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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 Outline Introduction Data and Verification Methods

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Presentation Transcript
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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
Outline
  • Introduction
  • Data and Verification Methods
    • 1963-2006 sample
  • Verification and Long Term Trends
  • Conclusions
hurricane watches and warnings
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”
input to watches and warnings
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
data and verification methods
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

ww length and lead time
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
top five warning lengths
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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Storm-Average Warning Lead Time(time from when warning was first issued at a location to arrival of hurricane winds)
warning and watch statistics 2000 2006
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
conclusions
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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