STORMS (NORMAL PROCESSES, BUT CONSIDERED CATASTROPHIES)
I.
Two types: Hurricanes
(tropical) and Northeasters (non-tropical)
A Hurricanes – first record in NC was reported
B. As NC is a promontory, it receives more hurricanes than either VA, SC,
or GA.
C. NC averages a hurricane every 2-3 years; however, they are irregular in
distribution.
Ex. In 1950, 9-10 hurricanes impacted NC,
whereas in 1954-55, 4 impacted our area,
Hazel most important.
In 1827, 11 hurricanes. Most
experts consider the hurricane of
1761 the worst as many changes occurred on our
shoreline. New Inlet (south of Fort
Fisher and north of Bald Head) opened.
D. 1955-
Nation’s first billion dollar hurricane occurred, Diane in NC.
E. Hurricane
season – 1 June to 1 December, in NC, most storms are in August, September,
and October.
F. Dimensions
1.
Shape – round to elliptical
2.
Size – 100 miles in diameter (small) to 1000 miles in diameter (giant)
3.
Wind speed – maximum about 200 mph, usually about 10-20 miles out from
center or
eye.
Gales extend out 200-500 miles
4.
Movement – storms move at 10-60 mph
G. Sources
of damage
1.
High wind speed
2.
Sudden change in barometric pressure
3.
Storm surge
4.
Flooding
H. Saffir-Simpson
classification of hurricanes (based on #’s 1, 2, and 3 above):
Wind Speed
Damage
Scale
74-95 mph
little
1
96-110 mph
2
111-130 mph
3
131-155 mph
4
155 mph
major
5
I.
North Carolina hurricane history
1.
Sketchy before 19th Century
2.
Records best from 1883
a.
Activity varies place to place
b.
Cape Lookout to Cape Hatteras has more storms
J.
Nor’easters
1.
Extra-tropical – winter storms
2.
Important because of size and duration
3.
In excess of 850 storms impacted coast (Cape Hatteras – Nags Head)
4.
Worst storm – Ash Wednesday, March 1962 or Halloween 1991
K.
1. Dolan-Davis devised
rating scale of 5 classes based on wave power
H2D (H=height; D=duration)
2.
Return interval varied for classes from 3 days to 67 years
L.
Storm surge
1.
Most dangerous aspect of storm
2.
Mound of water rising above normal sea level produced by push of wind
3.
Surge level allows waves to break inland of normal location
4.
Offshore topography and shoreline configuration makes some places worse
than others
M. Factors
that control how “high” surge will be include:
1.
Astronomical tide
2.
Perigean tide/Perihelian tide
3.
Tide stage
4.
Wave height (1/2)
5.
Wave run up
N.
Storm surge disasters
1.
Worst areas are those that are flat
2.
Delta shoreline