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Shelf Width, Shoreline Curvature, and Hurricanes: Continued Development of a New Hurricane Impact Scale David M. Bush 1, Robert S. Young 2 , and Chester W. Jackson 1 1 State University of West Georgia 2 Western Carolina University

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Presentation Transcript
slide1

Shelf Width, Shoreline Curvature, and Hurricanes: Continued Development of a New Hurricane Impact Scale

David M. Bush1, Robert S. Young2, and Chester W. Jackson1

1State University of West Georgia

2Western Carolina University

recent nc hurricanes source noaa tropical prediction center reports
Recent NC HurricanesSource: NOAA Tropical Prediction Center Reports

Several similarly sized hurricanes have hit the North Carolina coast in recent years with very different impacts.

slide3

Some of the difference is due to the shoreline setting. Here is the retreating shoreline and overwash apron of Oak Island.

the saffir simpson scale
The Saffir-Simpson Scale

The classical way to rank hurricanes is the Saffir-Simpson Scale, fine for hurricanes over open water but

not so good with predicting erosion and overwash impacts at landfall.

hurricane impact scale
Hurricane Impact Scale

The Hurricane Impact Scale would consider storm surge height and storm surge spread (length of shoreline

affected), as well as the Saffir-Simpson Scale, to rank hurricanes.

slide7

The important controls on storm surge at landfall are: (1) storm physical characteristics, (2) movement of

the storm, and (3) shape of the shoreline relative to storm track.

slide8

Shelf width and shoreline shape are two

important controls on storm surge:

Wide shelf = higher storm surge

Narrow shelf = lower storm surge

Concave shoreline = higher storm surge

Straight or convex shoreline = lower

storm surge

slide9

miles along coast

Hurricane Opal hit a curved stretch of the Florida panhandle in 1995 and clearly shows a classic storm surge

profile on a shoreline with a curvature at a scale matching the size of the hurricane.

his applied

Factors

Andrew

Hugo

Frederic

Opal

SSS (wind)

4

4

3

3

Surge Height

(above SHT/rank)

13.6/4

10.4/3

15.4/4

18.4/5

Surge Spread

1

5

3

4

HIS Rating

9

12

10

12

Normalized HIS

3.0

4.0

3.3

4.0

HIS Applied

Applying the HIS for recent major storms shows that the impacts of the storms at landfall were at scales

somewhat different than their Saffir-Simpson Scale category rankings.

fran vs floyd

Factors

Fran

Floyd

SSS (wind)

3

2

Surge Height (ft above SHT/rank)

6.5/2

5.8/2

Surge Spread

1

1

HIS Rating

6

5

Normalized HIS

2.0

1.7

Fran vs. Floyd

The same is true for Hurricanes Fran and Floyd. Most of Floyd’s damage was from rainfall which is not

considered by the Hurricane Impact Scale.

shoreline curvature index
Shoreline Curvature Index

C

Land

Sea

P

Curvature = C/P

Future work calls for applying a shoreline curvature parameter. Shoreline curvature may be quantified by dividing the chord length (C) by the perpendicular length (P) for various coastal segments.

slide13

The ratio of shelf width (light blue line) to shoreline curvature (C/P) yields a width/curvature index (white numbers). This index has yet to be incorporated into the HIS.

his modes
Predictive (pre-storm)

Shelf width

Shoreline curvature (at several scales)

Predicted storm track

Predicted storm strength

Predicted storm forward speed

Historical storms

Range of HIS scales

Comparative (post-storm)

Field measurements

Surge height

Surge spread

Wind speeds NHC/NWS

Single HIS rank assigned

HIS Modes
slide15

With shoreline settings quantified, local coastal managers will be able to predict the range of possible landfall impacts of a hurricane for their particular stretch of shoreline, given the National Hurricane Center’s predicted strength of the hurricane.

in terms of earthquakes
In Terms of Earthquakes
  • Saffir-Simpson Scale = Richter Scale
    • Measure of energy released
    • Absolute scale
  • Hurricane Impact Scale = Mercalli Scale
    • Measure of impacts
    • How the storm was actually felt
  • Both EQ scales are post-event measurements
  • SSS and HIS both predictive and comparative
  • HIS attempting to refine predictive capability
another way to look at it
Another Way to Look at it:
  • Every hurricane is different, has its own personality
  • SSS doesn’t take that into account, too rigid
  • SLOSH maps good for their application (evacuation and sheltering) but too inclusive
  • HIS will consider and predict “hurricanes as individuals” impacts
conclusions i
Conclusions I
  • SSS good for indicating hurricane strength
  • Storm surge height and extent is a good indicator of energy flux
  • Many controls on storm surge not handled by SSS
  • New scale needed to work in conjunction with SSS
conclusions ii
Conclusions II
  • Same storm in different setting means different impacts
  • Hurricane Impact Scale will allow better communication of potential storm impacts as storm approaches
  • Pre-storm, a range of HIS values given
  • Post-storm, one final HIS rank determined
acknowledgements
Acknowledgements
  • Federal Emergency Management Agency
  • Public Entity Risk Institute
  • Natural Hazards Center
  • Orrin Pilkey, Duke University
  • Wil Shaffer, NOAA
  • Steve Lyles, NOAA/NOS