they develop can
be as innocuous as a moderate cumulus, or as great as a supercell. While some waterspouts
are strong and tornadic in nature, most are much weaker and caused by different atmospheric
dynamics. They normally develop in moisture-laden environments as their parent clouds are in
the process of development, and it is theorized they spin as they move up the surface boundary
from the horizontal shear near the surface, and then stretch upwards to the cloud once
the low level shear vortex aligns with a developing cumulus cloud or thunderstorm. Weak tornadoes,
known as landspouts, have been shown to develop in a similar manner. More than one waterspout
can occur in the same vicinity at the same time. As many as nine simultaneous waterspouts
have been reported on Lake Michigan. Types
Non-tornadic
Waterspouts that are not associated with a rotating updraft of a supercell thunderstorm
are known as "non-tornadic" or "fair-weather waterspouts", and are by far the most common
type. Fair-weather waterspouts occur in coastal waters and are associated with dark, flat-bottomed,
developing convective cumulus towers. Waterspouts of this type rapidly develop and dissipate,
having life cycles shorter than 20 minutes. They usually rate no higher than EF0 on the
Enhanced Fujita scale, generally exhibiting winds of less than 30 m/s.
They are most frequently seen in tropical and sub-tropical climates, with upwards of
400 per year observed in the Florida Keys. They typically move slowly, if at all, since
the cloud they are attached to is horizontally static, being formed by vertical convective
action instead of the subduction/adduction interaction between colliding fronts. Fair-weather
waterspouts are very similar in both appearance and mechanics to landspouts, and largely behave
as such if they move ashore. Tornadic
"Tornadic waterspouts", also accurately referred to as "tornadoes over water", are formed from
mesocyclonic action in a manner essentially identical to traditional land-based tornadoes
in connection with severe thunderstorms, but simply occurring over water. A tornado which
travels from land to a body of water would also be considered a tornadic waterspout.
Since the vast majority of mesocyclonic thunderstorms occur in land-locked areas of the United States,
true tornadic waterspouts are correspondingly rarer than their fair-weather counterparts
in that country. However, in some areas, such as the Adriatic, Aegean and Ionian seas, tornadic
waterspouts can make up half of the total number.
Snowspout
A winter waterspout, also known as a snow devil, an icespout, an ice devil, a snownado,
or a snowspout, is an extremely rare instance of a waterspout forming under the base of
a snow squall. The term "winter waterspout" is used to differentiate between the common
warm season waterspout and this rare winter season event. Very little is known about this
phenomenon and only six known pictures of this event exist to date, four of which were
taken in Ontario, Canada. There are a couple of critical criteria for the formation of
a winter waterspout. Very cold temperatures need to be present over a body of water warm
enough to produce fog resembling steam above the water's surface. Like the more efficient
lake-effect snow events, winds focusing down the axis of long lakes enhance wind convergence
and likely enhance their development. Climatology
Though the majority occur in the tropics, they can seasonally appear in temperate areas
throughout the world, and are common across the western coast of Europe as well as the
British Isles and several areas of the Mediterranean and Baltic Sea. They are not restricted to
saltwater; many have been reported on lakes and rivers including the Great Lakes and the
St. Lawrence River. Waterspouts are fairly common on the Great Lakes during late summer
and early fall, with a record 66+ waterspouts reported over just a seven-day period in 2003.
They are more frequent within 100 kilometers from the coast than farther out at sea. Waterspouts
are common along the southeast U.S. coast, especially off southern Florida and the Keys
and can happen over seas, bays, and lakes worldwide. Approximately 160 waterspouts are
currently reported per year across Europe, with the Netherlands reporting the most at
60, followed by Spain and Italy at 25, and the United Kingdom at 15. They are most common
in late summer. In the Northern Hemisphere, September has been pinpointed as the prime
month of formation. Waterspouts are frequently observed off the east coast of Australia,
with several being described by Joseph Banks during the voyage of the Endeavour in 1770.
Life cycle There are five stages to the waterspout life
cycle. Initially, a prominent circular, light-colored disk appears on the surface of the water,
surrounded by a larger dark area of indeterminate shape. After the formation of these colored
disks on the water, a pattern of light and dark-colored spiral bands develop from the
dark spot on the water surface. Then, a dense annulus of sea spray, called a cascade, appears
around the dark spot with what appears to be an eye. Eventually, the waterspout becomes
a visible funnel from the water surface to the overhead cloud. The spray vortex can rise
to a height of several hundred feet or more and often creates a visible wake and an associated
wave train as it moves. Eventually, the funnel and spray vortex begin to dissipate as the
inflow of warm air into the vortex weakens, ending the waterspout's life cycle.
Nautical threat Waterspouts have long been recognized as serious
marine hazards. Stronger waterspouts can be dangerous, posing threats to water craft,
aircraft and swimmers. It is recommended to keep a considerable distance from these phenomena,
and to always be on alert through weather reports. The United States National Weather
Service will often issue special marine warnings when waterspouts are likely or have been sighted
over coastal waters, or tornado warnings when waterspouts are expected to move onshore.
Research and forecasting Szilagyi Waterspout Index
The Szilagyi Waterspout Index, developed by Canadian meteorologist Wade Szilagyi, is used
to predict conditions favorable for waterspout development. The SWI ranges from −10 to
+10, where values greater than or equal to zero represent conditions favorable for waterspout
development. International Centre for Waterspout Research
The ICWR is a non governmental organization of individuals from around the world who are
interested in the field of waterspouts from a research, operational and safety perspective.
Originally a forum for researchers and meteorologists, the ICWR has expanded interest and contribution
from storm chasers, the media, the marine and aviation communities and from private
individuals. See also
Funnel cloud Landspout
Tornado Tornadogenesis
References
External links General
A series of pictures from the boat Nicorette getting impressively close to the NSW south
coast tornadic waterspout. A USA Today online article on waterspouts:
http:www.usatoday.comwspouts.htm Online waterspout article
Pictures of cold-core waterspouts over Lake Michigan on 30 September 2006. Archived from
the original on 10 March 2007. Large waterspout off southern Tongatapu, February
2014 http:aoss-research.engin.umich.edu
– WaterspoutVideo.com – The most comprehensive website with waterspout footage from the Florida
Keys. Updated often. Experimental Great Lakes Forecast
Winter waterspout A Winter Waterspout Monthly Weather Review,
February 1907. http:www.electricyouniverse.comindex.php?level=picture&id=216