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An Examination of Strong Wind Events Over the Last Half-Century at Five National Weather Service Stations near Coastal South Carolina by A. H. Weber, M. J. Parker, and R. L. Buckley Savannah River National Laboratory

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An Examination of Strong Wind Events Over the Last Half-Century at Five National Weather Service Stations near Coastal South Carolina by A. H. Weber, M. J. Parker, and R. L. Buckley Savannah River National Laboratory. Beaufort Wind Scale. Known Events with Significant Effects. - PowerPoint PPT Presentation

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Page 1: Beaufort Wind Scale

An Examination of Strong Wind Events Over the Last Half-Century at Five National Weather Service

Stations near Coastal South Carolina

by

A. H. Weber, M. J. Parker, and R. L. BuckleySavannah River National Laboratory

Page 2: Beaufort Wind Scale

Beaufort Wind ScaleBeaufort Number Description miles/hr. meters/sec. Effect on land Effect at sea

0 Calm < 1 <.45 Still; smoke rises vertically Surface mirror-like 1 Light air 1-3 .45-1.3 Smoke drifts Ripples form

2 Light breeze 4-7 1.8-3.1 Wind felt on face, leaves rustle Small, short wavelets, not breaking

3 Gentle Breeze 8-12 3.6-5.3

Leaves and small twigs move constantly, streamer extended

Large wavelets beginning to break, scattered white horses

4 Moderate Breeze 13-18 5.8-8.0

Raises dust and papers, moves twigs and thin branches

Small but longer waves, fairly frequent white horses

5 Fresh Breeze 19-24 8.5-10.7 Small trees in leaf begin to sway

Moderate waves, distinctly elongated, many white horses, isolated spray

6 Strong Wind 25-31 11.2-13.9 Large branches move, overhead wires whistle, umbrellas hard to control

Large waves begin with extensive white foam crests breaking, spray probable

7 Moderate Gale 32-38 14.3-17.0 Whole trees move, offers

some resistance to walkers Sea heaps up, white foam blown downwind

8 Fresh Gale 39-46 17.4-20.6 Breaks twigs off trees, impedes progress

Moderately high waves, rolling sea, dense streaks of foam, spray

9 Strong Gale 47-54 21.0-24.1 Blows off roof shingles High waves, rolling sea, dense streaks of foam, spray

10 Whole Gale 55-63 24.6-28.1 Trees uprooted, much structural damage

Heavy rolling sea, white with great foam patches, very high waves, much spray reduces visibility

11 Storm 64-72 28.6-32.2 Widespread damage (rare inland)

Extraordinarily high waves, spray impedes visibility

12 Hurricane 73- 32.6- -- Air full of foam and spray, sea entirely white

Page 3: Beaufort Wind Scale

Figure 1: Reconstructed anemometer trace from the Charleston NWS office indicating difference between 1-min averages and relative stability of 10-min average. Speeds are in knots. (Reproduced with permission, Powell et al. (1991)).

Page 4: Beaufort Wind Scale

Known Events with Significant Effects

Name Start Date End Date Smax (mph) Adjusted (mph)

1948 Winter Storm 12 Feb. 1948 17 Feb. 1948 45 NA

Hurricane Gracie 27 Sep. 1959 01 Oct. 1959 46 NA

1965 Winter Storm 23 Feb. 1965 28 Feb. 1965 31 NA

1978 Winter Storm 24 Jan. 1978 29 Jan. 1978 38 NA

Hurricane Hugo 20 Sep. 1989 25 Sep. 1989 52 68

1993 Winter Storm“Storm of the Century”

12 Mar. 1993 17 Mar. 1993 44 NA

Hurricane Floyd 14 Sep. 1999 19 Sep. 1999 47 NA

Hurricane Gaston 27 Aug. 2004 01 Sep. 2004 43 NA

Page 5: Beaufort Wind Scale

Stations Examined for This Study

Station Location Elevation (tower base)

Period of Record

Years of

Record

ASOS Start

Periods of 3-hr

Observation Intervals†

(Latitude, Longitude)

(m Above Sea Level)

(mo/yr) (years) (date) (date)

Charleston, SC

32:54:00 N, 80:02:00 W

12.2 1/45 thru 09/04

59 01 Oct 1995

1965-69* 1975-77*

Wilmington, NC

34:16:00N, 77:54:00W

9.1 1/48 thru 09/04

56 01 Nov 1995

1954-59†† 1965-77*

Augusta, GA

22:22:00N, 81:58:00W

40.2 1/49 thru 09/04

55 01May 1994

1965-73* 1980-81**

Columbia, SC

33:57:00N 81:07:00W

64.9 1/48 thru 09/04

56 01 Dec 1995

1965-72*

Savannah, GA

32:08:00N 81:13:00W

14.0 10/50 thru 09/04

54 01 Apr 1996

1965-77*

†As opposed to the more common 1-hour observation interval. ††Station was down during the nighttime hours including 22:00 -- 05:00 EST from 1954 through approximately 140 days of 1959. *Station reported every three hours beginning 01:00 through 22:00 ** Station reported every three hours beginning 01:00 through 22:00 through half of 1981.

Page 6: Beaufort Wind Scale
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Page 10: Beaufort Wind Scale

Periods Containing High WindsPeriods of Record Containing High Wind Speeds

(S ≥ 25 mph) by Decade for CHS Decade +N5HR +N3HR +N1HR *NRec

1945-1949 11 26 267 43786

1950-1959 40 102 1030 87594

1960-1969 5 23 220 58455

1970-1979 8 20 219 70112

1980-1989 3 15 134 87862

1990-1999 7 19 229 87696

2000-2004 1 4 82 41740

TOTALS 75 209 2181 477245

+NxHR=Number of events of duration “x” hours *NRec=Total number of records for the period

Page 11: Beaufort Wind Scale

Strong Wind Event Types

0

5

10

15

20

25

TropicalStorms

Fronts Front fromDistantLows

DistantLows

Lows

Page 12: Beaufort Wind Scale

Strong Wind Events by Month

0

2

4

6

8

10

12

14

16

18

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Page 13: Beaufort Wind Scale

High Speeds for 1-hr EventsHigh Speeds by Direction Sector for All 1-hr Events

Central Dir (º)

N25 N30 % (>25 mph)

% (>30mph)

0 N 149 47 6.8 8.6

45 NE 47 8 2.2 1.5

90 E 38 11 1.7 2.0

135 SE 51 13 2.3 2.4

180 S 321 84 14.7 15.3

225 SW 451 88 20.7 16.0

270 W 713 180 32.7 32.8

315 NW 411 118 18.8 21.5

(Totals) 2181 549

Page 14: Beaufort Wind Scale

High Speeds for 3-hr StormsHigh Speeds by Direction Sector for 3-hr Storm Events

Central Dir (º)

N25 N30 % (>25 mph)

% (>30mph)

0 N 51 29 5.1 7.4

45 NE 16 5 1.6 1.3

90 E 15 9 1.5 2.3

135 SE 23 10 2.3 2.5

180 S 133 58 13.4 14.7

225 SW 197 58 19.9 14.7

270 W 350 135 35.3 34.3

315 NW 206 90 20.8 22.8

(Totals) 991 394

Page 15: Beaufort Wind Scale

High Speeds for 5-hr StormsHigh Speeds by Direction Sector for 5-hr Storm Events

Central Dir (º)

N25 N30 % (>25 mph)

% (>30mph)

0 N 31 19 5.5 6.8

45 NE 6 2 1.1 0.7

90 E 8 5 1.4 1.8

135 SE 12 7 2.1 2.5

180 S 75 42 13.4 15.1

225 SW 92 36 16.5 12.9

270 W 194 92 34.7 33.1

315 NW 141 75 25.2 27.0

(Totals) 559 278

Page 16: Beaufort Wind Scale

Hourly Wind Speeds for Return Periods

. Maximum Probable Wind Speed (mph) by Wind Direction

Return Period (Years)

ALL Directions (mph)

S through NW Sector (mph)

NE through S Sector (mph)

5 44 41 38

10 50 47 45

25 60 56 54

50 68 64 62

100 78 73 71

150 84 79 76

200 89 84 81

500 105 100 96

1,000 120 115 110

2,000 136 132 125

5,000 161 158 149

10,000 183 182 170

Page 17: Beaufort Wind Scale
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Spect r al Dens i t y of MEAN_ EXC_ SPD

0. 050. 060. 070. 080. 090. 100. 110. 120. 130. 140. 150. 160. 170. 180. 190. 200. 210. 220. 230. 240. 250. 260. 270. 280. 290. 300. 310. 320. 330. 340. 350. 360. 370. 380. 390. 40

YEARS

0 10 20 30

Spect r al Dens i t y of MEAN_ EXC_ SPD

0. 050. 060. 070. 080. 090. 100. 110. 120. 130. 140. 150. 160. 170. 180. 190. 200. 210. 220. 230. 240. 250. 260. 270. 280. 290. 300. 310. 320. 330. 340. 350. 360. 370. 380. 390. 40

Page 19: Beaufort Wind Scale

Conclusions

• Meteorological data obtained from CHS, ILM, AGS, CAE, and SAV.

• Periods of > five hours with speeds > 25 mph were studied: February and March are worst, also August and September.

• Worst case: Category IV-V hurricane to strike just to the south of a target at a high forward speed.