ML17341A293
| ML17341A293 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie, Turkey Point  |
| Issue date: | 12/20/1974 |
| From: | Brooks E, Gerrish H, Hiser H, Senn H BOSTON COLLEGE, CHESTNUT HILL, MA, MIAMI, UNIV. OF, CORAL GABLES, FL |
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| NUDOCS 8107060185 | |
| Download: ML17341A293 (72) | |
Text
Ci APPENDIX 2C A COMPARATIVE STUDY OF FLORIDA'S MOST SEVERE TORNADOES WITH THOSE IN OTHER PARTS OF THE CONTINENTALU. S.
Dr.
Edward M. Brooks, Professor, Department of Geology and Geophysics Boston College, Chestnut Hill, Massachusetts Harold P. Gerrish, Assistant Professor, Homer W. Hiser, Professor, and Harry V. Senn, Associate Professor, Institute of Marine and Atmospheric Sciences, University of Miami, Coral Gables, Florida DOCKET NO. 50-335:
FLORIDA POWER & LIGHT COMPANY MIAMI, FLORIDA 0
I 8107050185 810505
'DR ADOCK 05000250 G
36 - 12/20/74
I
TABLE OF CONTENTS 2.0 DETERMINATION OF TORNADO WINDSPEEDS 2.1 Direct Measurements of Wind Speeds 2.2 Indirect Measurements of Wind Speeds 2.2.1 Determining the windspeed from its dynamic pressure 2.2.2 Determining the windspeed from its static pressure 2.2.3 Synoptic factors affecting storm intensity and windspeed 2.2.4 Devastation statistics and their relation to windspeed Y
3e 0 CONTINENTAL U ~ S ~
TORNADOES e'.1 The Minneapolis Minn., Tornadoes of 20 July 1951 and 20 August 1904 3.2 The Brandon Ohio Tornado'f 20 January 1954 3.3 The St. Louis, Mo., Tornado of 27 May 1896. and Washington, Kan.
Tornado of 4 July 1932 3.4 The Wallingford, Conn.,
Tornado of 9 August 1878 3.5 The Minneapolis, Minn. Tornado of 20 August 1904; Harrison, Ohio Tornado of 14 February 1854; Worcester, Mass.
Tornado of 9 June
- 1953, and Tri-State Tornado of 18 March 1925 FLORIDA TORNADOES 4.1 The Hialeah Tornado of 5 April 1925 4.2 The Miami Tornado of 17 June 1959 4.3 The Central Florida Tornado of 4 April 19&6
,0 COMPARISON OF 3 MAXIMALFLORIDA TORNADOES WITH SEVERE CONTINENTAL U.S.
TORNADOES
6.0 CONCLUSION
S
7.0 REFERENCES
'Rev.
36 - 12/20/74
A COMPARATIVE STUDY OF FLORIDA'S MOST SEVERE TORNADOES WITH THOSE IN OTHER PARTS OF THE CONTINENTAL U.S.
1.0 INTRODUCTION
has been evident for some time that Florida tornadoes are consid-erably less intense than the AEC model which was obviously derived from those which have occurred in other parts of the continental U.S.
The pur-pose of this report is to document Florida's most severe tornadoes and to compare these as quantitatively as possible with ma)or tornadoes in other parts of the continental U.S. in order to show that the current AEC model is excessive for Florida.
While thousands of continental tornadoes have been observed in the past, quantitative data on maximum wind speeds and central pressures within the central vortex are practically non-existant.
Doppler radar can provide direct measurements of wind speeds along a radial from the radar location; but only a few measurements have been made during the past 10 years due to the lack of an organized doppler network in the tornado areas.
For a few of the intense continental tornadoes, it is possible to derive windspeeds indirectly from their dynamic pressures on structures that failed and/or from static barometric pressure observations inside or near the fun-nel',
as has been suggested by Brooks~I~ in a comprehensive survey article.
Because of the uncertainties involved in these derivations, the numerical results cannot be taken too li erally.
Unfortunately, static pressure data do not exist for Florida tornadoes and limited data are available for wind computations based upon dynamic pressure.
The relative'everity of tornadoes may also be determined by use of other methods.
One such method is the analysis of the micro-and mesoscale synoptic conditions known to be necessary for severe tornadoes.
Another is the use of statistics on deaths, damage
- produced, etc.
The procedure will be to develop the severity of continental U.S.
and Florida storms and to compare the maximum wind speeds which might be ex-pected in them.
2C-3 Rev.
36 12/20/74
2.0 DETERMINATION OF TORNADO MINDSPEEDS
- 2. 1 Direct Measurements of Mind S eeds Observations by wind instruments'urnish the most accurate measurements; but unfortunately are limited to minor tornadoes or to the outer, portions of major tornadoes.
Inside severe tornadoes, the equipment is destroyed before the maximum wind at that point is reached.
Remote sensing by the use of Doppler radar has probably provided the only reliable measurements to date of the particle speeds in the core boundary regions.(2) 2.2 Indirect Measurements of Mind S eeds 2.2.1 Determinin the s
eed of the wind from its d namic ressure 1/2 mv a
Fd 2
m mass of air t
v ~ speed of wind Let the ob)ect of cross sectional area A sweep out a volume V (equal to Ad) as it is replaced by the same air volume V (equal to
)
(where p ~ air density):
Divide (1) by the equivalents of V:
1/2 pv 2 F
A (2) v
(
)
2F 1/2 pA (3)
This windspeed value applies only to the place and time of the damage and may fall short of the maximum windspeed of the tornado.
and For winds strong enough to produce
- damage, a minimum dynamic pressure of the wind can be found.
It is equal to the computed pres-sure necessary to produce some particular damage.
Engineering estimates can be made of the force required to produce the observed displacement or deformation of selected ob5ects of known mass or internal strength.
Let the kinetic energy of the wind (1/2 mv ) be used to do the 2
work (Fd) of moving an object a distance of d:
2.2.2 Determinin the winds eed from its static ressure From the lowest reading of a barometer, the pressure drop be-low the ambient pressure outside the tornado is computed.
It is as" sumed that the kinetic energy of the wind is derived from the work done on the air as it moves from the ambient pressure to the minimum pressure in accordance with a simplified Bernoulli equation.
How-ever, it is assumed that half of this energy will be lost due to the friction between~
i~o ~ceo)erati.ng air and its more stagnant environment.
The work of the pressure gradient force (F) is:
2C-4 Rev.
36 12/20/74
Fd
~ (A hp) d ~ (hd) hp
~ Yhp distance over which the pressure drop hp is measured cross-sectional area on which the force is acting Y ~ volume of air moved the distance d
Equating the kinetic energy per unit volume (left side of eq.
(2) ) to one half the work per unit volume gives:
1/2 p.
- 1/2
(~Y ).
and
(~h) 1/2 p
(4) 4 In eq.
(4), hp is the, pressure
- drop, measured from an assumed ambient pressure of 30 inches of mercury, at which v is chosen as zero, be-cause the ambient winds are negligible compared to the winds within a tornado.
Since the ambient temperature is about 25'C (77'F), the corresponding ambient air density is equal to 1.19xl0 3gm cm 3.
For the assugption of incompressible air, a constant ambient density of 1.19x10 gm cm is substituted for p in eq. (4).
For the assumption of compr~ sible air, p is assumed to decrease dry adiabatically as the pressure decreases.
The assumption of incom-pressibility is sufficiently accurate for comparisons of wind pres-sure for winds of less than 120 mph.
At higher speeds the larger values of windspeeds for the compressible cases (with lover densities),
may be closer to the true windspeeds than the values for the incom-pressible cases.
In the absence of a barometer
- reading, the static pressure drop can be equated to the vertical pressure drop outside the tornado from the heiIIht of the base of the funnel cloud to the base of the low clouds.
) It is assumed that the mixing ratio (or specific
(
humidity) is spatially invariant, such that the lower edge of the funnel and the low cloud base constitute an isobaric surface with a pressure equal to the condensation pressure.
The method of wind determinations from the minimum static pressure is the least reliable of the three methods, because of un-certainties in the applicability of the simplified Bernoulli equation and in the allowance for loss of kinetic energy.
2.2.3 S no tic Factors Affectin Storm Intensit and Minds eed Over the years have been found to be storms and tornadoes.
involved separating a
certain combinations of synoptic parameters associated with the most vigorous thunder-Generally a subsidence type inversion is low-level moisture tongue from dryer air above.
2C-5 36 12/20/74
'4 Cl
A narrow band of relatively strong wind flow (jet) is required at all levels and it is extremely desirable for the middle-level and low-level jets to intersect.
The optimum height of the wet-bulb temperature of zero degrees is about 8,000 ft.
The storms do not develop spontan-eously but need some sort of lifting mechanism.
A detailed survey by Miller (4) of the specific parameters that play a major role in the production of severe thunderstorms and tornadoes is reproduced in'able 1.
This table was compiled from a computer study of 328 tor-nado cases.
Here an attempt was made to define limits on each par-ameter as required to produce storms of various intensities, and to order the parameters according to importance.
Aside from the above
- comments, there are several other para-meters that must be considered in order to complete the picture.
Rates of change of surface temperature, pressure and dew point provide in-formation on regions of decreasing stability and areas where low-level convergence, vertical acceleration and divergence aloft are occurring most rapidly.
Difluence at 500 mb and 200 mb not only provides a
mass evacuation mechanism aloft but signifies the presence of an ap-proaching positive-vorticity center.
Experience has shown that the "level of free convection" should occur at a higher pressure than 600 mb.
Of the parameters discussed
- above, the following are considered to be the most vital for the development of tornadic storms:
a)
Middle and upper level jets with shear zones b)
Low level jet c) 850 mb maximum temperature field d) 700 mb dry intrusion e)
Low Sfc pressure f)
High Sfc dew points The ultimate intensity, therefore is related to the degree to which each of these parameters approaches the critical limits shown in Table l. If all exceed the specified limits, then one would expect a more severe tornado than if only one-half or more of them did.
"Tornadoes can and do form in the absence of a jet stream, for instance.
- However, these are not as severe as those that form in conjunction with a jet stream.
In South and Central Florida, the limits required for the jets and the dry-air intrusion at the same time are not reached because of the moderating influences of the ~ater on all three sides of the peninsula.
By definition, the most intense tornado produces the highest vortex windspeeds.
2.2.4 Devastation Statistics and Their Relationshi to Winds eeds Quite obviously the number of deaths and amounts of damage pro-duced by various storms can provide an indirect measure of the severity of the storms in terms of windspeed if information on. the population 2C-6 Rev.
36 12/20/74
densities and construction in the paths are available.
Then one can compare those statistics with the rare windspeed observations of a direct nature, or calculated values using indirect methods, and there-by establish a basis for estimating winds of other storms which oc-curred during a given historical period.
However, it is extremely difficult to compare the number of deaths or amount of damage caused by a single storm from an earlier period to a recent one because of the problems encountered in normal-izing the statistics.
It would not be too difficult to normalize population statistics for various years in a given city or state; but the death statistics would still not be valid because of other com-plicating factors which are far more'-'difficult to assess.
For in-
- stance, even in 1896, St. Louis was well populated so that if a tornado hit the same sections
- today, one might expect only a few more deaths from population increases since 'then; but one would ex-pect fewer deaths after considering the factors of (probably) better.
warning services and stronger shelter which is not as easily damaged today.
'The sum total mi.ght be fewer deaths from an equal storm today.
Despite better buildinfj practices, total damages to property would almost certainly be much higher due to the increased value of con-struction in terms of sophistication, the much greater value due to the shrunken dollar, and the greater number of buildings which might
', fall in the same path.
It is clear that we should expect roughly the same number of
'deaths but far greater dollar damage from storms in later years which are actually equal in intensity to their forerunners.
The many com-
'plicating factors in comparing the statistics of various storms in-dicate that one must not assign too much weight to small differences in the number of deaths or dollars of damages in assessing the storms'ntensities or windspeeds.
If, on the other hand, the differences in deaths or damages are an order of magnitude or more, one can be reason-ably certain the storms are of significantly different intensities and therefore windspeeds.
ZC-7 I
Rev.
36 12/20/74
TABLE 1 KEY PARAMETERS IN THE PRODUCTION OF SEVERE THUNDERSTORMS AND TORNADOES (af ter Miller )
4 RANK PARAMETER MODERATE STRONG 500 mb Vorticity Stabilit Lifted Index Neutral or Negative Contours Cross Vort.
Contours Cross Vort Advection Pattern
+30 't more than 30
-3 to -5 Middle Speed Level Jet Shear Upper Speed Level Jet Shear Low-Level Jet Speed Low-Level Moisture Mixing Ratio 850-mb Max-Temp Field 35 knots 15/90 nm 55 knots 15/90 nm 20 knot's, 8
gm H20/kg dry air E of Moist Ridge 35-50 knots 15-30/90 nm 55 to 85 knots 15-30/90 nm 25-34 knots 8 to 12 gm H20/kg dry air Over Moist Ridge 50 knots 30/90 nm 85 knots 30/90 nm 35 knots 12 gm H20/kg dry air W of Moist Ridge 8
Winds Cross 700-mb No-Change Line of Advective Temp.
20'0 to 40'0'0 700-mb Dry-Air Intrusion 12-hr Sfc Pressure Falls Not Available - or Available but weak Wind Field Zero mb Winds from Dry to Moist Intrude at an Angle of 10 to 40're at least 15 knots 1 to 5 mb Winds Intrude at an Angle of 40'nd are at least 25 kn, '.
12 500-mb Height Change Height of Wet-Bulb-Zero above Sfc 30 m
Above 11000 ft.
Below 5000 ft.
30 to 60m 9000 to 11000 ft.
5000 to 7000 ft.
60 Tt 7000 to 9000 ft.
Sfc Pressure over Threat Area 1010 mb 1010 to 1005 mb 100m mb Sf c Dew Point 55'F 55'o 64'F 65 F
nrr.:
nautical miles fc:
surface m:
meters mb:
millibars 2C-8 Rev.
3& - 12/20/74
0
3.0 CONTINENTAL U.S.
TORNADOES Table 2 lists nine tornadoes
~ of which four are tornadoes of maximum intensity (those with speeds above 321 mph) ~
They are arranged in order of their approximate windspeeds
~ b0t since these values are crude, they are grouped according to their central pressure drop in the nearest number of inches of mercury.
Within each group, the differences between the listed windspeeds of two or more tornadoes are of no significance.
Note that "maximum intensity" refers to the rank according to computed wind-speeds.
Note also, that the nine storms listed were chosen simply on the basis that certain data were available for them; not because they were all among the nine most intense of the past 115 years.
Other storms such as the palm Sunday tornadoes in 1965; the Waco, Texas tornado in 1953; the Dallas storm in 1957; the Tupelo, Miss. storm in 1936 and other tornadoes could have been cited as examples.
- However, the last two storms in Table 2
stand out with regard to the number of deaths and the amount of damage produced.
The last, the Tri-state tornado of 1925 was quite obviously the most intense from all standpoints.
4
- 3. 1 The Minnea olis Minnesota Tornadoes of 20 Jul 1951 and 20 Au us t 1904 In the outer portion of the first tornado (Minneapolis Airport, July 20, 1951) a minimum sea level pressure of 29.15" Hg.
was recorded.
It is cited as a verification of the third method.
Even with half the kinetic energy
- dropped, the theoretical windspeed for the compressible case (ill miles/hour) still exceeds the observed fastest mile (92 miles/hour).
The agreement is good enough to warrant the use of the third method to obtain approximate windspeeds.
Even better agreement ig found ip the outer part of the other Minneapolis tornado listed (Aug. 20, 1904) f >, in which the pressure drop at the Cfty Office of the Weap er Bureau was the same.
The wind reached an extreme of 110 milesfhour,t 1 almost identical to the theoretical value.
3.2 The Brandon Ohio Tornado of 20 Januar 1954 The 28 tornado (Brandon, Ohio, January 20, 1854) shows good agree-ff (7) ment'etween
~inds of 164 and 173 miles/hour from static and Hynamic pres-sures respectively.
The lowest static pressure was 28.21" Hg., whereas the dynam$ q pressure was that required to account for the breaking of an oak tree.<i) 3.3 The St. Louis Tornado of 27 Ma 1896 and Washin ton Kansas Tornado of 4 Jul 1932 In the 27" group of tornadoes, the static pressure in the St.
Louis tornado o
May 27, 1896 was measured by an aneroid barometer in Lafayette Park.
When corrected to sea level, it yielded a value of 8) 27.30" Hg.
In the Washington, Kansas tornado of July 4, 1932, the dynamic pressure which bent the top of a railroad signal was found to be 110 lbs/ft (The coefficient of 1.6 the same as for tall buildings, was used to cal-culate the windspeed.)
~ Rev.
36 12/20/74
3.4 The Wallin ford Connecticut Tornado of 9 Au ust 1&78 The Wallingford, Connecticut tornado of August 9, 1878 falls in the 26" category of tornadoes because of the high wind required to ex-plain a 2
X 2 X 4 ft. cemetary stone blown of! its foundation.
3' The Minnea olis Tornado of 20 Au ust 1904 Harrison Ohio Tornado of 14 Februar 1854'orcester Massachusetts Tornado of 9 June 1953 and Tri-State Tornado of 18 March 1925 The four most severe tornadoes belong in the categories of 24" to 22" Hg. mercury.
In the Minneapol s tornado of August 20, 1904, a bar-ometer reading of 23" was obtained.(
If this was station pressure, the tornado belongs in the 24" category.(since the sea level pressure would be nearly one inch higher).
If the barometer had been set for sea level pres-
- sure, then, of course, the tornado belongs in the 23" category'.
Since this ambiguity was not resolved'he tornado was listed with the appropriate windspeeds (compressible case) in both pressure categories.
The other two 23" tornadoes were so listed because of their wind pressures.
In the Harrison, Ohio tornado of February 14, 1854, a
scantling was driven 3 1/2 feet into the ground.(11~
The wind in the Worcester, Mass.
tornado of June 9,
1953 was obtained from the known load resistance on destroyed towers carrying high voltage lines.(>>)
The Worcester tornado was the strongest New England tornado on record.
This tornado formed in conjunction with a ore-cold-frontal souall line that extended from southern Maine to eastern Connecticut on the afternoon of June 9
1953.
The cold front at that time was gently curving from western Maine through western Massachusetts to central Pennsylvania.
Earlier it had assed through the Great Lakes area with widespread tornadic activity in dvance of the front.
The rhythm was such that on the 7th - 9th violent fternoon activity quickly followed relatively quiescent morning situations.
The regeneration of tornadoes on the 9th in the New England area was more pronounced than earlier in the history of the system.
Of the several that
- formed, the one in and around Worcester was tge post severe.
It killed 90 people and produced
$52 million of damage.
<14~
The synoptic environment aloft was highlighted by a jet stream at high levels and warm air advection ahead of the squall line at low levels.
Slight cooling was evident at middle levels.
There waz positive vorticity advection aloft in association with the closed-low in southeastern Canada.
- Hence, mast if not all of the synoptic requisites for a severe tornado were present.
One can only make inferences regarding synoptic situations aloft for the other storms listed in Table 2 because routine data above the surface were not generally available during those years.
The only tornado reaching the 22" category was the Tri-state
The best data for determining the wind pressure are from a steel water tank and adjacent concrete chimney of Orient Mine No.
2 at West Frankfort, Illinois.
The wind pressure was calculated to be 250 lbs/ft or nearly 1/8 of an atmosphere.
The Tri-State tornado oT 1925 had a path length of 219 mi, a width of 1,000 to 2,000 yds and traversed predominantly rural areas at a speed of 57 to 68 mph.
Had it hit more populous areas both the number of deaths and the damage would have soared even higher for
'most intense storm observed in over a century.
2C-10 Rcv.
36 12/20/74
y TABLE 2 APPROXIMATE WINDSPEEDS OF CONTINENTAL U ~ S.
TORNADOES (hp) 30-(P)
/Inches HG (P)
Central P
of Tornado Inches HG Windspeed (miles/hour)
Determined Theoretical (Static)
(Refer to Incom ressible Com ressible Ke Place 6
Damage Date Reference Deaths Me ad liars) 29 28 119 169 121 174 92m, ills (Outer Portion) 164s l 173d '"
1/20/
1854 Brandon,(7)
Ohio 7/20/
Minneapojiq, 1951 Minn.
No Data "Heavy" nIll 27 26 206 238 214 251 2036 210d 260d 5,12 /
.'96
~ I I I I 4 l '~32 8 tq/
1678 St. Louis rro.
Wa shing ton (9J Wallingford, Conn.(~0) 3v6 30 12.9
.25 W
M Cl
'4 5
25 24
.'.67 292 23 316 22 337 Key to windspeed determinations:
v means observed vindspeeds.
285 316 348 377 321s 340d 348s 343d 363d e/20/
1904 2/14/
1854 8/20/
1904 6/9/
1953 3/18/
1925 Minneapolis Minn.
Harris~~~
Ohio Minn. (6)
Minn.
Worcester Mass.(12 Murphysboro, Ill.(Tri-State) 14 No Data 14
'0 1.5 No Data 1.5 52.0 165 Note:
All dynamic 6 observed windspeeds include the effect of translation; statrc Mind-speeds do not, d means calculated from dynamic pressure of Mind producing structural failure.
llllIlls ra l cur a ted from observed stat ic pressure drop from ambient to tornado center
4.0 THE FLORIDA TORNADO Lists of all knovn tornadoes in Florida east of the hppa-achicola River (excluding the panhandle region) have been compiled.
ne list includes 114 storms from 1887 to 1949 taken mostly from Flora's Tornadoes of the U.S.(
), and Monthly @cather Reviews(
)'. The other includes 315 storms from 1950 to 1968 inclusive, all from the Storm Data and Unusual Weather Phenomeqa" from the National Summar of Cl imatolo ical Data.
Dept.
Of Co~erce.(17'sing all known data on each storm including deaths,
- injuries, damage
- produced, path length and width, speed of motion, and type of area af fected, each of the tornadoes was graded on an intensity-scale which included 1
(minimal),
2 (moderate),
and 3 (maximal) categories for Florida tornadoes.
The results are shown in Table 3 below.
TABLE 3 INTENSITY RATINGS OF 429 FLORIDA TORNADOES 1887-1949 1950-1968 Minimal Moderate 89 20 273 36 Maximal The two lists were kept separate because of the obvious population and porting differences vhich existed during the tvo periods.
One vould pect that many minimal storms would have been unreported during the early period; whereas in the later years every water~pout, "waterspout-tornado",
"whirlwind", etc.,
had found its vay firmly into the permanent statistics.
The average tornado in Florida is of minimal intensity, barely able to unroof relatively old wooden farm buildings, packing houses and garages, and/or to defoliate, defruit or blov down trees.
The "moderate" category vas generally reserved for storms which "demolished" or "destroyed" at least one or two normally constructed, wood or stronger buildings, possibly caused personal injuries to a number of people and/or had significant path widths or damage estimates.
The maximal category either did significantly greater damage over a larger area, or it appeared from other facts that it would have had it occurred over a suitable area.
To assume the most con-servative attitude, the three most intense tornadoes in Florida history (82 years) vere chosen for comparison with the AEC standard
- tornado, as probably embodied in the most intense fram Table 2, Section 3 above.
The three Florida storms occurred on April 5, 1925, June 17, 1959, and April 4, 1966.
No direct measurement of vindspeed has been made in a Florida tornado.
Indirect calculations have not been presented herein because speeds on the order of 150 to 200 mph could have prpduced all the damag'e that has been photographed and tabulated for Florida tornadoes.
Attempts are still in progress to locate evidence of speeds higher than this, hovever, all efforts to date have been unsuccessful.
The fact that the 2C-12 Rev.
36 12/20/74
three nost severe tornadoes in Florida occurred in or near populous areas prohibits much higher speeds or they certainly would have been documented by the damage.
4.1 The Hialeah Tornado of A ril 5 1925 This storm developed early in the afternoon in advance of a cold front that was pushing down the state from a wave-cyclone centered near Jackson-ville, Florida.
At the time of the tornado, the front extended off the south-west coast near Ft. Myers, Florida.
The tornado developed prior to 1:15 P.M.
and its motion was toward the northeast et approximately 12 mph.
After 20 minutes of progressive movement the tornado stopped and remained stationary for 5 minutes.
During this period it rose and descended t~ice. It then resumed its northeastward motion causing more damage.
The total damage was estimated at
$.25 million and there were five deaths.
Its diameter in-creased greatly as it passed north of Miami and became obliterated by heavy rain soon afterward.
No serious damage was done after that time.
The tornado was preceded by a heavy fall of hail which was confined primarily along the path; and in some areas the ground was completely covered with hailstones as large as a baseball.
The path of the tornado itself was 12 miles long and slightly less than 100 yards wide.
Upper-air sounding techniques of today were not available in the twenties.
As a result, the upper-air structure is not known with any degree of certainty.
Since the tornado moved rather slowly, it can be inferred that the steering current was weak and that no divergence or mass evacuation mechanism such as a jet stream existed aloft.
4.2 The Miami Tornado of June 17 1959 While all eyes were on Tropical Storm Beulah, centered 100 miles north-east of Tampico, Mexico, a tropical depression formed rather unexpectedly in the eastern Gulf near 25.5'N, 86.5'W on the afternoon of June 17, 1959.
During the night it deepened and moved northeastward at 35 mph crossing the west coast of Florida.just south of Tampa and exiting the east coast just north of Cape Kennedy.
The tornado occurred in Miami at 9:50 P.M. on the 17th.
This position was in the right front quadrant approximately 230 n. miles from the center of the deepening depression.
Hiser (18) has summarized the eye-witness accounts of the tornado as it moved from the Coconut Grove area of southern Miami skipping over populous areas near downtown Miami, thence down to the ground again in North Miami.
The total damage was estimated to be
$ 3 'million and no lives were lost.
The state climatologist described the storm as the most intense since the 1925 storm.
Despite the improved south Florida building codes, neither the total damage nor the loss of life reached the potential that an intense midwestern storm should have produced over such a
populated area.
Although there was no major jet stream over South Florida during this
- period, there may have been a narrow zone or finger of relatively higher wind speeds on the order of 50 knots from Miami to Grand Bahama.
Miami reported a wind at 18,000 ft. of 220'/5l knots.
At Grand Bahama the ~inds 2C-13 Rev.
36 12/20/74
above 40,000 ft. were 50 knots or greater.
This may have provided some degree of mass evacuation aloft.
The tornado moved toward the north-east at 25-28 miles per hour
).
The Lifted Index was -3.7.
The wet-(18 temperature of zero degrees was at l3,000 ft. above M.S.L.
A frontal system moved down the state on the 2nd of April and stagnated in South Florida on the 3rd.
During the night of the 3rd it washed out and another system moved into the Southeast U. S. trailing a front along the Gulf Coast.
The second frontal system moved into the Gulf on the 4th passing through central Florida that night and off the southeast coast during the afternoon of the 5th.
Several stable waves formed on that front during its history.
During the morning of the 4th, a tornado formed near Clearwater, Florida and moved east-northeastward across the state to Gibsonia and thence to the Merritt Island area.
Another tornado or a family of tornadoes began at Pinellas Point and passed through southern sections of Lakeland, Haines City and thence to Rockledge on a track parallel to the above.
Evidence indicates that the northernmost storm maintained continuous contact wirh the ground from the Gulf to the Atlantic ocean, a distance of 140 miles, The southernmost storm produced an intermittent track as if one tornado lifted and lowered or possibly a family of tornadoes were involved.
The
- northern one was the most severe and produced the most damage of the two.
Eleven people were killed, 400 were injured, and property damage was estimated at
$ 11 million.
Quite obviously, this was a major storm, probably the largest of Florida record; although no photographs of the funnel(s) have been found because they may have been obscured by precipita-tion.
Considering the nature
~x this storm and the populated areas traversed by it, it is relatively certain thai one damage and deaths were not nearly as great as might have been produced by winds of the order of 300 mph.
This outbreak was associated with a sq.i . line in advance of the frontal system which was located near New Orleans at that time.
There was strong convergence aloft at 5,000 ft. with a high-level jet finger of 85 knots oriented WSW-ENE over Tampa.
The main jet was over the southeast r
ou eastern
.S.
A speed maximum on the order of 60 knots was evident at mid-levels down to at least 10,000 ft.
This arrangement of speed maxima aloft is conducive to severe tornadoes, see Table 1.
However,- there was no indication of strong vorticity advection at 500mb which normally accompanies severe storms.
The wet-bulb temperature of zero degrees in this storm was at 13,000 ft. (the same as the
'59 tornado),
and the Lifted Index on the basis of a partial sounding appeared to be positive.
Proximity soundings showed that while there was a tendency for some drying above 750mb in the 1959 storm, both it and the 1966 tornado sound-ings were quite moist resembling the Type II Gulf Coast soundings of Fawbush and Miller.
Miller states that the Type I sounding is the optimum (4) for severe tornadoes.
None of the most severe tornadoes observed in peninsular Florida had Type I air-mass structures.
This and certain other ey ingredients such as requisite jet maxima, vorticity advection and dr air intrusion h vc always been missing in varying degrees from even the most severe Florida tornadoes of record.
2C-14 Rev.
36 - l2/20/74
'I
5.0 COMPARISON OF THE THREE MAXIMALFLORIDA TORNADOES WITH SEVERE CONTINENTAL U. S.
TORNADOES Flora reports 192 tornadoes in Florida during the years 1916-1949.
(14)
During this same period, Illinois experienced 190 tornadoes.
- Hovever, Florida's losses amounted to 31 deaths and 2.4 million dollars property damage while the Illinois losses vere 917 deaths and
$53.8 million in property damage.
The tvo states are of approximately equal area.
The population density per square mile in Illinois vas about five times that of Florida.
But the Illinois deaths were 30 times larger and damage was more than 22 times greater than Florida's.
Flora also listed the outstanding U ~
S.
tornadoes of this period.
Several Illinois tornadoes were listed but none for Florida.
All of this indicates much less severe tornadoes in Florida than in the midwestern state of Illinois.
Between 1916 and 1958, the average number of people killed per tornado was about nine times higher in the continental U. S.
(1.04) than it was in Florida (. 12) (
In another important'ornado publication, Wolford lists the outstand-ing tornadoes from 1876-'1958 for the entire U. S. (13) Again, no Florida storms vere included in her lfstfng of 172.
Tvo measures of the fntensfty of tornadoes used by Wolford include deaths and monetary damage values.
Figure 5.1, giving the number of deaths caused by the outstanding storms fn Continental U. S.,
shows clearly that those caused by Florida's most severe would rank her storms in the lowest category of the U. S. outstanding storms.
Figure 5.2, sho~ing the damage
- produced, also tends to confirm the the Florida tornado is not nearly as intense as the most severe storms found elsewhere.
Insofar as tornado intensities and thus windspeeds can be inferred from deaths and damage statistics, it can be shown that continental U. S. storms have considerably higher winds than Florida storms.
Evidence presented above shows that there is a greater than order-of-magnitude difference in the statistics for all three of Florida's most severe storms when compared to the most intense of the other continental U. S. tornadoes.
Since,all three of the severe Florida storms passed over populated areas, in recent years, they had ample opportunity to significantly'aise the statistics.
The only logical conclusion fs that they vere not nearly so intense as the most severe continental U. S.
tornadoes.
The synoptic environment associated with the three Florida tornadoes was such that several of the key parameters which are generally" accepted as being necessary for severe tornadoes, see Section 2.23, were missing.
The relatively slow movement of the April 5, 1925 and June 17, 1959 storms indicate that no significant synoptic-scale jet stream existed aloft fn those cases.
The fast-moving April 4, 1966 tornado did have appropriate wind speeds aloft but they were assocaited with a finger or branch of the main jet vhich was located in the southeastern United States.
Because of the moderating effect of the marine environment around and over peninsular Florida, the dry-air intrusion requirements vere not met.
Therefore, insta-bility conditions associated vith intense storms did not develop.
In addition, positive vorticity advection was not indicated in the April 4, 1966 or June 17, 1959 tornadoes.
Upper-air charts vere not available for the April 5, 1925 storm.
2C-15 Rev.
36 12/20/74
fthe five most severe continental tornadoes for which wind speeds could be determined, Table 2, only one was recent enough to permit both
.-. upper-air and surface synoptic analysis.
This Worcester, Mass.,
tornado of June 9,
1953 had the ingredients expected for severe storms as set forth in ble I after Hiller.
The only reliable direct measurement of windspeed in a tornado was 206 mph in the June 10, 1958 storm at El Dorado, Kansas.
This was recorded using Doppler radar.
There ha've been no higher measurements since then.
On the basis of indirect measurement, it must be concluded that the most intense continental tornadoes are capable of producing windspeeds on the order of 360 mph which includes effects of translation.
The windspeeds cal-culated upon the basis of static pressures are not as reliable as those cal-culated from dynamic pressures.
The resulting overestimates in the static pressure calculat'ions approximately equal the translation speeds which are included in the dynamic computation.
The static value of 377 mph in Table 2
is for a hypothetical 22 inch tornado.
From the standpoint of damage, photographs in Florida do not show build-ings being swept clean to the ground and debris carried away as in the most severe continental tornadoes.
In no, case did the damage substantiate wind speeds exceeding 165 to 200 mph.
e 2C-16 Rev.
36 12/20/74
I
I ~
ci
~t Three greatest Florida storms deaths indicated on abscissa, 0,
5 and ll.
No florida storms included by Qolford.
~
~
.}
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~
tt ~
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~
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t tt ~
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~ 0
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rtl
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~ t
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ttrt
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FLORIDA POWER C LIGHT COMPANY HUTCHINSON ISLAND PLANT DEATHS FROM "OUTSTANDING" TORNADOES Of THE U. S.
1876-1958 (Wolford
)
FIG. 5-1 2C-17 Rev.
36 12/20/74
~ ~
~ +
~ 1&
I ~
~ ~
(l.l
~
I
~ I
~ fll I~
f
~
- 'hree greatest Florida storms property damage indicated on
~
- abscissa,
~ 25, 3 and 5 ~
No Florida storms included by Wolford.
~ )
~
~ ~
~ I
~ ~ l
~I
~
~
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~
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~
~
~%~
I ~
~
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~ ~ ~
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~ II
~
~ ~
.) '.
~ ~
~ ~
~ lI ~
f
~ ~ +
~ L4
~
~ I
~ ~
T: ~
~ l
~ e
~
I
~
~
i'P f4 P
~sf r'4
~
J
~W J ~
~ II ~r"
~rt
~ f.
~ ".
I ~
JIB
~ I
~ 4t
~
~~
~
~
~f FLORIDA POWER 6 LIGHT COMPhNY HUTCHINSON ISLAND PLANT DAMAGE FROM "OUTSTANDING" TORNADOES OP THE U. S.
1876-1958 (Molford
)
FIGHT 5-2 2C-18 36 12/20/74
0
6.0 CONCLUSION
S It has been shown by calculations from dynamic pressures that the most severe U. S.
tornado in the past 115 years had a maximum vindspeed of 363 mph which included a translation speed of about 60 mph.
Unfortunately, limited observations or calculations were possible for Florida's most intense storms.
On the basis of deaths or injuries, and property damage suffered, the most severe tornadoes in Florida history produced less severe effects by a full order of magnitude than the most severe storms which occur in other parts of the continental U. S.
No photographs or records of damage have been found to substantiate speeds exceeding approximately 200 mph in Florida tornadoes.
In addition, other key ingredients for severe tornadoes such as air-mass structure, jet maxima, vorticity advection, and dry air intrusion, have always been missing in varying degrees in Florida tornadoes.
This is a result of Florida's southern latitude and its marine environment.
While it may be possible to produce wind speeds greater than 200 mph (including translation effects) in Florida tornadoes, it is highly unlikely that they should ever reach.300 mph.
This upper limit is postulated on the basis that all key synoptic parameters will.never simultaneously exist in peninsular Florida and that the order of magnitude difference in damage statistics indicates that higher wind speeds do not occur.
2C-19 Rev.
36 12/20/74
7.0 REFERENCES
~
~
~
~
~
~
~
~
~
~
~
(2)
Smith, R.L., and D.W. Holmes, 1961 ~ "Use of Doppler Radar in Meteor-ological Observations",
Mon. Wea. Rev., Vol. 89, No. 1, pp 1-'7.
(3)
- Ferrel, W.~ 1893, Po ular Treatise on the Winds, Chapter VII, pp 34 7-350.
(4)
Miller, R.C.,
- 1967, Notes on Anal sis and Severe-Storm Forecastin Procedures of the Militar Weather Warnin
- Center, Tech.
Report No.
USARo AWS ~
(5)
Hovde, M.R., 1952, "The Hennepin County Tornado of July 20, 1951",
Weatherwise, Vol. 5, No.
3, June, pp 60-62.
(6)
Outram, T.S.,
- 1904, "Storm of Aug. 20, 1904, in Minnesota",
Mon. Wea. Rev., August.
(7)
- Stoddard, O.N., "The Tornado at Brandon, Ohio, Jan.
20, 1854",
American Journal of Sciences, Vol. 68, pp 70-79.
(8)
Frankenfield, H.C., 1896, "The Tornado of May 27 at St. Louis, Mo.",
Mo.Wea. Rev., March.
)
Marshall, J.D.,
1932, "Calculations Regarding Tornado Velocities at Washington,
- Kansas, July 4, 1932", Bull. of American Meteor. Soc.,
August.-Sept.,
p 149.
(10)
Haze-,
H.A., 1890, "Facts about Tornadoe ", Science, Vol. 16, August, pp 58-62.
(11)
- Stoddard, O.N., "The Tornado at Harrison, Ohio, Feb.
14, 1854",
American Journal of Science, Vol. 70, No. 161.
(12)
Booker, C.A., 1953, "Tower Damage Provides Key to,Worcester Tornado Data", Electric World, N.Y., Vol. 140, No. 7, pp 22'-24.
(13)
Western Society of Engineers, Committee,
- 1925, "Report on Effects of Tornado of March 18, 1925, also Sugestions in Regard to Design of Structures",
Western Societ of En ineerin
- Journal, Vol. 30, No. 9, September, pp 373-396.
(14)
Wolford, L.V., 1960, Tornado Occurrences in the United States, Tech.
Paper No. 20, U.S.W.B., 7lpp.
(15)
- Flora, Snovden, 1954, Tornadoes of the United States, University of Oklahoma Press, March, 22lpp.
(16)
U.S.W.B., Dept. of Commerce, Monthl Weather Reviews for the period 1871-1949.
U.S.W.B., Dept. of Commerce, "Storm Data and Unusual Weather Phenomena",
National Summar of Climatolo ical Data, 1950-1968.
2C-20 Rev.
36 12/20/74
I
(
j t
(18)
- Hiser, H. g., 1968, "Radar and Synoptic Analysis of the Miami Tornado of June 17, 1959", J.
A
- 1. Meteor.,
Vol ~ 7, No.
pp 892-900.
(19)
- Fawbush, E.J.,
and R.C. Miller, 1954, "The Types of Airmasses in Which North American Tornadoes Form", Bull. Amer. Meteor.
Soc., Vol. 35, No. 4, pp 154-165.
'ev.
36 12/20/74
APPENDIX 2F THE DESIGN BASIS TORNADO FOR THE ATLANTIC COAST AND FLORIDA'S EAST COAST TORNADO DESIGN CRITERIA An analysis of all tornadoes occurring along the Atlantic coast recorded in Storm Data for the period 1950 to 1972 is given in paragraph II.
A Design Tornado was developed in parallel with the methodology presented 1
in "Technical Basis for Interim Regional Tornado Criteria."
Maximum speed 218 mph 2 ~
3.
Tangential wind speed (rotational) =
163 mph Translational wind speed, maximum =
55 mph minimum 5 mph 4.
5.
Pressure drop at center of vortex =
Maximum rate of pressure drop
~ 944 psi F 508 psi/sec II.
BASIS FOR SELECTION OF DESIGN TORNADO The development of a "design tornado" follows the probabilistic approach
-7 1
proposed by the AEC which results in the probable 10 per year wind speed.
-7 In this investigation, the 10 per year Design Tornado is determined for the Atlantic Coastal region.
All tornadoes reported in stoma Data (and confirmed by the N.S.S.F.C.
logs between 1950 and 1972) which occurred within 4 miles of the Atlantic Coast, or within the Florida Keys were included.
2F<<l Rev.
36 - -12/20/74
d u on the in an o 3e b
ctxve guide base p
f 'ensity was made us g
ssification o in e lassi a
e e
III given sufficient ale described in Section I ames S Hoore Intensity Sca e
e Red Cross and news clippings.
e r Storm Data or the American Red Cross detail from either Storm a
inc and a of eac o
ined from path length an a of each tornado was determine Similarly, the area of eac o
width data.
The geometric probabi y
'lit is given by P
=
n (a/A) of a tornado striking a point when P
~
mean n
an annual probability o a
wit the area A per year n
~
mean number o
tom n
~
f adoes occurring wit a
=
average pa th length X path width ed for the Atlantic Coast are as follows:
The values us Atlantic Coast
-7 10 wind speed 0.257 mi2
.2 16,100 mi
-1 9.0 yr "4
-1 1.44 X 10 yr le of tornadoes, the average Since Florida a
h d by far the largest samp e o was used for the Atlantic coast.
(P X P
) found for Florida was use o
tornadic area hi hest o
e f th average areas of all u
of "a" from Florida was the h g The val e ve assumption.
The therefore a conservative a
the Atlantic States and it is t ere a
in is coupled with it of any tornado striking a poin geometric annual probability o any 2F-2
- Rev.
36 12/20/74
~7 the probability of a given intensity to yield the probable 10
{per year) wind speed.
The resulting value for the Atlantic coast is 218 mph.
It is felt that the departure of the intensity frequencies from a log-normal distribution is more than adequately compensated for by using the upper bound of the intensity interval.
Also, it is likely that a bias exists in the reporting of tornado events.
This results primarily in an under-reporting of unseen or less damaging tornadoes which would probably fall into the DGMland DaM 2 categories and reduce the slope of the curves shown in Figure l.
Little recorded data was found on translational wind speed in the regions of interest. Flora, for example, states that 45 mph is the average trans-(2)
(2) lation wind speed based upon a study of 1,000 tornadoes by J.R. Martin and Wolford states that 40 mph is the average for all tornadoes.
A (3) general opinion among severe weather meteorologists is that tornadic in-tensity is correlated (indirectly) with translational speed.
This is due to the fact that intense storms are associated with strong gets in the mid-levels of the troposphere which in turn propels the parent cloud in pro-portion to the average wind speed of the cloud layer This is supported (4) by a study of long track
(> 100 mi. path lengths) tornadoes which are very (5) intense tornadoes and have an average translational speed, of 67.8 mph 2F-3 Rev.
36 12/2p/7q
The Design Basis Tornado parameters are shown below.
Max. Speed
~{m h)
Rotational S eed (m h)
Translational S eed (m h)
Total Pressure Dro (Psi)
Maximum Rate of Pressure Drop
( si/sec)
Max.
Min.
218 163 55
~ 944
.508 The maximum rate of pressure drop occurs at the radius of maximum wind and is determined by:
dt v 2 o
m A rm where p
=
pressure t
=
time T
=
translational speed r
=
radius of maximum rotational windspeed - 150' V
=
maximum tangential wind m
The total pressure
- drop, hp, is determined by:
~3 dr Gr V
2
~p~
m dr r
o the application of the cyclostrophic wind equation.
The maximum value of 218 mph is consistent with the previous studies con-ducted by Florida Power and Light where the maximum tornadic wind is (6) seen from damage estimates to be in the range of 165 to 200 mph 2F-4 Rev.
36 - 12/20/l4.
The Design Tornado for the Atlantic Coast is less than that determined by the AEC for Region 1.
This results from the following:
(1)
The geometric probability is less using the actual path length and width of the region under consideration.
The average area of these tornadoes is an order of magnitude less than Iowa
.2
.2 tornadoes,
.26 mi vs.
2.82 mi (2)
Some of these coastal tornadoes are actually "tornadic water-spouts" or have been induced by hurricanes and are seldom intense due to the lack of strong vertical shear of the hori-zontal wind through a deep layer of the atmosphere.
This shear is essential to the explosive development of large rotating (7i8rg) thunderstorms which spa~n severe tornadoes.
(3)
The D&M Inteisity Scale is based upon extensive analysis of the effects of wind loadings upon structures such that an objective estimate of wind speed may be made from written summaries of damage accounts.
Although a comparative study has yet to be made, it is likely that differences exist between the D&M Intensity classifica-.
tion and the F-Scale classification.
III DAMES
& MOORE INTENSITY SCALE Dames
& Moore tornadic wind intensity scale was created in order to evaluate tornado damage and associated causative wind speeds.
In development of this scale, it was necessary to calculate the range of wind speeds which could 2F-5 Rev.
36 - 12/20/74
conceivably give rise to reported structural damage.
Probable wind velocities were estimated from observed damage and these velocities were used to classify tornadoes according to intensity.
The results of these evaluations permitted a reasonable classification of tornadoes according to wind velocity-damage relationships which are in general agreement with (10) other attempts Several assumptions were necessary in order to evaluate the wind velocities associated with varying damage of residences and other buildings.
Con-struction variances resulting from differences in local codes and workman-ship and quality of construction were accounted for in the calculation of the range of wind velocities associated with particular types and extents of damage.
Due to the extent of these variations, a fairly wide range of over-lapping wind velocities is given for each type of damage.
Specific assumptions were employed regarding the action of wind forces on the building.
A sustained peak wind velocity was considered.
Gusting
- effects, repeated
- loadings, and racking of structural members and joints were not included.
The effects of rapid decrease in air pressure on the structure were disregarded since natural venting through broken windows, damaged siding, etc. minimizes or negates the pressure drop effects and few such cases were observed in the tornado record.
The wind pressure coeffi-cients utilized in the structural calculations were selected from the American National Standard Building Code, 1972. (11)
Various sizes and numbers of connectors were assumed for the roof to wall connections, thus yielding a range of wind velocity values associated with varying roof damage levels.
Calculations were made to verify the wind forces required to inflic 2F-6 Rev.
36 - 12/20/74
these levels of damage, for partial or total roof removal.
The specific results of the above mentioned calculations are reflected in Table I entitled "Dames S Moore Tornado Intensity Classification."
Progressively higher degrees of damage are summarized in the damage description for Dames a Moore Intensity categories l through 6.
Each category has an associated velocity range which is the sum of the rotational and translational speeds.
The major source of damage description was obtained from the N.S.S.F.C.
records and Storm Data.
This information was supplemented by data obtained from the American Red Cross and some newspaper articles.
In classifying the tornadoes, engineering estimates were based predominately on the highest degree of damage occurring in the description.
If the available damage description was inadequate or nonexistent, the tornado path length and width, the dollar damage category and the geographic location were considered in assigning the appropriate damage intensity.
However, in some instances, the information available fram the storm Data or American Red Cross was insufficient for classification in accordance with the Dames 6 Moore Intensity guidelines and, therefore, that tornado was not analyzed.
The application of these guidelines to the Atlantic states is given in Table II.
21'-7 Rev.
36 12/20/74
IV~
FLORIDA EAST COAST ANALYSIS A separate analysis of tornadoes occurring within the four mile d.
All inland coastal strip of the Florida Atlantic Coast is provide reported tornadoes which originated, terminated or crosse d the four mile coastal strip are included in this analysis.
- However, the computed tornado affected areas (path length and width) are only restricted by an upper path limit of 10 miles.
The methodology is identical to the one described in the previous sections except only tornado occurrences indigenous to the Floiida east coast are analyzed.
Table III summarizes the climatological tornado data of the Florida east coast by year of occurrence and county.
During the period 1950 to
- 1960, 34 tornadoes were sighted.
However, during the period 1960 to 1970, 67 tornadoes were sighted.
Comparing the two decades of time, the number of tornado reports increased by 97%.
The population increase for the east coast of Florida (documented in Table IV) from 1950 to 1970 was 183'.
If;;climatological tornado trends are discounL~J, there appears to be a
correlation between increasing tornado reports and increasing population (5) densities.
Intense tornadoes,
- however, normally affect a large area and the tornado sightings should be independent of population density in an already populous region.
Many lov intensity tornadoes may have been undetected or not reported in the earlier portion of the sampling period.
The increase in the tornado-affected area ('a'erm in the geometric probability equation) associated with unreported low intensity tornadoes is small as compared to more intense reported tornado occurrences.
2F-8 Rev.
36 12/20/74
As previously defined:
P = n(g/A) where:
0.257 miles (for Florida East Coast)-
2 2
2420 miles (area examined) n = 112/23 (1950 to 1972)
-4
-1 P ~ 5.17 x 10 yr Table V summarizes the Florida East Coast tornadoes by the Dames s Moore upper class intensity scale.
Figure 2 is derived from the data in Table V.
To determine the extrapolated percent probability with the associated maximum wind speed for the one in ten million probability-
-7
-3 P of 1.0 x 10
=
0.193 x 10
= 0.0394.
P for Florida East Coast
-7 and the associated maximum win-'peed, from Figure 2, is 242 mph for 1.0 x 10 probability level.
Detailed information on the tornadoes under study is provided herein.
Table VI gives the chronological list of tornadoes for the period of 1950-1972 and the available path lengths, widths and areas.
Table VII classifies these tornadoes into the Dames
& Moore intensity categories.
The tornadoes are tabulated according to damage description in each intensity category.
The miscellaneous category includes the damage descriptions listed in Table I which are not separately described in this table.
For purposes of summarizing the Florida East Coast tornado intensity classification, Table VIIIhas been prepared.
It should be pointed out that for tornadoes where the area data is not available the average area was assumed for purposes of this analysis (See note 2, Table VIII).
2F-9 Rev.
36 12/20/74
Technical Basis for Interim Regional Tornado Criteria, WASH-1300 (UC-11) f U.S.A ~ E.C. Office of Regulation, May, 1974.
2 ~
Flora, S.D.,
Tornadoes of the United States, University of Oklahoma
- Press, Norman,
- Oklahoma, pp. 194,
- 1954, 2nd edition 3.
Wolford, L.V., Tornado Occurrences in the U.S.,
USWB Tech Paper No. 20, 1960 Wilson, J.W.,
"Movement and Predictability of Radar Echoes",
ERCTM-NSSL-28,
- Norman, Oklahoma,
- November, 1966 5.
Wilson, J.W.
and Morgan, G.N., "Long-Track Tornadoes and Their Significance",
Preprints.
Seventh Conference on Severe Local Storms, A.M.S., Kansas City, Missouri, October 5-7, 1971 6.
Brooks, E.M., Gerrish, H.P., Hiser, H.W. and Senn, H.V., "A Comparative Study of Florida's Most Severe Tornadoes with Those in other Parts of the Continental U.S.", Docket No. 50-335, Fla.
Power and Light Company, Miami, Florida 7.
- Newton, C.W.,
1950 "Structure and Mechanism of the Prefrontal Squall Line", J. Meteorolog
, Vol. 7, No. 3, pp.
210-222 8.
Ward, Z.B., "Rotational Characteristics of a Tornado Cyclone",
Preprints, Sixth Conference on Severe Local Storms, A.M.E., Chicago, Illinois, October, 1969 9.
Nicholson, F.H.,
"The Formation of Severe Local Storms Through the Agency of Random Turbulent Transport",
~pre rints, Eighth conference on Severe Local Storms, A.M.Ses Denver, Colorado, October 15-17, 1973 10 Fujita, T.T., "Proposed Characterization of Tornadoes and Hurricanes by Area and Intensity", Chicago University, Department of Geophysical
- Sciences, Satellite and Mesometeorology Research project, Research Paper No. 91, February 1971.
"American National Standard Building Code Requirements for Minimum Design Loads in Buildings and Other Structures", eAmerican National Standards Institute, New York, New York, A58.1 - 1972 2F-10 Rev.
36 12/20/74
TABLE I DAMES AND MOORE TORNADO INTENSITY CLASSIFICATION DAMES S
MOORE INTENSITY WIND VELOCITY (mph)
EXPECTED DAMAGE 50"90 Partial roof removal of weak rural structures; some trees uprooted and blown 80-120 Total roof removal of rural structures; partial roof removal of individual residences; house trailers moved or rolled; more extensive tree uprooting 100-150 Rural structures heavily damaged; total roof removal of residences; house trailers destroyed; nonreinforced masonry walls overturned; extensive sign damage and tree uprooting 120-180 Rural structures demolished; total roof removal of residences and some walls down; partial roof removal of light steel industrial buildings and wood truss commercial buildings.
150-225 Complete homes destroyed; total roof remov'al of light industrial buildings and wood truss commercial buildings; partial roof removal of heavy industrial buildings 200-300 Catastrophic destruction; homes off foundations; substantial commercial and industrial buildings destroyed; large steel framed structures heavily damaged.
2F-11 Rc v.
36 12/20/7l(
TABLE II TORNADOES AND THEIR INTENSITIES OCCURRING ALONG THE ATLANTIC COAST FROM 1950 - 1972 Dames S
Moore Intensity FLA.E Class COAST 'A.
SC.
NC.
VA.
MD.
NJ.
MASS.
ME.
Total Classified ByIntensi ty Adjusted Total For All Tornadoes 6
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
3, 31 0
1 3
0 1
0 0
0 0
0 4
11 5
6 6
2 3
3 1
2 7
1 2
2 2
4 7
5 2
1 4
1 26 73 71 15.8 29.2 82.1 79.9 TOTAL 98 All Tors 112 7
18 22 12 11 5
7 4
7 20 25 12 11 6
10
,'4 207 207 2F-12 Rev.
36 - 12/2P/74
~ ~
~~~~~~~~~KR
~~~~~~~~KH WWMRRRRRSMMRR~W M
~~MS~~~~RR
~~~~~~~%%~%%
~~~~~5%~RR
~~~~M%~~~5%~~
TABLE IV POPULATION IN COASTAL FLORIDA COUNTIES U.S.
BUREAU OF CENSUS 1950 1970 Dade Broward Palm Beach Martin St. Lucie Indian River Brevard Volusia Flagler St. John'
~
~
Duval Nassau 495, 084 83,933 114,688.
7,807 20,180 11,872 23, 653 74,229 3,367 24, 998 304,029 12,811 1,267,792 620,100 348,753 28, 035 50,836 35,992 230, 006 169,487 4,454 30, 727 528,865 20,626 Totals 1,176,651 3,335,673 2F-14
'ev.
36 12/20/74
TABLE V COASTAL EAST FLORIDA TORNADOES FROM 1950 TO 1972
'ames Moore Intensity Class Florida East Coast Adjusted Total For All Tornadoes Cumulative Frequency Cumulative Percent 1
m 112 + 1 Times 100 Dames 6
Moore Upper Class v/ind S eed m
?:
0 300 225 31
- 10. 3
- 12. 6 53.7
- 35. 4 112.0 101.7 89.1 35.4 0.88 1O.OO 21.15 68.67 180 150 120 90 Subtotal Unknown Total 98 14 112 112. 0 112. 0 2F-15r Rev.
36 12/20/74
TABLE VI
'ornado Statistics for rhe East Florida Coast
Reference:
Storm Data; NOAA Period of Record 1950 to 1972 Number Year
.'Eonth County Length (Miles)
Width (Yards)
Width (Miles)
Area (Sq. Miles) 1950 March Flagler 1952 February Palm Beach 1952 August Palm Beach 4
1953 April St. Lucie 1953 August St. Lucie 1953 September Brevard 1953 September Dade,.
1954 April Dade 1.5
.17 2.0 1.0 150 15 15 200
.009
.009
.114
.014
.002
.114 10 12
@13 18 20 21
"'3 26 27 28 29 30 1955
)956 195b i.956 1958 1958 l958 1958 l958 1958 1959 1959 1959 1959 i.959 1959 1959 October Allg Us r.
August October'anuary April Apl 1 E.
Apl' i AUgUs t AUgUst April June June June SeptLnber October October Broward Pain Beacii
.'!ar t in Dilue Brevard St I Ji'lhn i'sin BL.acn Pain Beacii i'aln Beach Pa in 8<ac E>
Brevard St. John' Dad e Palm Beach Broward Vo lus ia
,'far r. in 1954 August St. Lucie 1954 September Sr.. Lucie 1954 Seprenber Brevard 1955 April 8 rowa rd 1955 August Pain Beach 90 3.0 75 1.0 100 1.0 70 lo(l'.0) 350 7.0 150
.057
.199
.085
.04()
9
.057 1.99
. 595
. E)40 2Z-16 Rev.
36 12/20/74
TABLE VI (Con't)
Tornado Statistics for the East Florida Coast
Reference:
Storm Data; NOAA Period of Record 1950 to 1972 51 5'l 53 54 55 56 57 58 59 60 61 1964 1964 1964 1964 1964 1964 1964 1965 1965 1965 1966 Number Year 31 1960 32 1960 33 1960 34 1960 35 1961 36 1961 37 1961 38 1961 39 1962 40 1962 41 1962 I
7 1962 43 1963 44 1963 45 1963 1963 I 7 1964 48 1964 49 1964 50 1964 Month Julv July September October March April Mav June July August September November July July August
'.:ovember August August August August October October October October October October October February February March April County Volusia Volusia Palm Beach St. Lucie Nassau Duval Palm Beach St. t.ucie St.
Luc ie St. John' Palm Beach Dade Palm Beach Brevard Volusia Indian River Brevard St.
John' Flagler Volusia Dade Palm Beach Palm Beach Mart in Palm Beach Palm Beach Brevard Broward Broward Palm Beach Brevard Length (Miles) 1.0 5.0 15.0 10(14 0)
Width (Yards) 75 60 350
.034
.170
.199
).99 Width Area (Miles)
(Sq. Milesl 2F-17 Rev.
36 - 12/20/74,
TABLE VI (Cont'd)
Tornado Statistics for. the East Florida Coast
Reference:
Storm Data; NOAA Period of Record 1950 to 1972 Number 62 63 64 65 66 67 68 69 70 71 Year 1966 1966 1966 1966 1966 1967 1967 1967 1967 Month April June June June September February June August August 1967 'eptember County Brevard Dade Dade Indian River Brevard Brocard Palm Beach St. Lucie Brevard Palm Beach 4.0 150 Length h/idth Width Area (Miles)
(Yards)
(Miles)
(Sq. Miles) 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 1968 1968 1968 1968 1968 1968 1968 1968 1968 1968 1968 1968 1968 1968 1968 1968 1968 1969 1969 1969 1969 1970 February February June June June June July August August September October October November November February June August October January Dade Palm Beach Brevard Brevard Brevard Dade Brevard Dade Brevard Palm Beach Volusia Volusia Brevard Dade Palm Beach Brevard Palm Beach Dade Dade Broward Volusia St. Lucie 4.5 0.3 0.1 10.0 5.0 2.0 1.5
.25 8.0 1.0 100 125 800 200 30 125
.057
.009
.071
.114
.017
.071
.257
.001
.142
.029
.136
.017 2F-18
- Rev, 36 12/20/74
TABLE VI (Cont'd)
Tornado Statistics for the East Florida Coast
Reference:
Storm Data; NOAA Period of Record 1950 to 1972 Number 94 96 Year 1970 1970 1970 Month February March March County Brevard Brevard Dade 1.9 333
.189
.359 Length Width Width Area (Miles)
{Yards)
{Miles)
(Sq. Mile 97 98 99 100 101 102 103 104 105 106 107 108 109 110 112 113 114 115 116 1970 1970 1970 1970 1970 1971 1971 1971 1971 1971 1971 1972 1972 1972 1972 1972 1972 1972 1972 1972 March July July July February June June August August September February March Harch March June June June June July Palm Beach Hartin Nassau Volusia Palm Beach Palm Beach Broward Dade Brevard Brevard Brevard Brevard Brevard Brevard Brevard Brevard Brevard Brevard Brevard Duval
.057 4.0 2.0 3.0 3.0 0.25 0.25 0.25
.10 50 200 75, 25 20 500 100 50 50 100 100
'00 30
.028
.114
.043
.014
.Oll
.112
.228
.129
.042
.003
.284
.057
.028
.028
.057
.057
.057
.017
.568
.057
.056
.007
.114
.228
.171
.004
.006 0(.0005) 2F-19 Rev.
36 -'12/20/74
Mind Speed Range (mph)
Chronological Listing 1
50-90 Mfsc.
Trees Douned and Uprooted TABLE VIE STORM DATA DAHACE REPORTS FOR PERIOD OF RECORD:
1950 TO 1972 Dames 4 Hoore Intcnsft Cate orfes 3
100-150 5
150-250 2
SO-I 20 Misc.
4 120-IBO Misc.
Hisc.
Hfsc.
I'artfal Roof Substantial Buildings Dama a~I Sma II Partial Severe
'Weak Buildings Total Home Home Structures Homes
~Dama e
Roof Daces Damn e
Flatten Destro ed 6
225-300 Hisc .
Substantial Bulld Ings It t~d 5
6 I
O y
10 11 12 I
13 na 14 O
'V c
X
~
~
~
~
I I ~
~
~
~
~
~ t I
I II I
I l I I
~
~
I
~
~
TABLE VII (Con't)
Mind Speed Range (mph)
Chronological Listing 1
50-90 Hisc.
Trees Dovned and Uprooted STORH DATA DAHACE REPORTS FOR PERlOD OF RECORD:
1950 TO 1972 D
I Ha~f8 IMc It ~CI rI s 3
100-150 6
225-300 Hisc.
2 80-120 Misc.
4 120-180 5
150-250 Misc.
Misc.
Hisc.
Partial Roof Small Partial Severe Weak Substantial Substantial Buildings Total Ilomc Mome Structures llomes Buildings Buildings Dama e
Roof Dama e
Dama e
Flatten Destro ed Dama ed Destro ed 2o 30 31 32 33 35 36 37 38 39 40 41 42 CD
0
'Mind Speed Range (mph)
Chronological Listing 1
50-90 Misc.
Trees Dovned and Uprooted TABLE VII (Con't)
STORH DATA DAMAGE REPORTS FOR PERIOD OF RECORD:
1950 TO 1972 Uanes 4 Hoore Intensit Cate pries 2
80-120 Hlsc.
3 100-150 Misc.
4 120-180 Misc.
Partial Roof Snail Partial Severe Weak Buildings Total ffone lfone Structures Uones 5
150-250 Hlsc 6
W 225-300 Hisc.
Substant lal Substant lal Buildings Buildings liam 8
~D*t ed X
44 45 47 X
50 51 52 53 54 55 C) 56
TABLE VII (Con't)
STORM DATA DAHACE REPORTS FOR PERIOD OF RECORD:
1950 TO 1972 Dames 6 Hoore Intensit Cate pries lfind Speed Range (mph) 1 50-90 Hisc 2
80-120 Misc 3
100-150 Misc.
4 120-180 Misc 5
150-250 Hisc.
6 225-300~M sc.
Chronological I.isting 57 Trees Dovned and Uprooted Partial Smal I Partial Severe Ucak Substantial Substantial Roof Buildings Total Mome llomc Structures Homes Buildings Buildings Dama e
Roof Dama e
Dama e
Flatten Destro ed Daa~acd Destroyed 58 59 X
X 60 61 62 c
63 X
X 64 66 67 4J 68 I
69 70 C3 c
TABLE VII (Con't)
STORM DATA DAMAGE RFPORTS FOR PERIOD OP RECORD:
1950 TO 1972 Dames 6 Moore lntcnslt Cate pries Mind Speed Range (mph) 1 50-90 Misc.
2 80-120 Misc.
3 4
100-150 Misc.
120-180 Misc.
5 150-250 Misc.
6 225-300 Misc.
Chronological Listing 71 Trees Douned and Uprooted Partial Small Partial Severe
'Weak Substantial Substantial Roof Buildings Total Home llome Structures llomes Buildings Buildings Dana e
Root Dana c
Dam~a.c Flatten Dcstro ed D~ama ed Dcstr~o ed 72 X
X 73 74 75 I
i6
/8 79 80 X
I 1
hJ C)
V X
X X
X
TABLE VII (Con't)
STORM DATA DAMAGE REPORTS FOR PERIOD OF RECORD:
1950 TO 1972 Mind Speed Range (aph)
I 50-90 Misc.
2 80-120 Misc 3
4 100-150 Misc.
120-180 Misc.
5 150-250 Misc 6
225-300 Misc.
Chronologlral I.isting 85 Trees Dovned and Uprooted Part ial Roof SrLil I Par t ia I Severe Wea k Substantial Substant ial Buildings Tota1 Ilone llome Structures Ilosdes Buildings Buildings Daedal Roof Damage Danae Flat ten Destro ed 0~
d 0 "t~d 86 87 X
X 88 89 I
90 91 92.
93 C
94 95 I
96 W
)7
)8 V
c
TABLE VII (CPtf')
STORM DATA DAMAGE RFPORTS FOR PFRIOD OF RFCORD:
1950 TO 1972 Wind Speed Range (mph) 1 50-90 Misc.
2 80-120 Misc 3
100-150 Mfsc 4
120-180 Misc.
5 6
150-250 Misc.
225-300 Misc Chronological Lfstfng 99 Trees DoMned and Uprooted Partial Roof Sma 1 1 Partial Severe Meak Buildings Total liame Mome Structures Momes D
R I
II..
II..D RI II
.~DRIRR ed Subst ant la 1 Substant 1 a 1 Build fngs Bu f ld ings
~D d
Dest~ro ed 100 101 102 103 104 X
X X
X 105 106 107 108 109 C
~
110 ill I'12 113 o
c 115 X
X
~ X X
X 116
TABLE VIII TORNADO INTENSITY CLASSIFICATION Dames b Moore Intensit Class Wind S eed (HPll)
Number of Classified Tornadoes Number After Adju: tu~.nt.
(1)
(2) 50-90 80-120 100-150 120-180 150-225 200-300 34 46 13 0
0 38.7 52.3 14.8
- 10. 2 0
0 (1)
Each tornado is assumed to have the maximum possible wind speed for the Dames and Moore intensity class to which it has been assigned.
(2)
Since fourteen (14) tornadoes were of unknown intensity although reported, the last column reflects those 14 distributed proportionately to those which vere classified by intensity.
I i
II II I
I I
I I
a I I
I I
I I
~
@ g a
II)l I I I l.
I '
400 300 200 100 90 80 70 6$
50
'i
- I
'I
~ '
~ I 40 0.01 0.05 0.1 0.2 0.5 1
10 20 30 50 50 70 9$
Sl 99 95.0 95.9 03.91 FIGURE 2 PERCENT PROBABILITY THAT THE MIND SPEED EXCEEDS h GIVEN VALUE FOR THE EAST COAST OF FLORIDA