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| Mid-Atlantic Hurricanes: A Closer Examination (June 2009) |
Welcome to Mid-Atlantic Hurricanes: A Closer Examination. This is a monthly
column based on the book, Hurricanes and the Middle Atlantic States. It examines
tropical cyclones (and nor'easters), as well as climate/environmental issues, from a
historical Mid-Atlantic perspective. (The next will appear about July 10.)
column based on the book, Hurricanes and the Middle Atlantic States. It examines
tropical cyclones (and nor'easters), as well as climate/environmental issues, from a
historical Mid-Atlantic perspective. (The next will appear about July 10.)
In 1972, Hurricane Agnes devastated the Middle Atlantic states. There were only four
named hurricanes that year. In September 1896, a hurricane blasted its way along nearly the
entire Eastern Seaboard, bringing many places, including Richmond, Va., and Washington
their most destructive windstorms. There were only six tropical cyclones that year. On the
other hand, some hurricane seasons have featured more than a dozen storms, yet none
affected the Mid-Atlantic. Quantity can be very misleading. Agnes, the first named tropical
cyclone of 1972, was one too many.
2. The ocean is safe for swimming. After all, the sun is shining, the hurricane is 500
miles away, and it is not expected to come here."
Hurricane generated swells can ripple out a thousand miles or more, creating deadly rip
currents. The storm's circulation is not indicative of the range of related surf. More people
have died on Mid-Atlantic beaches from hurricane-related rip currents during fair weather than
have been lost while the elements raged.
3. The National Weather Service usually gets it wrong. The hurricane won't be that
bad. We will not evacuate from our lovely oceanfront home."
Big hurricanes have been nearly absent from the Mid-Atlantic coast during the past 50
years. However, historically, they occur several times each century. So far during the current
active North Atlantic cycle, which began in 1995, no hurricane has ravaged the entire Mid-
Atlantic coast. However, a storm capable of inundating large sections of the region's barrier
islands remains historically due and will likely come as a shock to those unaware of hurricane
history.
4. "The only real threat from a hurricane to interior sections is heavy rain. Actual
hurricanes--hurricane force winds--don't happen around here."
While rare, tropical cyclones have brought hurricane-force winds well inland, causing havoc
over large geographic areas. For example, the highest recorded winds in Washington, D.C.,
and Philadelphia, Pa., occurred with the passage of hurricanes. Most sections in the eastern
third of the Mid-Atlantic region have experienced hurricane-force winds from at least one
hurricane during the past 150 years.
5. "Everyone outside a potential flood area should shelter in place. Hunker-down in
your house."
Perhaps. But if a high wind event is anticipated and the shelter has large trees or power
lines within reach, some will topple during the storm. Hurricanes are one of nature's tools for
periodically pruning trees of the Eastern Seaboard. Also, a high wind event brings the
possibility of falling chimneys or shattered windows. Before sheltering in place, consider the
type of risks (flooding, wind, etc.) and whether a shelter is secure.
6. "Nothing like this has ever happened here before."
The corollary: "This was the most violent storm in the memory of the oldest inhabitant." Big
hurricanes are rare visitors to the Mid-Atlantic, but they always return. After an absence of
decades, many denizens assume extreme hurricane events are someone else's problem. It's
as if nature delights in playing such tricks. About the time an event is considered impossible, it
happens. The Middle Atlantic states are historically due for storms with extreme winds and
coastal flooding. No doubt, when one occurs, comments like the aforesaid will be heard again.
7. "We never thought the water would get that high."
Flooding is a hallmark of hurricanes. Torrential rains stretch the limit of known floodplains
and sometimes go beyond. Debris or landslides may create artificial dams that collect water,
then suddenly give way. Extensive pavement in urban areas may create streams that funnel
water to normally dry places. Properties near tidal waterways face increasing vulnerability
because of rising seas and erosion. About 25 percent of claims from flood insurance come
from areas considered fairly safe.
Seven Risky Assumptions Made About Mid-Atlantic Hurricanes |
| --Rick Schwartz (ricschwartz@msn.com) Hurricanes and the Middle Atlantic States |
--------------------------------------------------------------------------------
The Saffir-Simpson Hurricane Scale is a 1-5 rating based on a hurricane's present
intensity. This is used to give an estimate of the potential property damage and flooding
expected along the coast from a hurricane landfall.
Wind speed is the determining factor in the scale as storm surge values are highly
dependent on the slope of the continental shelf and the shape of the coastline in the landfall
region. Note that all winds are using the U.S. one-minute average.
Wind effects in the Mid-Atlantic region will likely be more severe than those described by
the conventional scale. (The described wind effects in the Middle Atlantic region--contained in
parentheses and rated through Category 2-- are based on hurricane history and the author's
observations and opinion. Category 2 is the highest known hurricane-related wind speed to
affect the Middle Atlantic states, from Virginia on north, other than in isolated locations.)
Category One Hurricane:
Winds 74-95 mph (64-82 kt ). No significant damage to building structures. Damage
primarily to unanchored mobile homes, shrubbery, and trees. Some damage to poorly
constructed signs. (Widespread damage to windows, shingles and chimneys. Moderate to
heavy roof damage to many homes. Widespread uprooting of trees. Many tree-shaded
streets impassable. In the countryside: considerable damage to fences, frailer outbuildings
and barns; heavy crop losses. Large-scale power outages throughout urban and rural areas.)
Category Two Hurricane:
Winds 96-110 mph (83-95 kt). Some roofing material, door, and window damage of
buildings. Considerable damage to shrubbery and trees, with some trees blown down.
Considerable damage to mobile homes, poorly constructed signs, and piers. (Widespread
damage to windows, chimneys and roofs. Scattered serious structural damage, with some
flawed or weaker buildings blown down. Catastrophic loss of trees. Most tree-shaded streets
impassable. Many signs blown down. In the countryside: fences, barns, frailer outbuildings
blown down; severe crop damage. Power outages lasting several days and longer throughout
urban and rural areas.)
Category Three Hurricane:
Winds 111-130 mph (96-113 kt ). Some structural damage to small residences and utility
buildings with a minor amount of curtainwall failures. Damage to shrubbery and trees with
foliage blown off trees and large trees blown down. Mobile homes and poorly constructed
signs are destroyed. Low-lying escape routes are cut by rising water 3-5 hours before arrival
of the center of the hurricane. Flooding near the coast destroys smaller structures with larger
structures damaged by battering from floating debris. Terrain continuously lower than 5 ft.
above mean sea level may be flooded inland 8 miles (13 km) or more. Evacuation of low-lying
residences with several blocks of the shoreline may be required. Hurricanes Jeanne and Ivan
of 2004 were Category 3 hurricanes when they made landfall in Florida and in Alabama,
respectively.
Category Four Hurricane:
Winds 131-155 mph (114-135 kt ). More extensive curtainwall failures with some complete
roof structure failures on small residences. Shrubs, trees, and all signs are blown down.
Complete destruction of mobile homes. Extensive damage to doors and windows. Low-lying
escape routes may be cut by rising water 3-5 hours before arrival of the center of the
hurricane. Major damage to lower floors of structures near the shore.Terrain lower than 10 ft.
above sea level may be flooded requiring massive evacuation of residential areas as far
inland as 6 miles (10 km). Hurricane Charley of 2004 was a Category 4 hurricane that made
landfall in Charlotte County, Florida, with winds of 150 mph.
Category Five Hurricane:
Winds greater than 155 mph (135 kt). Complete roof failure on many residences and
industrial buildings. Some complete building failures with small utility buildings blown over or
away. All shrubs, trees, and signs blown down. Complete destruction of mobile homes. Severe
and extensive window and door damage. Low-lying escape routes are cut by rising water 3-5
hours before arrival of the center of the hurricane. Major damage to lower floors of all
structures located less than 15 feet above sea level and within 500 yards of the shoreline.
Massive evacuation of residential areas on low ground within 5-10 miles (8-16 km) of the
shoreline may be required. Only three Category 5 hurricanes have made landfall in the United
States since records began: The Labor Day Hurricane of 1935, Hurricane Camille (1969), and
Hurricane Andrew in August 1992. The 1935 Labor Day Hurricane struck the Florida Keys
with a minimum pressure of 892 mb--the lowest pressure ever observed in the United States.
Hurricane Camille struck the Mississippi Gulf Coast causing a 25-foot storm surge, which
inundated Pass Christian.
| The Saffir-Simpson Hurricane Scale (National Hurricane Center) |