WHAT IS STORM SURGE?
Storm surge is perhaps the most damaging
aspect of hurricanes although inland flooding and
wind are extremely damaging as well — as we
know from experience. Tornadoes and rip cur-rents
in seawater associated with a storm, measured as
the height above the normal astronomical tide.
This is different from the storm tide, which is the
total observed seawater rise that results from the
combination of storm surge and the astronomi-cal
WHEN IS HURRICANE SEASON?
Hurricane season officially extends from June 1 to Nov. 30th. Of course,
tropical cyclones may occur anytime and have occurred as early as April and as
late as January. The peak of the hurricane season is Sept. 10. If you look at the
most damaging storms, about half occur before or after that date: Hurricane
Katrina made landfall on Aug. 25, 2005 (southern tip of Florida), and then
again on Aug. 28-29 (Louisiana and Mississippi); Hurricane Harvey on
Aug. 25, 2017; while our most destructive North Carolina hurricane landfalls
include Fran (Sept. 5, 1996), Florence (Sept. 14, 2018), Floyd (Sept. 16, 1999),
Matthew (Oct. 8, 2016), and Hazel (Oct. 15, 1954).
WHAT IS A HURRICANE OR TROPICAL CYCLONE?
According to NOAA it is “a term to describe a rotating (counter-clockwise),
organized system of clouds and thunderstorms that originates over tropical or
subtropical waters and has closed, low-level circulation.”
The classification system used for tropical storms and hurricanes is the
Saffir-Simpson Scale. Storms are named when the sustained wind speed reaches
39 mph. The tropical storm becomes a hurricane when the sustained wind speeds
reach 74 mph. You should also note that in the classification that a storm surge
height may be associated with a given category. However, it is not an official part
of the scale as surge is quite variable because of wind direction, coastline shape
and gradient, and more. Researchers are looking at the importance of rainfall as
an important determinant of storm damage with the many record-setting rain
events in the past decade including Matthew, Harvey and Florence.
are also dangerous. Storm surge is the rise
tide. This is why the most damage occurs if
the maximum storm surge occurs at high tide.
The mean range in tides at Wrightsville Beach
is about 4 feet. Storm surge is primarily caused
by the storm’s winds pushing water onshore as it
approaches, but other important factors include
storm intensity and size, speed, coastal gradi-ent
and, very importantly, the orientation of the
coastline with the track/impact of the storm. The
northeast quadrant of the storm is most damag-ing
as the wind speeds and surge are both higher
in this quadrant. This is related to the forward
momentum of the storm.
MEAN SEA LEVEL
Surge 15 ft.
17 ft. Storm tide
2 ft. Normal high tide
WATER, RATHER THAN HIGH WINDS, IS RESPONSIBLE FOR NEARLY 90% OF HURRICANE FATALITIES.
NOAA’s National Hurricane Center has an interactive web tool, the National Storm Surge Maps, which enable people
living in hurricane prone coastal areas to evaluate their risk of storm surge flooding in all five hurricane categories: