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Long Term Trends in National Hurricane Center Watches and Warnings Mark DeMaria, NOAA/NESDIS/StAR, Fort Collins, CO and James L. Franklin, NOAA/NCEP/TPC, Miami, FL Presented at the Interdepartmental Hurricane Conference March 8, 2007 Outline Introduction Data and Verification Methods

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Long Term Trends in National Hurricane Center Watches and Warnings

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Long Term Trends in National Hurricane Center

Watches and Warnings

Mark DeMaria, NOAA/NESDIS/StAR, Fort Collins, CO

and

James L. Franklin, NOAA/NCEP/TPC, Miami, FL

Presented at the

Interdepartmental Hurricane Conference

March 8, 2007


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Outline

  • Introduction

  • Data and Verification Methods

    • 1963-2006 sample

  • Verification and Long Term Trends

  • Conclusions


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Hurricane Watches and Warnings

  • Watch – hurricane conditions are possible within 36 hours

  • Warning – hurricane conditions are expected within 24 hours

  • Watches and Warnings (WWs) re-evaluated every 6 hours

    • Can be updated at any time in special advisories

  • End points of WWs selected from coastal “breakpoints”


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Input to Watches and Warnings

  • Major considerations

    • Forecast track, intensity, wind structure

    • Forecast uncertainty

      • Larger area included than receives hurricane winds

  • Other factors

    • Time of day

      • 5 PM warnings preferred over 11 PM

    • Storm surge and evacuation lead times

    • Input from coordination call


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Data and VerificationMethods

  • All WW breakpoints for contiguous U.S. digitized for 1965-2006

    • Cindy 1963 and Cleo 1964 also included

  • 183 coastal breakpoints used to define coastline

    • Supplemented with 157 intermediate points

      • Brownsville, Texas to Eastport, Maine = 3600 nmi

  • “Observed” hurricane winds from NHC data

    • NHC best track position, intensity

    • Operational 64 kt wind radii

      • Best track radii since 2004


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Breakpoint 2

Breakpoint 1

“Observed” Hurricane

Wind Region


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WW Length and Lead Time

  • WW Length

    • Size of WW for an individual advisory

    • Total length with WW at any time in storm lifetime

  • WW Lead Time

    • Time between first issuance of WW and arrival of hurricane winds

      • Valid only for points that received hurricane winds


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Lengths of Hurricane Warnings from Individual Advisories1963-2006

N=890


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Top Five Warning Lengths

  • Gloria 1985 Sep 27 1053 nmi

  • Floyd 1999 Sep 16 1045 nmi

  • Bob 1991 Aug 18 984 nmi

  • Charley 2004 Aug 13 906 nmi

  • Belle 1976 Aug 10 838 nmi


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Hurricane Warning Length Decadal Averages


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Storm-Average Warning Lead Time(time from when warning was first issued at a location to arrival of hurricane winds)


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Hurricane Warning Lead Time Decadal Averages


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Hurricane Watch Length and Lead TimeDecadal Averages

Length Lead Time


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Warning and Watch Statistics(2000-2006)

  • Average individual warning length 290 nmi

  • Average storm-total warning length 362 nmi

  • Average storm-total length w\ hurricane winds 89 nmi

  • Prob. of warned point receiving hurricane winds 25%

  • Lead time of hurricane warning 34 hr

  • Average individual watch length 210 nmi

  • Average storm-total watch length 425 nmi

  • Average storm-total length w\ hurricane winds 85 nmi

  • Prob. of watch point receiving hurricane winds 20%

  • Lead time of hurricane watch 50 hr


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Conclusions

  • The average length of NHC hurricane warnings has decreased in the 2000’s reversing a 35 year trend of increases

    • Average warning length is 290 nmi

  • The average lead times of warnings and watches are now 34 hr and 50 hr

    • Long-term averages are 27 hr and 40 hr

  • Warned location has 1 in 4 chance of hurricane winds

  • Watch location has 1 in 5 chance of hurricane winds


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