Waterspouts
What Is A Waterspout?
Five Stages Of Waterspout Development
Dangers Of Waterspouts
What Is A Waterspout?
Similar in nature and most commonly referred to as a tornado, the
waterspout is a unique weather phenomenon that occurs over a body of
water. The waterspout is much like a “dust devil” in that
its formation is enhanced by unstable conditions, often created by
warm water temperatures and high humidity in the first few thousand
feet of the atmosphere above the sea surface. For this reason, waterspouts
are most likely to occur near the coastline in summer, though sometimes
a few form as early as mid-spring or as late as mid-autumn.
Waterspouts are defined as an intense vertical column, or vortex,
of low pressure that develops on the sea surface and extends upward
to a cloud base, rather than descending down from the base of clouds,
as is the case with a tornado. Occasionally, a waterspout occurs across
interior sections of land when a tornado moves over a body of water
such as a large lake. In such instances, waterspouts can be just as
devastating as their tornado counterparts on land. Waterspouts have
the potential to be extremely dangerous, with an average life cycle
ranging from two to twenty minutes, as they travel at an average speed
between ten and fifteen knots. Maximum wind speeds of hurricane force
or greater, however briefly realized, can be expected.
Five Stages Of Waterspout Development
Meteorologists have been studying the formation of waterspouts for
years. NOAA Senior Scientists have distinguished five stages of waterspout
development:
- The “dark spot” phase is a prominent circular/light-colored
disk which appears on the surface and is surrounded by a larger dark
area of indeterminate shape. While not visible to the mariner at sea
level, the presence of a dark spot and an associated funnel cloud
overhead indicate that a complete funnel is present.
- The “spiral Pattern” phase represents a pattern of light
and dark-colored bands spiraling out from the dark spot which develops
on the sea surface.
- The “spray ring” phase creates a dense swirling ring
of sea spray appearing around the dark spot with what appears to be
an “eye.” When the wind speeds reach close to 40 miles per
hour, the wind begins to disperse the spray upward in a circular pattern
known as the spray vortex.
- In the “mature vortex” phase, the waterspout, which is
now visible from the sea surface upward to the overhead cumuli form
cloud base, achieves maximum organization and intensity.
- With the “decay” phase, the funnel and spray vortex begin
to dissipate as the inflow of warm air into the vortex weakens. Frequently,
rain showers that develop nearby create a downdraft of cooler air
that accelerates the progression of the decay phase. Mariners whose
vessels have been hit by waterspouts during the decay stage have reported
being drenched with a combination of salt water and rainwater.
Dangers Of Waterspouts
Although waterspouts are weaker than the strong tornadoes over land,
they can be a real danger to boaters. One such notable incident occurred
over San Antonio Bay in Texas, around noon on May 8, 1980. A waterspout
destroyed a shrimp boat, then overturned and sank the craft.
As a result of the potential hazards created by waterspouts, boaters
and persons living along the coast should be aware of their destructive
characteristics and be sure to seek safe shelter away from the path
of the waterspout. Specifically designed NOAA weather radios are used
to provide a continuous source of weather information to the public
that severe weather awareness is available 24 hours per day.
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