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5.4.3 SEVERE STORM Powered By Docstoc
					                                           SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM


This section provides a profile and vulnerability assessment for the severe storm hazard.


This section provides profile information including: description, location and extent, previous occurrences
and losses and the probability of future occurrences.


The severe storm hazard includes hail, lightning, thunderstorms, tornadoes and wind. Other severe storms
include Nor’Easters and hurricanes/tropical cyclones, which are discussed further in Sections 5.4.1
(Nor’Easter) and 5.4.4 (Hurricane). Due to the increased susceptibility of these hazards upon Suffolk
County, they were considered major hazards that should be discussed individually within this HMP;
therefore, this section will not include information regarding historical Nor’Easter and hurricanes/tropical
cyclones events. A description of hazards categorized as Severe Storms are provided below.

Hailstorm: According to the National Weather Service (NWS), hail is defined as a showery precipitation
in the form of irregular pellets or balls of ice more than 5 millimeters in diameter, falling from a
cumulonimbus cloud (NWS, 2005). Early in the developmental stages of a hailstorm, ice crystals form
within a low-pressure front due to the rapid rising of warm air into the upper atmosphere and the
subsequent cooling of the air mass. Frozen droplets gradually accumulate on the ice crystals until, having
developed sufficient weight; they fall as precipitation, in the form of balls or irregularly shaped masses of
ice. The size of hailstones is a direct function of the size and severity of the storm. High velocity updraft
winds are required to keep hail in suspension in thunderclouds. The strength of the updraft is a function of
the intensity of heating at the Earth’s surface. Higher temperature gradients relative to elevation above the
surface result in increased suspension time and hailstone size. Hailstorms are a potential damaging
outgrowth of severe thunderstorms [Northern Virginia Regional Commission (NVRC), 2006]. They
cause over $1 billion in crop and property damages each year in the U.S., making hailstorms one of the
most costly natural disasters (Federal Alliance for Safe Homes, Inc., 2006).

Lightning: According to the NWS, lightning is a visible electrical discharge produced by a thunderstorm.
The discharge may occur within or between clouds or between a rain cloud and the ground (NWS, 2005).
The discharge of electrical energy resulting from the buildup of positive and negative charges within a
thunderstorm creates a “bolt” when the buildup of charges becomes strong enough. A bolt of lightning
can reach temperatures approaching 50,000° Fahrenheit (F). Lightning rapidly heats the sky as it flashes
but the surrounding air cools following the bolt. This rapid heating and cooling of the surrounding air
causes thunder. On average, 89 people are killed and 300 injuries occur each year due to lightning strikes
in the U.S. (NVRC, 2006).

Thunderstorm: According to the NWS, a thunderstorm is a local storm produced by a cumulonimbus
cloud and accompanied by lightning and thunder (NWS, 2005). A thunderstorm forms from a
combination of moisture, rapidly rising warm air and a force capable of lifting air such as a warm and
cold front, a sea breeze, or a mountain. Thunderstorms form from the equator to as far north as Alaska.
These storms occur most commonly in the tropics. Many tropical land-based locations experience over
100 thunderstorm days each year (Pidwirny, 2007). Although thunderstorms generally affect a small area
when they occur, they are very dangerous because of their ability to generate tornadoes, hailstorms, strong
winds, flash flooding, and damaging lightning. A thunderstorm produces wind gusts less than 57 miles
per hour (mph) and hail, if any, of less than 3/4-inch diameter at the surface. A severe thunderstorm has

        DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                    5.4.3-1
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                                           SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

thunderstorm related surface winds (sustained or gusts) of 57 mph or greater and/or surface hail 3/4-inch
or larger (NWS, 2005). Wind or hail damage may be used to infer the occurrence/existence of a severe
thunderstorm (Office of the Federal Coordinator for Meteorology, 2001).

Tornado: A tornado is a violent windstorm characterized by a twisting, funnel-shaped cloud. It is
spawned by a thunderstorm (or sometimes as a result of a hurricane) and produced when cool air
overrides a layer of warm air, forcing the warm air to rise rapidly. Tornado season is generally March
through August, although tornadoes can occur at any time of year (Federal Emergency Management
Agency [FEMA], 2004). Tornadoes tend to strike in the afternoons and evening, with over 80-percent of
all tornadoes striking between noon and midnight [New Jersey Office of Emergency Management
(NJOEM), 2006]. The average forward speed of a tornado is 30 miles per hour (mph), but can vary from
nearly stationary to 70 mph (NWS, 1995). The National Oceanic and Atmospheric Administration
(NOAA) Storm Prediction Center (SPC) indicates that the total duration of a tornado can last between a
few seconds to over one hour; however, a tornado typically lasts less than 10 minutes (Edwards, 2007).
High-wind velocity and wind-blown debris, along with lightning or hail, result in the damage caused by
tornadoes. Destruction caused by tornadoes depends on the size, intensity, and duration of the storm.
Tornadoes cause the greatest damage to structures that are light, such as residential homes and mobile
homes, and tend to remain localized during impact (NVRC, 2006).

Windstorm: According to FEMA, wind is air moving from high to low pressure. It is rough horizontal
movement of air (as opposed to an air current) caused by uneven heating of the Earth's surface. It occurs
at all scales, from local breezes generated by heating of land surfaces and lasting tens of minutes to global
winds resulting from solar heating of the Earth. The two major influences on the atmospheric circulation
are the differential heating between the equator and the poles, and the rotation of the planet. Windstorm
events are associated with cyclonic storms (e.g. hurricanes), thunderstorms and tornadoes (FEMA, 1997).

Location and Extent

Severe storms may affect the entire mitigation study area. The extent (that is, magnitude or severity) of a
severe storm is largely dependent upon sustained wind speed. Straight-line winds, winds that come out of
a thunderstorm, in extreme cases, can cause wind gusts exceeding 100 mph. These winds are most
responsible for hailstorm and thunderstorm wind damage. One type of straight-line wind, the downburst,
can cause damage equivalent to a strong tornado (NVRC, 2006).


Hailstorms are more frequent in the southern and central plain states, where the climate produces violent
thunderstorms. However, hailstorms have been observed in almost every location where thunderstorms
occur (Federal Alliance for Safe Homes, Inc, 2006). Figure 5.4.3-1 illustrates that Suffolk County and
most of New York State experience less than two hailstorms per year.

        DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                    5.4.3-2
        October 2008
                                               SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

Figure 5.4.3-1. Annual Frequency of Hailstorms in the U.S.

Source: NVRC, 2006
Note: The black circle indicates the approximate location of Suffolk County. Suffolk County experiences less than 2 hailstorms
a year.


Thunderstorms affect relatively small localized areas, rather then large regions much like winter storms,
and hurricane events (NWS, 2005). Thunderstorms can strike in all regions of the U.S.; however, they are
most common in the central and southern states. The atmospheric conditions in these regions of the
country are most ideal for generating these powerful storms (NVRC, 2006). More than 100,000
thunderstorms occur each year in the U.S., however, only about 10-percent are classified as “severe”
(NOAA, 2005). The NWS collected data for thunder days, number and duration of thunder events, and
lightening strike density for the 30-year period from 1948 to 1977. A map was produced by the NWS,
illustrating thunderstorm hazard severity in the U.S., based on the annual average number of thunder
events between 1948 and 1977 (Figure 5.4.3-2) (NVRC, 2006). This figure indicates that Suffolk County
experienced between 0 and 40 annual thunder events during this time period.

         DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                                     5.4.3-3
         October 2008
                                               SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

Figure 5.4.3-2. Average Number of Thunderstorms between 1948 and 1977 in the U.S.

Source: NVRC, 2006
Note: The black circle indicates the approximate location of Suffolk County.

NASA scientists suggest that the U.S. will face more severe thunderstorms in the future, with deadly
lightning, damaging hail and the potential for tornadoes in the event of climate change (Borenstein, 2007).
A recent study conducted by NASA predicts that smaller storm events like thunderstorms will be more
dangerous due to climate change (Figure 5.4.3-3). As prepared by the NWS, Figure 5.4.3-3 identifies
those areas, particularly within the eastern U.S. that are more prone to thunderstorms, which includes
New York State.

         DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                  5.4.3-4
         October 2008
                                           SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

Figure 5.4.3-3. Annual Days Suitable for Thunderstorms/Damaging Winds

Source: MSNBC.com, 2007


According to the NWS, an average of 800 tornadoes affects the U.S. each year. These tornadoes typically
result in approximately 80 deaths and over 1,500 injuries annually. The highest concentration of
tornadoes in the U.S. has been in Oklahoma, Texas, Kansas, and Florida, as well as the Great Plains
region of the central U.S. Tornadoes have also been observed in the central and eastern portions of the
U.S (NVRC, 2006). Figure 5.4.3-4 shows tornado activity in the U.S., between 1950 and 1998, based on
the number of recorded tornadoes per 3,700 square miles.

        DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                               5.4.3-5
        October 2008
                                               SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

Figure 5.4.3-4. Tornado Activity in the U.S.

Source: FEMA, 2006
Note: The black circle indicates the approximate location of Suffolk County. Suffolk County experiences less than one tornado
per 3,700 square miles.

New York State ranks 30th in the U.S. for frequency of tornadoes. When compared to other states on the
frequency of tornadoes per square mile, New York ranks 35th (The Disaster Center, 2007). New York
State has a definite vulnerability to tornadoes and can occur, based on historical occurrences, in any part
of the State. According to Figure 5.4.3-4, New York State experiences between 0 and 15 tornadoes per
3,700 square miles and since 1950. The State has experienced 359 tornadoes, ranging from F0 to F4 on
the Fujita-Pearson Tornado Intensity Scale. Every county in New York State has experienced a tornado
between 1950 and 2007 (New York State Disaster Preparedness Commission [NYSDPC], 2008).
According to the New York State Hazard Mitigation Plan (NYS HMP), Suffolk County has experienced
20 tornado events between 1950 and 2007 (NYSDPC, 2008). Details regarding historical tornado events
are discussed in the next section (Previous Occurrences and Losses) of this profile.

The magnitude or severity of a tornado was originally categorized using the Fujita Scale (F-Scale) or
Pearson Fujita Scale introduced in 1971, based on a relationship between the Beaufort Wind Scales (B-
Scales) (measure of wind intensity) and the Mach number scale (measure of relative speed). It is used to
rate the intensity of a tornado by examining the damage caused by the tornado after it has passed over a
man-made structure (Tornado Project, Date Unknown). The F-Scale categorizes each tornado by
intensity and area. The scale is divided into six categories, F0 (Gale) to F5 (Incredible) (SPC, 2007).
Table 5.4.3-1 explains each of the six F-Scale categories.

         DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                                    5.4.3-6
         October 2008
                                            SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

Table 5.4.3-1. Fujita Damage Scale

                 Wind Estimate
  Scale                                                  Typical Damage

                                         Light damage. Some damage to chimneys;
    F0                 < 73              branches broken off trees; shallow-rooted trees
                                         pushed over; sign boards damaged.

                                         Moderate damage. Peels surface off roofs; mobile
    F1               73-112              homes pushed off foundations or overturned;
                                         moving autos blown off roads.

                                         Considerable damage. Roofs torn off frame
                                         houses; mobile homes demolished; boxcars
    F2               113-157
                                         overturned; large trees snapped or uprooted; light-
                                         object missiles generated; cars lifted off ground.

                                         Severe damage. Roofs and some walls torn off
                                         well-constructed houses; trains overturned; most
    F3               158-206
                                         trees in forest uprooted; heavy cars lifted off the
                                         ground and thrown.

                                         Devastating damage. Well-constructed houses
                                         leveled; structures with weak foundations blown
    F4               207-260
                                         away some distance; cars thrown and large
                                         missiles generated.
                                         Incredible damage. Strong frame houses leveled
                                         off foundations and swept away; automobile-sized
    F5               261-318             missiles fly through the air in excess of 100 meters
                                         (109 yards); trees debarked; incredible
                                         phenomena will occur.
Source: NOAA, Date Unknown

Although the F-Scale has been in use for over 30 years, there are limitations of the scale. The primary
limitations are a lack of damage indicators, no account of construction quality and variability, and no
definitive correlation between damage and wind speed. These limitations have led to the inconsistent
rating of tornadoes and, in some cases, an overestimate of tornado wind speeds. The limitations listed
above led to the development of the Enhanced Fujita Scale (EF Scale). The Texas Tech University Wind
Science and Engineering (WISE) Center, along with a forum of nationally renowned meteorologists and
wind engineers from across the country, developed the EF Scale (NWS, 2007).

The EF Scale became operational on February 1, 2007. It is used to assign tornadoes a ‘rating’ based on
estimated wind speeds and related damage. When tornado-related damage is surveyed, it is compared to a
list of Damage Indicators (DIs) and Degrees of Damage (DOD), which help better estimate the range of
wind speeds produced by the tornado. From that, a rating is assigned, similar to that of the F-Scale, with
six categories from EF0 to EF5, representing increasing degrees of damage. The EF Scale was revised
from the original F-Scale to reflect better examinations of tornado damage surveys. This new scale has to
do with how most structures are designed (NWS, 2007). Table 5.4.3-2 displays the EF Scale and each of
its six categories.

         DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                 5.4.3-7
         October 2008
                                            SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

Table 5.4.3-2. Enhanced Fujita Damage Scale
      Scale                            Speed                               Type of Damage
                                                   Light damage. Peels surface off some roofs; some damage to
        EF0                            65–85       gutters or siding; branches broken off trees; shallow-rooted trees
                                                   pushed over.
                                                   Moderate damage. Roofs severely stripped; mobile homes
        EF1                            86-110      overturned or badly damaged; loss of exterior doors; windows
                                                   and other glass broken.
                                                   Considerable damage. Roofs torn off well-constructed houses;
                     Significant                   foundations of frame homes shifted; mobile homes completely
        EF2                           111-135
                      tornado                      destroyed; large trees snapped or uprooted; light-object missiles
                                                   generated; cars lifted off ground.
                                                   Severe damage. Entire stories of well-constructed houses
                                                   destroyed; severe damage to large buildings such as shopping
        EF3                           136-165      malls; trains overturned; trees debarked; heavy cars lifted off the
                                                   ground and thrown; structures with weak foundations blown
                                                   away some distance.
                                                   Devastating damage. Well-constructed houses and whole frame
        EF4                           166-200      houses completely leveled; cars thrown and small missiles
                                                   Incredible damage. Strong frame houses leveled off foundations
                      Incredible                   and swept away; automobile-sized missiles fly through the air in
        EF5                             >200
                       tornado                     excess of 100 m (109 yd); high-rise buildings have significant
                                                   structural deformation; incredible phenomena will occur.
Source: SPC, 2007

In the Fujita Scale, there was a lack of clearly defined and easily identifiable damage indicators. The EF
Scale takes into account more variables than the original F-Scale did when assigning a wind speed rating
to a tornado. The EF Scale incorporates 28 damage indicators (DIs), such as building type, structures,
and trees. For each damage indicator, there are 8 degrees of damage (DOD), ranging from the beginning
of visible damage to complete destruction of the damage indicator. Table 5.4.3-3 lists the 28 DIs. Each
one of these indicators has a description of the typical construction for that category of indicator. Each
DOD in every category is given an expected estimate of wind speed, a lower bound of wind speed, and an
upper bound of wind speed.

Table 5.4.3-3. Enhanced F-Scale Damage Indicators

 Number       Damage Indicator       Abbreviation        Number       Damage Indicator         Abbreviation

                                                                        School - 1-story
              Small barns, farm
    1                                     SBO               15        elementary (interior           ES
                                                                        or exterior halls)

              One- or two-family                                        School - jr. or sr.
    2                                    FR12               16                                     JHSH
                 residences                                               high school

              Single-wide mobile                                      Low-rise (1-4 story)
    3                                    MHSW               17                                      LRB
                home (MHSW)                                                  bldg.

                Double-wide                                              Mid-rise (5-20
    4                                    MHDW               18                                      MRB
                mobile home                                               story) bldg.

         DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                              5.4.3-8
         October 2008
                                             SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

 Number       Damage Indicator        Abbreviation        Number       Damage Indicator      Abbreviation

                  Apt, condo,
                                                                       High-rise (over 20
     5           townhouse (3              ACT               19                                  HRB
                stories or less)

                                                                       Institutional bldg.
     6               Motel                  M                20        (hospital, govt. or         IB
                Masonry apt. or                                          Metal building
     7                                     MAM               21                                  MBS
                    motel                                                  system
               Small retail bldg.                                       Service station
     8                                     SRB               22                              Suffolk County
                 (fast food)                                               canopy
              Small professional                                       Warehouse (tilt-up
     9         (doctor office,             SPB               23         walls or heavy           WHB
                branch bank)                                               timber)
                                                                       Transmission line
    10             Strip mall               SM               24                                   TLT
               Large shopping                                            Free-standing
    11                                     LSM               25                                  FST
                     mall                                                      tower
               Large, isolated                                         Free standing pole
    12        ("big box") retail           LIRB              26            (light, flag,         FSP
                     bldg.                                                  luminary)
    13                                     ASR               27         Tree - hardwood           TH
             Automotive service
    14                                     ASB               28         Tree - softwood           TS
Source:   NOAA, 2007


Figure 5.4.3-5 indicates how the frequency and strength of windstorms impacts the U.S. and the general
location of the most wind activity. This is based on 40 years of tornado history and 100 years of
hurricane history, collected by FEMA. States located in Wind Zone IV have experienced the greatest
number of tornadoes and the strongest tornadoes (NVRC, 2006). Suffolk County is located in Wind Zone
II with speeds up to 160 miles per hour. The County is also located within the Hurricane Susceptibility
Region, which extends along the northeastern coastline of the U.S. (FEMA, 2006). The NYS HMP
identifies counties most vulnerable to wind, as determined by a rating score. Counties accumulate points
based on the value of each vulnerability indicator, the higher then indication for wind exposure the more
points assigned, resulting in a final rating score. Suffolk County was given a rating score of 19, a high
vulnerability to wind exposure. Suffolk County has the highest ranking in the State (NYSDPC, 2008).

          DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                          5.4.3-9
          October 2008
                                               SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

Figure 5.4.3-5. Wind Zones in the U.S.

Source: FEMA, 2006
Note: The black circle indicates the approximate location of Suffolk County.

Previous Occurrences and Losses

Many sources provided historical information regarding previous occurrences and losses associated with
severe storms throughout New York State and Suffolk County. With so many sources reviewed for the
purpose of this HMP, loss and impact information for many events could vary depending on the source.
Therefore, the accuracy of monetary figures discussed is based only on the available information
identified during research for this HMP.

Severe storms are frequent events for Suffolk County. However, data provided by FEMA on Presidential
Declared Disasters identifies that no Presidential or Emergency Declarations specifically associated with
severe storm events, excluding hurricanes or Nor’Easters, were reported for the Suffolk County. Based
on all sources researched, many severe storm events have impacted Suffolk County, as summarized in
Table 5.4.3-4. With severe storm documentation for New York State being so extensive, not all sources
may have been identified or researched. Hence, Table 5.4.3-4 may not include all events that have
occurred throughout the region.

Table 5.4.3-4. Severe Storm Events Between 1950 and 2007

       Event Date / Name                  Location            Losses / Impacts     Source(s)

          Winds / Hail
                                         Long Island                  NA         New York Times
       February 13, 1894
       Heavy Rain / TSTM
                                        Multi-County                  NA         New York Times
        August 25, 1903

         DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                               5.4.3-10
         October 2008
                                         SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

     Event Date / Name              Location           Losses / Impacts                   Source(s)

      TSTM / Lightning
                                   Multi-County                 NA                     New York Times
       May 28, 1916
       Tornado (F0)
                                  Suffolk County               NA               NOAA-NCDC, The Tornado Project
     September 8, 1958
                                   Long Island                $100 K                      SHELDUS
      August 30, 1960
                                  Suffolk County       $50 K – 19 injuries                SHELDUS
     September 8, 1969
       Tornado (F2)                 Closest to          $50 to $500 K in
    September 27, 1970              Huntington             damages
       Tornado (F1)                 Closest to                                  NOAA-NCDC, City-data.com, The
    September 18, 1973               Babylon                                          Tornado Project
                                  Multi-County               $166 K                       SHELDUS
     December 2, 1974
       Tornado (F1)
                                  Suffolk County               NA               NOAA-NCDC, The Tornado Project
      August 10, 1979
       Tornado (F1)
                                  Suffolk County        Approx. $250 K          NOAA-NCDC, The Tornado Project
      August 5, 1981
       Tornado (F0)
                                  Suffolk County               NA               NOAA-NCDC, The Tornado Project
      August 25, 1982
       Tornado (F1)
                                  Suffolk County               NA               NOAA-NCDC, The Tornado Project
      August 30, 1985
                                    Closest to
     Tornado (F2) / Hail                               $50 to $500 M in            NOAA-NCDC, The Tornado
                                  Riverhead and
       July 10, 1989                                   damages, 1 injury             Project, City-data.com
        Tornado (F1)
                                  Suffolk County               NA               NOAA-NCDC, The Tornado Project
August 19, 1991 (2 tornadoes)
                                    Commack                  1 injury                    NOAA-NCDC
      August 13, 1993
        Tornado (F0)               N. Babylon,                                    SHELDUS, NOAA-NCDC, The
                                                      $ 500 K in damages
        July 23, 1995             Suffolk County                                       Tornado Project
            TSTM                   Cold Spring
                                                             1 fatality                  NOAA-NCDC
    November 11, 1995                 Harbor
     TSTM/Winds/Hail              Babylon, Deer
                                                            5 injuries              SHELDUS, NOAA-NCDC
        July 18, 1997                  Park
        Tornado (F0)
                                    Fire Island                NA                        NOAA-NCDC
       June 26, 1997
          Lightning              (Brookhaven),
                                                      $100 K in damages                  NOAA-NCDC
      February 12, 1998             Southold -
                                 Suffolk County
          Lightning              Greenport, East
                                                                NA                       NOAA-NCDC
      February 18, 1998              Hampton
          Lightning              East Hampton
                                                            4 injuries                   NOAA-NCDC
        June 2, 1998                (Setauket)
                                   Selden (F0),
Tornado (1-F0 and 2-F1)/Hail
                                  Ronkonkoma                    NA                       NOAA-NCDC
  June 30, 1998 (3 events)
                                  (F1), Mt Sinai
        TSTM / Hail              West Babylon,
                                                       1 fatality, 2 injuries            NOAA-NCDC
     September 7, 1998              Copiague
                                    Closest to
        Tornado (F2)
                                  Southold and         $1 M in damages                   NOAA-NCDC
       August 8, 1999

      DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                         5.4.3-11
      October 2008
                                                SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

       Event Date / Name                   Location            Losses / Impacts                     Source(s)

                                        (From Mattituck
                                        to New Suffolk)
                                         Southampton               4 injuries                      NOAA-NCDC
          March 11, 2000
            TSTM / Hail
                                          Stony Brook               1 injury                       NOAA-NCDC
           June 2, 2000
           Tornado (F1)
                                           Southold                    NA                          NOA-NCDC
       September 15, 2000
                                           Riverhead                   NA                          NOAA-NCDC
           May 25, 2001
        Tornado (F0) / Hail            Hampton Bays,
                                                                       NA                          NOAA-NCDC
      July 1, 2001 (2 events)          Shinnecock Hills
                                         Port Jefferson             1 injury                       NOAA-NCDC
           May 21, 2002
                                            Babylon                    NA                 Long Island Hurricane History
          April 1-3, 2005
                                            Bellport                1 injury                       NOAA-NCDC
            July 5, 2006
               Tornado                                         minor damage - $         NOAA-NCDC, NWS, John Borris,
            August 25, 2006                                        unknown               Long Island Hurricane History

                                            Babylon                    NA                 Long Island Hurricane History
        October 28, 2006

             Strong Wind
                                        Suffolk County                $1 K                         NOAA-NCDC
            March 3, 2007

                                           Riverhead                   NA                          NOAA-NCDC
             June 1, 2007

             Tornado (F1)
                                          Islip Terrace                NA                          NOAA-NCDC
             July 18, 2007

            TSTM / Wind
                                         Wading River                  NA                          NOAA-NCDC
            March 5, 2008
Note (1):            The intensity of tornado events to affect Suffolk County is measured by the Fujita Scale, which was
                     decommissioned on February 2007. NOAA-NCDC storm query indicated that Suffolk County has
                     experienced 243 severe storm events between January 1, 1950 and May 31, 2008 (including TSTM, Hail,
                     Wind/Lightning, and Tornado events). However, not all of these events were identified in this table due to
                     their minor impact upon the county and/or participating townships/villages of this HMP.
Note (2):            Monetary figures within this table were U.S. Dollar (USD) figures calculated during or within the
                     approximate time of the event. If such an event would occur in the present day, monetary losses would be
                     considerably higher in USDs as a result of inflation.
DR                   Federal Disaster Declaration
EM                   Federal Emergency Declaration
F                    Fujita Scale (F0 – F5)
FEMA                 Federal Emergency Management Agency
HMP                  Hazard Mitigation Plan
K                    Thousand ($)
M                    Million ($)
NA                   Not Available
NOAA-NCDC            National Oceanic Atmospheric Administration – National Climate Data Center
NRCC                 Northeast Regional Climate Center
NWS                  National Weather Service
SHELDUS              Spatial Hazard Events and Losses Database for the United States
TSTM                 Thunderstorm
USDA                 U.S. Department of Agriculture

            DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                                5.4.3-12
            October 2008
                                           SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

Further descriptions of particular severe storm events, excluding hurricanes, tropical storms and
Nor'Easters, that have impacted Suffolk County are provided for selected events where details regarding
their impact were available. These descriptions are provided to give the reader a context of the severe
storm events that have affected the County and to assist local officials in locating event-specific data for
their municipalities based on the time and proximity of these events. Tropical storm events are separately
discussed in Sections 5.4.1 (Nor’Easters) and 5.4.4 (Hurricanes).

Monetary figures within the event descriptions were U.S. Dollar (USD) figures calculated during or
within the approximate time of the event (unless present day recalculations were made by the sources
reviewed). If such an event would occur in the present day, monetary losses would be considerably
higher in USDs as a result of inflation.

February 13, 1894 (Strong winds, hail): A rough snowstorm hit Long Island, brining hail and strong
winds. May of the lighthouses could not be seen. The ocean was very loud and could be heard for miles.
Parts of Suffolk County were affected as well, especially in East Moriches and Sag Harbor (New York
Times, 1894).

In East Moriches, two men were walking back to the Beach View Hotel. The road that crosses the marsh
to get back to the hotel was exposed to full force gale winds and was covered with water and floating ice.
Several times during their trip back to the hotel, their feet were lifted off the ground and were almost
washed out to the ocean. The men made it back safely to the hotel (New York Times, 1894).

In Sag Harbor, the strong winds caused the steamer Montauk to break loose from its moorings. The
steamer pounded against a bulkhead all day, creating a noise that could be heard for over a mile. The
steamer could not be removed from the bulkhead until the winds died down (New York Times, 1894).
Monetary losses were not documented in the materials available for review.

May 28, 1916 (Strong winds, heavy rain): An electrical storm hit the Hudson Valley and New York
City area, causing power outages throughout the area. In Sag Harbor, a cloudburst caused severe damage,
which included power outages and downed trees and power lines. A bolt of lightning struck the power
house of the Sag Harbor Electric Light and Power Company. The lighting caused an engine in the power
house to explode, causing Sag Harbor to be without power (New York Times, 1916). Monetary losses
were not documented in the materials available for review.

September 27, 1970 (Tornado): According to City-data.com, a source that compiles data from multiple
government and commercial sources, a Category 2 tornado with maximum wind speeds of 113 to 157
mph occurred on this date. The tornado was located approximately 13.7 miles from the Huntington City
Center and caused between $50,000 and $500,000 in damages.

September 18, 1973 (Tornado): According to City-data.com, a source that compiles data from multiple
government and commercial sources, a Category 2 tornado with maximum wind speeds of 113 to 157
mph occurred on this date. The tornado occurred closest to the Babylon area approximately 8.5 miles
from its city center.

July 10, 1989 (“Northeast U.S. Tornado Outbreak of 1989”): This event was a series of tornadoes
which caused more then $130 million (1989 USD) in damage across the northeastern U.S. The storm
system produced severe weather events that included hail up to 2.5 inches in diameter, thunderstorm
winds up to 90 mph, and 17 tornadoes. More than 150 people were injured and one fatality occurred as a
result of the tornado outbreak and one fatality occurred as a result of winds. Several towns in New York
State and Connecticut were especially hit hard (NCDC, 2007).

        DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                  5.4.3-13
        October 2008
                                           SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

In the New York City metropolitan area, severe thunderstorms hit across the area, spawning tornadoes,
producing large hail and destroying more than 100 homes and businesses in New York, New Jersey and
Connecticut. Throughout the region, more than 200 people were hospitalized and treated for minor
injuries (Hays, 1989).

In Suffolk County, severe lightning and a tornado affected the County. A F2 tornado struck East
Moriches, where it picked up a trailer with a person sitting in it. The trailer was tossed and thrown across
an adjacent airfield. The person in the trailer suffered minor injuries, but the trailer was destroyed. A
radio transmitter in Sag Harbor was struck with lightning (Hays, 1989; NOAA-NCDC, 2007;
Weather2000.com, 2007). Monetary losses were not documented in the materials available for review.

July 23, 1995 (Tornado): A tornado touched down in South Farmingdale, New York (eastern Nassau
County) and North Babylon, New York (western Suffolk County). The twister touched down in three
separate locations: the first two touch-downs in South Farmingdale cut a path 1/4 mile in length and 300
to 400 feet in width, while the third touched-down in North Babylon (100 yards in length and 100 feet in
width. The majority of damage was to trees, which fell on houses, cars, pools, and fences. Many sheds
were lifted and smashed to the ground and there were reports of some houses receiving roof damage. One
house had a porch ripped away. No injuries were reported (NRCC, 1995). According to NOAA-NCDC,
this F0 tornado caused $500,000 in damages in N. Babylon, due to downed trees and power lines and
damaged homes and cars.

July 18, 1997 (Thunderstorm): According to NOAA-NCDC, two "waves" of severe thunderstorms
moved southeast across the area on this date. The first line of thunderstorms moved across Nassau and
Western Suffolk Counties during the early afternoon. The second line of thunderstorms moved over the
area during the evening. For the day, these thunderstorms caused two deaths and 24 injuries. Both lines of
severe thunderstorms produced high winds. In addition, the first line produced large hail. Selected wind
gusts from Western Suffolk County that were documented with the passage of the first line include: 60
mph at both Babylon and Farmingdale Airport; and 58 mph at Bohemia. Significant structural damage
(several roofs were blown off businesses) resulted in five injuries in Deer Park. A NWS Meteorologist
investigated this damage and concluded that it was caused by a microburst. At least 3 roofs were blown
off (the K-Lombardi Repair Shop and 2 businesses on Price Parkway). In addition to the 1 inch diameter
hail observed at Babylon, 3/4-inch diameter hail occurred at Deer Park. Monetary losses were not
documented in the materials available for review.

February 12, 1998 (Lightning): According to NOAA-NCDC, a lighting event resulted in $100,000 in
structural damages to a house in Ridge (Brookhaven) and Southold. Lightning caused significant
structural damage to a house at 59 Giant Oak Road in Ridge. According to the Ridge Fire Department,
lightning struck the house. Two-by-fours in the roof exploded and struck and punctured the house next to
the one that caught fire. The second floor of this two-story Cape Cod was totally destroyed. Lightning
also struck a house on Bay Haven Road in Southold. It gouged a hole at the base of a tree and carved a
furrow across the lawn. Lightning struck the sprinkler system, hit the septic tank, ran along the pipes,
blew the cap from the waste pipe into the basement stairs (cracking them), and struck the clothes dryer
which ignited a basement fire.

February 18, 1998 (Lightning): According to NOAA-NCDC, as a warm front between two low pressure
systems moved north, it produced heavy showers and thunderstorms. Lightning struck a house at 1445
Bay Shore Road in Greenport and set it ablaze. The house was totally destroyed. Two other houses in the
Greenport area were also struck: minimal damage occurred to one house and no apparent damage
occurred to the other house. Lightning also struck a propane tank next to a house in East Hampton. It
ignited a fire that totally destroyed this house. Monetary losses were not documented in the materials
available for review.

        DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                  5.4.3-14
        October 2008
                                           SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

June 2, 1998 (Lightning): According to NOAA-NCDC, as thunderstorms moved east across Suffolk
County, they produced frequent lightning. Lightning struck a barn in East Hampton (at the Oakdale Farms
property on Three Mile Harbor Road) and sent electricity through four volunteer firemen. All four men
required hospital treatment. Lightning also struck a brick chimney in a Setauket home, causing bricks to
fall into the backyard as well as into the structure itself. Monetary losses were not documented in the
materials available for review.

June 13, 1998 (Thunderstorms): A line of thunderstorms developed and moved eastward over the area.
The storms produced heavy rains, flash flooding and frequent lightning. The heavy rain resulted in
widespread flooding of streets, poor drainage and low-lying areas, home basements, and small streams.
Lightning struck many homes, starting fires and damaging the homes (NOAA-NCDC, 2007).

In Suffolk County, rivers of moving water formed rapidly on the streets. In Mastic, water flowed quickly
from Montauk Highway into a residential area, flooding basements and first floors of homes. In Wading
River, lightning struck a television antenna of a home, which then travelled to an attic and ignited a fire.
The home was located on Zophar Mills Road (NOAA-NCDC, 2007). Monetary losses were not
documented in the materials available for review.

June 30, 1998 (Tornadoes): Two waves of severe weather affected the New York City area: one in the
morning and the other in the evening. Funnel clouds were produced in Suffolk County, described by
meteorologists as mild. The first wave included an isolated severe thunderstorm that spawned two weak
tornadoes, large hail, and damaging winds, as it moved across central Suffolk County. The first tornado
(F1) touched down near Lake Shore Road in Lake Ronkonkoma, downing many trees and power lines.
Trees were blown into houses, causing structural damage. The tornado then lifted and funnel clouds were
observed before another touchdown took place, creating an F0 tornado. This touchdown occurred on the
campus of the Suffolk Community College in Selden. Many trees were uprooted and fell on parked cars
at the campus. Widespread damage was reported across the County (NCDC, 2007).

Overall, wind speeds of up to 70 mph were at the surface and speeds between 80 and 100 mph were at
treetop level. The toppling trees caused damage to 10 homes and 12 cars. No injuries were reported
(Sutton, 1998; Gearty, 1998). Monetary losses were not documented in the materials available for

September 7, 1998 (Thunderstorm): According to NOAA-NCDC, an intense line of severe
thunderstorms oriented from north to south developed during Labor Day afternoon ahead of a strong
approaching cold front. As the storms moved east at 40 to 50 mph, they produced high winds, large hail,
and an isolated tornado. Wind gusts from 60 to 80 mph downed many trees and power lines throughout
the area. In Suffolk County, high winds overturned many boats in the Great South Bay, downed large
trees in West Babylon and Rocky Point, and downed large tree limbs in Wading River. One person died
when a thunderstorm wind gust capsized a 19-foot sail boat in Great South Bay near Copiague. A
Centerport woman, 36, and her daughter, 3, were injured when a tree fell on them in the parking lot of the
Ground Round Restaurant and CVS on Fort Salonga Road. The following peak wind gusts were reported:
72 mph in Babylon and 65 mph in Fire Island. Monetary losses were not documented in the materials
available for review (NCDC, 2007).

August 8, 1999 (Tornado): According to NOAA-NCDC and City-Data.com, an F2 tornado caused $1
million in damages and 1 injury in Mattituck to New Suffolk. A cluster of severe thunderstorms formed
north of an approaching strong warm front and moved east-southeast, just north of the front. A severe
thunderstorm produced a tornado along the south shore of the North Fork of Suffolk County on Long
Island. The tornado touched down and lifted several times along a 4 mile path as it moved east-southeast

        DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                  5.4.3-15
        October 2008
                                           SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

from just southeast of Mattituck Air Base, across Marratooka Pt., Kimogener Pt. (of New Suffolk),
Cutchogue Harbor, Central Nassau Pt., then lifted as it crossed Hog Neck Bay. NSW data indicate that the
tornado touched down first in southern sections of Mattituck. This was in the backyard area bounded to
the west by Marratooka Road, to the north by Center Street, and to the south by Park Ave. Most damage
at this location was to trees, where many tops were twisted off and several snapped off at 5 to 15 feet
above the ground. This was estimated as F1 damage. The tornado "bounced" and continued east to the dirt
road extension of Park Avenue, where it lifted the roof off a cottage. The roof of the building detached
from the house and was carried about 115 feet to the northeast. The tornado continued east for about 1/2
mile, then touched down again at 10 Kimogenor Point. It ripped off the porch and part of the main roof of
the house at this address. It apparently developed a few separate vortices at this location. One twisted a
100 year old metal windmill over high tension power lines and did some significant damage to large trees.
Another vortex slammed into the front porch at 2 Kimogenor Point and ripped off the porch and a large
section of the roof of the house. The lone inhabitant said he saw a "wall of water" heading toward his
house and instinctively dove into the stone fireplace to protect himself as the storm hit. Winds were
estimated over 100 mph over this part of the tornado's path. The tornado continued east along Jackson
Avenue, impacting many mature trees in the area (NCDC, 2007).

The most significant damage occurred in the vicinity of Jackson Avenue and Fifth Street, where winds
were estimated from 110 to 120 mph, based on the to the devastation of many large trees. This was the
area where F2 damage was observed. This was also the widest path width, estimated at 300 yards. The
tornado continued east along Jackson Avenue, creating F1 damage then went over Cutchogue Harbor.
Eyewitnesses from Nassau Point (Little Hog Neck) said they saw the tornado over the water just east of
New Suffolk. They saw several suction vortices rotating around the main funnel. The tornado moved
across Nassau Point, in the vicinity of Wunnaweta Pond, where it twisted and sheared off many trees that
fell on and damaged houses. It bounced again and hit close to the ground near #6225 and #6325 Nassau
Point Road. Many trees fell onto, and damaged, homes. These backyards were on top of a cliff
overlooking Hogs Neck Bay. The tornado lifted before hitting these homes. This was the last indication of
tornado-related damage. The latest cost estimates of damage from the Southold Supervisor's Office are in
excess of $1 million dollars. One injury occurred as a person was struck by flying debris (NCDC, 2007).

July 11, 2001 (Thunderstorms): A line of severe thunderstorms rapidly moved eastward across portions
of southeast New York State and Long Island. The line eventually developed into a “bow-echo”
structure, which produced a swath of damaging winds and dime-size hail across parts of Westchester
County, southeast New York, and Suffolk County. Wind gusts of up to 61 mph passed through Stony
Brook. The damaging winds toppled numerous large trees onto power lines and roadways, resulting in
power outages and road closures (NCDC, 2007). Monetary losses were not documented in the materials
available for review.

July 5, 2006 (Lightning): According to NOAA-NCDC, this event resulted in a 34-year-old man being
struck by lightning while erecting a fence at Frank P. Long Intermediate School. No additional
information was provided (NCDC, 2007).

August 25, 2006 (Tornado): According to Mr. Jack Boris of WCBSTV.com, an F0 Tornado with winds
of 60 to 70 mph occurred in Suffolk County on this date. There were reports of damage to trees and cars
and Con Edison reported 14,000 customers without power (Boris, 2006).

NOAA-NCDC indicated that a severe thunderstorm produced a weak F0 tornado as it moved across
extreme southeast Nassau County and extreme southwest Suffolk County. The tornado's path length was
only about ¼ mile long and its maximum path width was around 150 yards. There was significant tree
damage along its path. Rotation was evident based on impacts to the tops of many trees. The most damage
occurred in East Massapequa between Merrick Road and Route 27A, Old Sunrise Highway. It was

        DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                 5.4.3-16
        October 2008
                                              SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

concentrated around Clocks Boulevard, southeast across Melrose Avenue and County Line Road, then
across Amityville's Old Fields and Homestead Avenues. The tornado lifted into the parent cloud before
reaching South Ketcham Avenue. This severe thunderstorm produced damaging winds, large hail, and
torrential rain along its path. Large tree branches were downed in Wantagh. Quarter size hail was
reported in Farmingdale. Flash flooding also occurred along its path. Monetary losses were not
documented in the materials available for review (NCDC, 2007).

October 28, 2006 (Windstorm): A windstorm impacted sections of Babylon, New York (Figure 5.4.3-6)
(Long Island Hurricane History, 2007). Impacts and monetary losses were not documented in the
materials available for review.

Figure 5.4.3-6. October 28, 2006 Windstorm in Babylon, New York

Source: Long Island Hurricane History, 2007

Probability of Future Events

In Section 5.3, the identified hazards of concern for Suffolk County were ranked. The NYS HMP
conducts a similar ranking process for hazards that affect the State. The probability of occurrence, or
likelihood of the event, is one parameter used for ranking hazards. Based on historical records and input
from the Planning Committee, the probability of occurrence for severe storms in Suffolk County is
considered frequent [hazard event that occurs more frequently than once in 10 years (>10-1/yr), as
presented in Table 5.3-3]; however, impacts only related to severe storms, excluding those associated
with hurricanes, tropical storms and flooding, and Nor’Easters are expected to be minimal. It is estimated
that Suffolk County and all of its jurisdictions, will continue to experience severe storms annually that
may induce secondary hazards such as utility failure and transportation accidents.

         DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                5.4.3-17
         October 2008
                                           SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM


To understand risk, a community must evaluate what assets are exposed or vulnerable in the identified
hazard area. For severe storms, the entire County has been identified as the hazard area. Therefore, all
assets in Suffolk County (population, structures, critical facilities and lifelines), as described in the
County Profile section, are vulnerable to a severe storm. The following text evaluates and estimates the
potential impact of severe storms on Suffolk County including:

•   Overview of vulnerability
•   Data and methodology used for the evaluation
•   Impact, including: (1) impact on life, safety and health of county residents, (2) general building
    stock, (3) critical facilities, (4) economy and (5) future growth and development
•   Further data collections that will assist understanding of this hazard over time
•   Overall vulnerability conclusion

Overview of Vulnerability

As defined for this HMP, severe storms include hail, lightning, thunderstorms, tornadoes and windstorms.
The high winds and air speeds associated with these storm events often result in power outages,
disruptions to transportation corridors and equipment, loss of workplace access, significant property
damage, injuries and loss of life, and the need to shelter and care for individuals impacted by the events.
A large amount of damage can be inflicted by trees, branches, and other objects that fall onto power lines,
buildings, roads, vehicles, and, in some cases, people. The risk assessment for severe storm evaluates
available data for a range of storms included in this hazard category.

The entire inventory of the County is at risk of being damaged or lost due to impacts of severe storms.
Certain areas, infrastructure, and types of building are at greater risk than others due to proximity to
falling hazards and their type of construction.

Potential losses associated with high wind events were calculated for Suffolk County using HAZUS-MH
MR3 for two probabilistic wind/hurricane events, the 100-year and 500-year MRP events. The impacts
on population, existing structures, critical facilities and the economy are presented in the hurricane profile
(Section 5.4.4).

Data and Methodology

FEMA’s How-To #2 (FEMA #386-2) states there are no standard loss estimation models and tables
available to estimate losses from tornado events. FEMA does not describe methods to estimate losses
from lightning, hail, or thunderstorm events. As advised by FEMA for estimating losses for tornadoes,
national weather databases and local resources were used to collect and analyze severe storm impacts on
the County. As discussed above, HAZUS-MH was used to calculate potential losses associated with high
wind events (see the hurricane hazard profile).

Impact on Life, Health and Safety

The entire County is identified as the hazard area vulnerable to severe storms. According to the 2000 U.S.
Census, Suffolk County had a population of 1,419,369 people. This number excludes the incoming
commuter population and the seasonal population that increases in the summer months, when these

        DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                    5.4.3-18
        October 2008
                                           SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

hazard events typically occur. Per the planning department, it is estimated that the eastern Suffolk County
population (Towns of Riverhead, Southold, Shelter Island, Southampton, and East Hampton) more than
doubles during the summer. Daytime in-commuting and seasonal changes in population (the summer)
affect the total population vulnerable to this hazard and the number of residents that may evacuate, be
displaced or require temporary to long-term sheltering. Suffolk County’s current evacuation plans take
temporal changes in population into account.

Vulnerable populations, including the elderly and low income populations, are considered most
susceptible to the severe storm hazard. Socially vulnerable populations are most susceptible, based on a
number of factors including their physical and financial ability to react or respond during a hazard and the
location and construction quality of their housing. Low income residents may not have adequate housing
able to withstand high winds associated with tornadoes (i.e., mobile homes). According to FEMA, the
safest place for people during a tornado is in a safe-room or storm shelter designed to specific
performance criteria. The 2000 U.S. Census indicates that there are 5,374 mobile homes in Suffolk
County. Based on past occurrences of severe storm events in Suffolk County, injuries and loss of life
resulted from fallen trees, flying debris and electrocution from a lightning strike.

Suffolk County recognizes it has a large special needs population and is committed to providing the best
possible assistance to these citizens when an emergency is imminent. The Suffolk County Comprehensive
Emergency Management Plan outlines the Suffolk County Joint Emergency Evacuation Program (JEEP).
JEEP provides emergency evacuation assistance (shelter and transportation) to citizens that are
particularly at risk during emergency situations.

Impact on General Building Stock

The entire inventory in the County is vulnerable to severe storms. The data in HAZUS-MH MR3
estimates that there are 561,778 structures in Suffolk County, with a total building replacement value
(structure and content) of greater than $262 billion. Approximately 90-percent of the buildings and 68-
percent of the building stock structural value are associated with residential housing. Because of
differences in building construction, residential structures are generally more susceptible to wind damage
than commercial and industrial structures. Please refer to Section 4 (County Profile) which presents
building stock statistics by occupancy class for the County.

There are certain limitations to using HAZUS-MH. This plan utilized HAZUS-MH MR3 default data to
perform a HAZUS Level 1 analysis. HAZUS-MH is only intended to provide an estimation of building
replacement value, using estimates for typical buildings in a given census block. It is only as current
and/or accurate as the US Census 2000 data, and it does not reflect specific local building conditions,
such as a higher percentage of luxury structures, higher local costs to procure and transport building
materials through New York City, and the recent dramatic worldwide increases in the cost of building
construction materials and products and/or services dependent upon the price of petroleum. Plan
participants have indicated the values presented herein significantly underestimate the actual Replacement
Cost Values (RCV) in Suffolk County.

Current modeling tools are not available to estimate specific losses for this hazard, with the exception of
windstorms. Please refer to the hurricane profile (Section 5.4.3) for a detailed look at potential estimated
building values (structure and content) damaged by 100-year and 500-year MRP wind events (hurricane).

According to FEMA’s How-To #2 (FEMA #386-2), the most important factor in assessing vulnerability
to tornadoes is to examine how likely structures will fail when exposed to winds that exceed their design
or to flying debris that may penetrate the structure. “Structural damages from tornadoes are a function of
the building’s relative location to the tornado vortex, which cannot be predicted or mapped. In general,

        DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                   5.4.3-19
        October 2008
                                           SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

building damages can range from cosmetic to complete structural failure, depending upon the wind speed
and location of the building with respect to the tornado path. Only a qualified architect or structural
engineer can do more than the most rudimentary analysis of a building’s capacity to resist the effects of a
tornado.” Page 4-27 of the guidance continues to state there are no building structure and content
“…standard loss estimation models and tables for tornadoes…” The guidance advises to estimate
structure and content vulnerability and content losses based on past occurrences of tornadoes. Available
historic loss information indicates damages ranging from $50,000 to $500 Million per F0 to F2 tornado

A similar approach using historic structure and content losses to estimate damages to general building
stock due to hail, lightning and thunderstorm events was used. In the past, buildings struck by lightning
in Suffolk County have experienced minimal structural impact to total destruction (due to fire). For
thunderstorms, the only documented historic loss was three roofs blown off homes caused by a
microburst. Monetary losses documenting structural damage as a result of hail, lightning and
thunderstorm events were not found in available resources.

A specific area that may be vulnerable to the severe storm hazard is the floodplain, including low-lying
coastal zones. Thunderstorms are often accompanied by heavy rain causing flooding. Generally, losses
resulting from flooding associated with thunderstorms should be less than that associated with a 100-year
or 500-year flood. Infrastructure at risk due to flooding is presented in the flood hazard profile.

Impact on Critical Facilities

All critical facilities are considered vulnerable to the severe storm hazard. HAZUS-MH estimates the
replacement value for critical facilities and infrastructure in Suffolk County (see Section 4 – County
Profile). Because power interruption can occur, backup power is recommended.

Severe storm events may require short-term sheltering of residents. FEMA recommends that
communities assess the number, location, capacity and strength of shelters to ensure they can adequately
house displaced residents and withstand design wind spend, especially for tornado events). Currently,
Suffolk County has 127 designated shelters. The default replacement value for these shelters is $590,000
each with masonry construction. Table 4-15 lists the designated shelters in Suffolk County.

Impact on Economy

Severe storms also have impacts on the economy, including: loss of business function, damage to
inventory, relocation costs, wage loss and rental loss due to the repair/replacement of buildings. HAZUS-
MH estimates the total economic loss associated with each hurricane scenario (direct building losses and
business interruption losses). Direct building losses are the estimated costs to repair or replace the
damage caused to the building. This is reported in the Impact on General Building Stock section
discussed earlier and in Section 5.4.4 Hurricane profile. Business interruption losses are the losses
associated with the inability to operate a business because of the damage sustained during the earthquake.

According to the HAZUS-MH MR3 hurricane/wind model, for the 100-year MRP event (Suffolk County
model run), greater than $2.8 billion in business-related economic losses is estimated; a majority of which
is associated with direct building losses/property damage. Approximately $3 million is estimated in
business interruption losses for the County (e.g., loss of income, wages, relocation costs). For the 500-
year MRP hurricane/wind event (Suffolk County model run), HAZUS-MH MR3 estimates a loss of
nearly $26 billion in business-related economic losses, of which $2.8 billion is estimated in business
interruption losses.

        DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                  5.4.3-20
        October 2008
                                           SECTION 5.4.3: RISK ASSESSMENT – SEVERE STORM

The high winds associated with severe storm events often cause power outages, disruptions to
transportation corridors and equipment, and loss of workplace access, all of which impact the local
economy. Such impacts can impact heating or cooling provision to citizens (including the young and
elderly, who are particularly vulnerable to temperature-related health impacts).Additionally, damage can
also be inflicted by trees, branches, and other objects that fall onto power lines, buildings, roads, and
vehicles. Sufficient information was not available to perform a detailed assessment of estimated losses to
the economy. It is estimated that the impact to the economy, as a result of severe storm event, would be
considered “low” in accordance with the risk ranking shown in Table 5.3-4.

Future Growth and Development

As discussed in Section 4 and in each community’s annex (Volume II, Section 9), areas targeted for
future growth and development have been identified across the County. Any areas of growth could be
potentially impacted by the severe storm hazard because the entire planning area is exposed and
vulnerable. It is anticipated that the human exposure and vulnerability to severe storm impacts in newly
developed areas will be similar to those that currently exist within the County.

Additional Data and Next Steps

As defined for this plan, the severe storm event cannot currently be modeled in HAZUS-MH (tornado,
thunderstorm, etc.). However, additional detailed loss data from past and future events will assist in
assessing potential future losses. Based on these values and a sufficient number of data points, future
losses could be modeled in some fashing. Alternately, percent of damage estimates could be made and
multiplied by the inventory value to estimate potential losses. This methodology is based on FEMA’s
How To Series (FEMA 386-2), Understanding Your Risks, Identifying and Estimating Losses (FEMA
2001) and FEMA’s Using HAZUS-MH for Risk Assessment (FEMA 433) (FEMA 2004). Suffolk
County will continue to compile data and track modeling tools to identify means to refine current loss
estimates in the future. In addition, it will continue mitigation planning to be prepared for such events
and minimize their impact on humans and structures in the future.

Overall Vulnerability Assessment

Severe storms are common in the study area, often causing impacts and losses to the County’s structures,
facilities, utilities, and population. Existing and future mitigation efforts should continue to be developed
and employed that will enable the study area to be prepared for these events when they occur. The overall
hazard ranking determined by the Planning Committee for this hazard is high (see Table 5.3-6).

        DMA 2000 Hazard Mitigation Plan – Suffolk County, New York                                   5.4.3-21
        October 2008

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