a wind gust factor database and the development of associated gfe tools jonathan blaes 16 november...
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A Wind Gust Factor Database and the Development of Associated GFE Tools
Jonathan Blaes16 November 2012
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The Problem with Forecasting TC Wind Gusts
• Lack of science• Varying forecast strategies and
tools• Limited external consistency• Limited collaboration• Limited shift to shift forecast
consistency• Time/efficiency constraints• TC Wind forecasts are a mess
too!
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Examining Gust Factors
We examined the sustained winds, wind gusts, peak winds, and gust factors for ten tropical cyclones.
A table of the tropical cyclones examined along with a map of their tracks is shown.
Storm Name Date Landfall Winds at Landfall GF Obs
Irene 27-Aug-11 NC 85 MPH 1055
Hanna 6-Sep-08 NC/SC 70 MPH 917
Ernesto 30-Aug-06 South FL 70 MPH 1107
Gaston 29-Aug-04 SC 75 MPH 1164
Charley 13-Aug-04 FL 75 MPH 290
Isabel 18-Sep-03 NC 105 MPH 3095
Floyd 16-Sep-99 NC 105 MPH 1283
Dennis 4-Sep-99 NC 105 MPH 5045
Fran 5-Sep-96 NC 115 MPH 551
Bertha 12-Jul-96 NC 105 MPH 431
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Methods
• Observations of winds and wind gusts from between 21 and 45 ASOS or AWOS METARs were collected for each storm
• Locations varied for each storm, tried to capture the variations in the wind field.
• Only used hourly METARs, no special observations
• The hourly wind gust factor (GF) was computed as the ratio of the wind gust to the sustained wind speed.
• Total of 14,938 gust factors were computed
• The various station locations and TCs result in a data set that contains varied sensor types, roughness length, exposure, stability, wind trajectory, etc.
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Sustained Wind vs. Gust Factors
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Gust Factor Frequency
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Wind Speed vs. Gust Factor Occurrences
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Mean Gust Factor
The mean gust factor value of the 10 storms examined was 1.47 which compares closely to several previous studies.
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Gust Factor Regression Equations
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Notes from the Gust Factor Database
• Minimum GF observed was ~ 1.1 with only 17.9% or 2,678/14,938 observations with a gust factor of less than 1.2.
• The GF is varied at low sustained wind speeds but generally converges and decreases with increasing sustained wind speed.
• A one size fits all gust factor does not apply• Large variation in GF with changes in sustained winds.Sustained winds 10-20 MPH – GF typically range from 1.2 to 1.6Sustained winds 20-30 MPH – GF typically range from 1.1 to 1.4Sustained winds 30-40 MPH – GF typically range from 1.1 to 1.3• Large fraction (41.5%) of GF occur in the 1.2 to 1.6 range • The average GF among the 14,938 observations was 1.47.• A regression curve was developed: y = -0.173ln(x) + 1.9506
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TCWindGust and WindGust_from_WindGustFactor tools
• This dataset has spawned the development of several GFE tools• Two pathways
1) directly create the WindGust grid based on GF x Wind2) create semi persistent WindGustFactor grids are used to
create the WindGust grid based on GF x Wind (next talk)
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TCWindGust and WindGust_from_WindGustFactor tools
• Both methods provide the user with multiple GF options. 1) “CSTAR Regression" is based on a regression equation developed at RAH from 14,938 gust factors • 2) "CSTAR Mean of 1.47" based on the same RAH data set but
uses a simple average of all GFs.• 3) The remaining options are based on research by Harper et al. (2008) which provided examined the peak gust for various exposures.
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Hurricane Sandy
Examined 12 ASOS/AWOS in NC/SCTotal of 1,369 gust factorsSustained winds rather weakMean GF of 1.58y = -0.307ln(x) + 2.4539
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Hurricane Sandy
Sandy shown in bold red
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Next Steps
• Continue refinements to the tools• How to handle winds less than 10 MPH? GF of 1.55• How to handle higher end winds >70 MPH as GF asymptotes out
toward 1.0. GF of 1.2 is reached at 76.6 MPH while a GF of 1.15 is reached at 102.3 MPH
• Examine over water GF and incorporate into tools• Need to add quantitative data for over water environments. AKQ has a
dataset or we can build upon prior research which suggest over water GF ranges from 1.1 to 1.2
• Examine GF associated with Sandy in NJ/NY• Develop training materials• Explore some sort of verification • Test the methodology at WFOs ILM, RAH, MHX, and MFL during
the 2013 TC season
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Acknowledgements
• Thanks to student volunteer Dan Brown for examining nearly all of the ~15K gust factors and generating most of the charts as well.
• NC State student volunteers Rebecca Duell and Lindsey Anderson helped develop the overall methodology and completed the analysis of Hurricane Irene.
• Bryce Tyner and Dr Aiyyer• Collaborative Investigator Reid Hawkins• Rest of the CSTAR TC Winds team
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ReferencesDurst, C. S., 1960: Wind speeds over short periods of time. Meteor. Mag., 89, 181–186.Conder, M. R., and R. E. Peterson, 2000: Comparison of Gust Factor Data from Hurricanes. Preprints, 24th AMS Conf. on Hurricanes and Tropical Meteor. Fort Lauderdale, FL. J53-J54. [Available online at http://www.atmo.ttu.edu/conder/documents/Hurr-J7.5.PDF] Krayer, William R., Richard D. Marshall, 1992: Gust factors applied to hurricane winds. Bull. Amer. Meteor. Soc., 73, 613–618. [Available online at http://dx.doi.org/10.1175/1520-0477(1992)073<0613:GFATHW>2.0.CO;2] Paulsen, B. M., J. L. Schroeder, 2005: An Examination of Tropical and Extratropical Gust Factors and the Associated Wind Speed Histograms. J. Appl. Meteor., 44, 270–280.[Available online at http://journals.ametsoc.org/doi/pdf/10.1175/JAM2199.1] Powell, Mark D., Samuel H. Houston, Timothy A. Reinhold, 1996: Hurricane Andrew's Landfall in South Florida. Part I: Standardizing Measurements for Documentation of Surface Wind Fields. Wea. Forecasting, 11, 304–328. [Available online athttp://dx.doi.org/10.1175/1520-0434(1996)011<0304:HALISF>2.0.CO;2] Schroeder, J. L., M. R. Conder, and J. R. Howard, 2002: "Additional Insights into Hurricane Gust Factors,” Preprints, Twenty-Fifth Conference on Hurricanes and Tropical Meteorology, San Diego, California, 39-40. Vickery, P.J., and P.F. Skerlj, 2005,: Hurricane gust factors revisited, J. Struct. Eng., 131, 825-832.[Available online at http://www.asce.org/uploadedFiles/Communications-NEW/Hurricane/Hurricane_Gust_Factors_Revisited.pdf] Yu, Bo, Arindam Gan Chowdhury, 2009: Gust Factors and Turbulence Intensities for the Tropical Cyclone Environment. J. Appl. Meteor. Climatol., 48, 534–552. [Available online at http://dx.doi.org/10.1175/2008JAMC1906.1]
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Questions ?
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Extra Slides
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