# Presentation: 273325

## 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
- 1963-2006 sample
- Verification and Long Term Trends
- Conclusions

## 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”

## Slide 4

## Slide 5

## 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

- 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

## Breakpoint 1

**Breakpoint 1**

**Breakpoint 2**

**“****Observed” Hurricane **
**Wind Region**

## 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

## Lengths of Hurricane Warnings from Individual Advisories1963-2006

**N=890**

## 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

## Hurricane Warning Length Decadal Averages

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

## Hurricane Warning Lead Time Decadal Averages

## Hurricane Watch Length and Lead TimeDecadal Averages

**           ****Length                                                    Lead Time**

## 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

- 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