Each year over a dozen waterspouts are reported to the National Weather
Service from the coastal waters of southeast North Carolina and northeast
South Carolina. In reality there are likely many, many more waterspouts which
go unseen and unreported each year. A waterspout appears as a slender gray or
white tube extending from the cloud base to the ocean surface. They
measure thousands of feet tall and range in width at the surface from 30 to
300 feet. Although usually small in size, waterspouts make up for this
with wind speeds as strong as some hurricanes! Small boats unintentionally
encountering a waterspout can be capsized or even destroyed in only seconds.
The National Weather Service in Wilmington has begun collecting data when
waterspouts occur over the nearby coastal waters. By constructing a composite
profile of the atmosphere on days when waterspouts occur, we can begin to
understand what conditions cause waterspouts to develop. Armed with this
knowledge, we can begin to predict when waterspouts are more likely to occur
in the future. We express this potential for waterspouts on a four-tiered
scale similar to that used to express the potential for rip currents: none,
low, moderate, and high.
Waterspouts occur most commonly during the summer months when the ocean water
and the air above it have warmed from their wintertime chill. This warm and
unstable air rises into puffy cumulus clouds typical of the summertime airmass.
On days when there is little change in wind direction or speed with height,
these bubbles of rising air can organize into slender twisting columns called
waterspouts. Waterspouts may look similar to tornadoes, but the process
which forms them is very different. Traditional tornadoes that form in
powerful thunderstorms need very strong and shifting wind speeds at different
levels in the atmosphere to develop and maintain themselves. Conditions like
these would destroy the fragile circulation of a waterspout.
Wind speeds in Florida Keys waterspouts have been measured by doppler radar at
nearly 120 mph. More waterspouts occur along the Florida coastline than
anywhere else across the country. National Weather Service forecasters at
several Florida forecast offices have conducted research on waterspout
formation over the past decade. Some of the same precursor conditions were
also found to occur with Carolina waterspouts including lack of wind shear,
and high values of moisture and instability. Many Carolina waterspouts
seem to be linked to the presence of a landbreeze front during the morning
hours. A landbreeze is formed when cool night air surges offshore over
the warm ocean waters. This miniature cold front acts to scoop up the
warmer, unstable air residing over the ocean and lift it into clouds, and
eventually showers. These showers can sometimes spawn a waterspout.
When a waterspout is seen while at sea, you should immediately move at a right
angle (i.e. left or right) to the direction of movement of the waterspout.
This will take you out of the path of the waterspout and ensure your safety.
Waterspouts can sometimes cross the shoreline and cause damage inland to a
distance of up to a half mile. When a waterspout is observed moving toward the
beach, you should move immediately to a substantial structure like a hotel or
well-constructed home. Hurricane force winds can occur in a waterspout and can
severely injure or even kill unprotected people. Even for all their
destructive fury, waterspouts are fragile and quickly succumb to friction when
they move over land. Most waterspouts will dissipate after moving no more than
a half mile inland.
The National Weather Service in Wilmington will issue a special marine warning
when reliable reports are received of waterspouts. Doppler radar often does
not have the resolution to detect the small circulation associated with a
waterspout, so eyewitness reports are the best tool we have. If you observe a
waterspout, we ask that you please give us a call at (910) 762-4289. A
meteorologist will ask you for your location, the location of the waterspout,
and its estimated speed and direction of movement. If the waterspout is moving
toward land, we can also issue a tornado warning to alert beach communities of
the impending hazard.
Each year we will analyze the successes and failures of the waterspout
prediction program for the prior waterspout season. We use this information to
improve our success in the following year. Predicting waterspouts is a brand
new endeavour and will only improve as additional data is collected.