•        Hurricanes pose the greatest risk for a widespread natural disaster in the Mid-Atlantic
    region during the months of August, September and October.

  •        The East Coast is in an active hurricane cycle, which began in 1995. Active cycles
    typically last 25 to 30 years. Past patterns along the East Coast suggest several notable
    storms strike during a four or five year period, in tandem with a less active time lasting
    several years. (The 2004 through 2010 seasons were generally tranquil, with a nearly
    total absence of hurricanes making landfall between Georgia and Maine.)

  •        The Middle Atlantic states have well-defined cycles of increased hurricane activity.
    It's as if someone turns on or off a faucet. Previous active cycles in the region occurred
    from 1876 until 1904 and from 1933 until 1961.The period from 1969 until 1979 brought
    the Mid-Atlantic several notable hurricane-related floods, although that timeframe is
    considered less active in the North Atlantic. (Sometimes, the Mid-Atlantic region seems to
    march to its own drummer.)

  •        The region's climate is highly cyclical. Extremes are often followed by extremes. A
    drought, for example, may be followed by a hurricane-related flood. A period of years with
    little widespread severe storm activity is often followed by two or three years with several
    destructive storms affecting large sections of the Mid-Atlantic. These may include
    hurricanes and winter nor'easters.

  •         Although August, September and October are often regarded as the peak of the
    hurricane season, the Middle Atlantic states have not experienced a significant October
    hurricane since Hazel in 1954. Before then, destructive October hurricanes tended to
    batter the region once or twice each decade and October's monsters--hurricanes and
    nor'easters--were part of local lore.

  •        Hurricanes that occur within a month or two of each other, in the same general
    geographic vicinity, often take roughly parallel tracks.      

  •        Coastal sections are due for a destructive hurricane. Hurricane Gloria in 1985 was
    the last to cause modest to significant losses to all Mid-Atlantic shore areas, from Virginia
    to Long Island, New York. The Great Atlantic Hurricane of 1944 was the last to cause
    severe damage along the shoreline from Virginia to New Jersey. The Mid-Atlantic coast
    has had a dearth of major coastal hurricanes since the early 1960s. Similar quiet periods
    occurred from the late 1820s until the late 1870s, and for about three decades during the
    early years of the 20th century. These less active periods were followed by many violent
    hurricanes, six or more within 25 years.

  •        On rare occasions, intense hurricanes (Category 3 or stronger at landfall in North
    Carolina or while off the Mid-Atlantic coast) have produced a massive wave or series of
    waves described by those on shore as appearing like "tidal waves." These caused
    immense damage to buildings and other structures along the shoreline. Generally, the
    storm waves quickly lost momentum and losses were limited to sections within a block or
    two of the beach. Such events have occurred along sections of the Mid-Atlantic coast in
    1821, 1878, 1938, 1944 and, perhaps, at other times. The huge waves struck as the
    center of the storm made its closest passage, as easterly winds turned westerly.

  •        On rare occasions, strong tropical systems produce a wall of water a few feet high
    along the eastern shore of the Chesapeake Bay. This occurs at the leading edge of the
    wind shift to a westerly direction just after the center of circulation makes its closest
    approach. The effect occurred with Hurricane Hazel in 1954 and with other tropical
    cyclones.

  •        Interior sections are due for a highly destructive hurricane-related windstorm.
    Hurricane Hazel in 1954 was the last tropical cyclone to carry actual hurricane force (74
    mph and greater) winds through a large section of the Mid-Atlantic interior, from Virginia
    to Pennsylvania. The region's climatological  history suggests that inland hurricanes such
    as Hazel occur about twice each century. Similar events occurred in 1667, 1724, 1769,
    1775, 1821, 1878 and 1896. Highly destructive winds generally ranged roughly east-west
    in a 50 to 100 mile band in the storm's northeastern sector, although a brief period of
    higher winds sometimes occurred after the center's passage, when winds turned westerly.

  •        The popular Saffir-Simpson hurricane intensity scale understates the potential for
    wind damage in the Mid-Atlantic region. A Category 1 hurricane (sustained one-minute
    winds of 74-95 mph) can be expected to do widespread Category 2 and 3-type damage.
    Isolated areas may see Category 4-type losses. Leafy trees and other vegetation, less
    wind-resistant structures and infrastructure, as well as, perhaps, other yet to be identified
    factors are responsible for the region's wind susceptibility. Also, Saffir-Simpson estimates
    of tidal surge, particular in the Chesapeake Bay region, seem understated based on
    observations during Hurricane Isabel.

  •        Rapidly advancing hurricanes, those with forward speeds greater than 30 mph, seem
    to have a greater ability to deflect higher winds aloft down to the surface, mainly in the
    northeastern sector (when the storm is tracking in a northerly direction).  The strongest
    winds are location specific. As described by an observer in Washington, DC., after the
    great windstorm of September 1896, "In hundreds of instances a well constructed roof,
    rafters and all, was blown off, while close by very frail structures at the same height were
    uninjured." Any Category 3 or stronger hurricane making landfall from the Carolinas on
    north and accelerating above 30 mph threatens destructive winds well inland.

  •        'Major' hurricane Mid-Atlantic style: Meteorologists define a 'major' hurricane as
    possessing at least Category 3 strength (sustained winds of at least 111 mph). Because
    of the Middle Atlantic states' susceptibility to wind damage, a Category 1 hurricane
    (sustained winds of 74-95 mph) tracking through interior sections will cause major
    destruction. Furthermore, a tropical cyclone that stalls off the Mid-Atlantic coast for more
    than a day may produce major shoreline damage even if it is something less than a
    Category 3.

  •        Tropical cyclones bring great differences in rainfall and wind speeds over short
    distances. Tropical Storm Hanna (Sept 2008), for example, dumped less than two inches
    of rain to more than eight inches in the Washington, D.C., metropolitan area. Hurricane
    Isabel (Sept. 2003) lashed Washington and its suburbs with peak gusts ranging from less
    than 50 mph to nearly 80 mph. (Higher winds aloft reached the surface unevenly.)

  •       As a vigorous tropical cyclone approaches, strong easterly winds several hundred
    feet aloft occasionally sink to ground level on or near the western shore of the
    Chesapeake Bay. This results in isolated areas with gusts considerably higher than those
    experienced elsewhere in the region. During Hurricane Irene, for example, most areas
    near the bay reported peak gusts ranging from 50 to 60 mph. However, Chesapeake
    Beach, Md., had a gust of 72 mph and several areas further south in St. Marys County,
    Md., likely had gusts greater than that. During Hurricane Isabel in 2003, most areas near
    the bay had peak gusts less than 65 mph. However, Gloucester Point, Reedville and
    Gwynn Island, all within 20 miles of each other in Virginia, reported peak gusts of 91 mph,
    100 mph and 107 mph, respectively.

  •        When evaluating the severe weather risk associated with a hurricane, it is important
    to consider the possibility of violent storms in the air mass ahead of the tropical cyclone,
    in adjacent weather systems, and in the air mass behind. The worst weather may occur
    indirectly, outside the hurricane's circulation, sometimes days before or after. Tropical
    Storm Nicole in 2010 is an example, as huge rainfall occurred in the tropical flow that was
    only partially part of Nicole. In September 2011, Tropical Storm Lee disintegrated as an
    organized weather system soon after landfall in September 2011. Its remnants merged
    with other weather features to produce catastrophic flooding in part of the Mid-Atlantic
    region.

  •        The Mid-Atlantic region boasts some of the most intense short-term downpours on
    earth. A few are related to tropical cyclones. The intense rainfall does not necessarily
    correlate to elevation. Hurricane Camille, for example, dumped more than 27 inches of
    rain on sections of Nelson County, Virginia, within about five hours in August 1969.
    Thunderstorms stalled by a hurricane off the New Jersey coast bucketed Ewan, New
    Jersey, (just 20 miles south of Philadelphia) with more than 22 inches in about 10 hours
    during September 1940. (While Nelson County is mountainous, Ewan is nearly at sea
    level.)

  •        On rare occasions, for unknown reasons, remnant hurricane systems have
    regenerated while their centers of circulation were over land. All such incidents have been
    heralded by a surge in rainfall intensity, resulting in generalized and flash flooding. Some
    examples include the Great Labor Day Hurricane of 1935 and hurricanes Cleo (1964),
    Camille (1969), Agnes (1972) and Gaston (2004).

  •        A hurricane deluge is of particular concern in mountainous areas. Steep slopes in
    mountainous sections allow rapid runoff. An extreme event, such as occurred with
    Hurricane Camille, can liquefy the soil generating deadly mud flows. Meanwhile, Mid-
    Atlantic urban sections, often situated on hilly terrain, are at risk of flash flooding.
    Concrete, asphalt and other impervious surfaces reduce the absorption of rainwater,
    increasing runoff. The monsoonal downpours of a tropical cyclone can quickly turn
    destructive and deadly, as occurred with Hurricane Gaston in 2004 when it pounded the
    Richmond, Virginia., metro area with rainfall totals that topped 10 inches.

  •        Remnant systems tracking through the Mid-Atlantic region may spawn tornadoes,
    particularly in the northeastern sector (if tracking in a northerly direction). They are
    generally short-lived, with intermittent tracks usually less than five miles. Pinpointing
    where a tornado will touch down is beyond our present knowledge. Although most have
    occurred during daylight, a considerable number have prowled at night.
Regional hurricane history indicates definite characteristics and patterns. The book
Hurricanes and the Middle Atlantic States
includes the following observations: