The Re-analysis The Re-analysis of Hurricane Andrew (1992)of Hurricane Andrew (1992)

Chris Landsea

NOAA/Hurricane Research Division

Miami, Florida, USA

NHC Best Track Change Committee

1 August 2002

Contributors: Pete Black, Peter Dodge, Jason Dunion, James Franklin, Brian Jarvinen, Tim Olander, Mark Powell, Chris Velden

Comments: William Bredemeyer, Steve Feuer, Paul Hebert, Sam Houston, Charlie Neumann, Hugh Willoughby

Why re-analyze the Atlantic hurricanes and Andrew? Summary of changes suggested Flight-level wind to surface extrapolation Feature tracking from the Miami radar Pressure-wind relationships Satellite intensity estimates Storm surge and SLOSH implications Estimates of intensity from damage surveys Discussion of uncertainties

The Re-analysis The Re-analysis of Hurricane Andrew (1992)of Hurricane Andrew (1992)

Work of Jose Partagas: Historical Reconstruction from 1851-1910

WHAT IS THE INTENSITY OF A WHAT IS THE INTENSITY OF A TROPICAL CYCLONE?TROPICAL CYCLONE?

Maximum sustained surface wind: Maximum wind, averaged over 1 minute interval at an altitude of 33 ft (10 m), associated with the circulation of the tropical cyclone at a given point in time.

With very, very few exceptions, direct observations of the maximum sustained surface wind in a tropical cyclone are not available.

HOW DO WE ESTIMATE INTENSITY?HOW DO WE ESTIMATE INTENSITY?HOW DO WE ESTIMATE INTENSITY?HOW DO WE ESTIMATE INTENSITY?

Satellite imagery using the Dvorak technique.

Aircraft reconnaissance flight-level winds

GPS dropwindsondes

Revised Best Track

Best Track Winds

Best Track Pressures

Table 1: Revisions in HURDAT and at landfall in the Bahamas and the United States forHurricane Andrew, August 16-28, 1992. The format is that the entire storm is presented. Unaltered values in best track do not have a repeated line. For values that are changed, theoriginal line of data is first presented and the revised line of data is shown next along with "**"that indicate which data are altered.

HURDAT Data

54545 08/16/1992 M=13 2 SNBR=1158 ANDREW XING=1 SSS=454545 08/16/1992 M=13 2 SNBR=1158 ANDREW XING=1 SSS=5 *

54550 08/16* 0 0 0 0* 0 0 0 0* 0 0 0 0*108 355 25 101054555 08/17*112 374 30 1009*117 396 30 1008*123 420 35 1006*131 442 35 100354560 08/18*136 462 40 1002*141 480 45 1001*146 499 45 1000*154 518 45 100054565 08/19*163 535 45 1001*172 553 45 1002*180 569 45 1005*188 583 45 100754570 08/20*198 593 40 1011*207 600 40 1013*217 607 40 1015*225 615 40 101454575 08/21*232 624 45 1014*239 633 45 1010*244 642 50 1007*248 649 50 1004

54580 08/22*253 659 55 1000*256 670 60 994*258 683 70 981*257 697 80 96954580 08/22*253 659 55 1000*256 670 65 994*258 683 80 981*257 697 95 969 ** ** **

54585 08/23*256 711 90 961*255 725 105 947*254 742 120 933*254 758 135 92254585 08/23*256 711 110 961*255 725 125 947*254 742 140 933*254 758 150 922 *** *** *** ***

54590 08/24*254 775 125 930*254 793 120 937*256 812 110 951*258 831 115 94754590 08/24*254 775 130 930*254 793 130 937*256 812 115 951*258 831 115 947 *** *** ***

54595 08/25*262 850 115 943*266 867 115 948*272 882 115 946*278 896 120 94154595 08/25*262 850 115 943*266 867 115 948*272 882 120 946*278 896 125 941 *** ***

54600 08/26*285 905 120 937*292 913 115 955*301 917 80 973*309 916 50 99154600 08/26*285 905 125 937*292 913 120 955*301 917 80 973*309 916 50 991 *** ***

54605 08/27*315 911 35 995*321 905 30 997*328 896 30 998*336 884 25 99954610 08/28*344 867 20 1000*354 840 20 1000* 0 0 0 0* 0 0 0 0

54615 HRCFL4BFL3 LA354615 HRCFL5BFL4 LA3 ********

54545 08/16/1992 M=13 2 SNBR=1158 ANDREW XING=1 SSS=454545 08/16/1992 M=13 2 SNBR=1158 ANDREW XING=1 SSS=5 *

54550 08/16* 0 0 0 0* 0 0 0 0* 0 0 0 0*108 355 25 101054555 08/17*112 374 30 1009*117 396 30 1008*123 420 35 1006*131 442 35 100354560 08/18*136 462 40 1002*141 480 45 1001*146 499 45 1000*154 518 45 100054565 08/19*163 535 45 1001*172 553 45 1002*180 569 45 1005*188 583 45 100754570 08/20*198 593 40 1011*207 600 40 1013*217 607 40 1015*225 615 40 101454575 08/21*232 624 45 1014*239 633 45 1010*244 642 50 1007*248 649 50 1004

54580 08/22*253 659 55 1000*256 670 60 994*258 683 70 981*257 697 80 96954580 08/22*253 659 55 1000*256 670 65 994*258 683 80 981*257 697 95 969 ** ** **

54585 08/23*256 711 90 961*255 725 105 947*254 742 120 933*254 758 135 92254585 08/23*256 711 110 961*255 725 125 947*254 742 140 933*254 758 150 922 *** *** *** ***

54590 08/24*254 775 125 930*254 793 120 937*256 812 110 951*258 831 115 94754590 08/24*254 775 130 930*254 793 130 937*256 812 115 951*258 831 115 947 *** *** ***

54595 08/25*262 850 115 943*266 867 115 948*272 882 115 946*278 896 120 94154595 08/25*262 850 115 943*266 867 115 948*272 882 120 946*278 896 125 941 *** ***

54600 08/26*285 905 120 937*292 913 115 955*301 917 80 973*309 916 50 99154600 08/26*285 905 125 937*292 913 120 955*301 917 80 973*309 916 50 991 *** ***

54605 08/27*315 911 35 995*321 905 30 997*328 896 30 998*336 884 25 99954610 08/28*344 867 20 1000*354 840 20 1000* 0 0 0 0* 0 0 0 0

54615 HRCFL4BFL3 LA354615 HRCFL5BFL4 LA3 ********

Revised HURDAT

File

Landfall Data

Date/Time Lat Lon Max Saffir- Central Landfall States Winds Simpson Pressure Location Affected8/23/2100Z 25.4N 76.6W 130kt 4 923mb Eleuthera, Ba ---8/23/2100Z 25.4N 76.6W 140kt 5 923mb Eleuthera, Ba --- *** *

8/24/0100Z 25.4N 77.8W 125kt 4 931mb Barry Is., Ba ---8/24/0100Z 25.4N 77.8W 130kt 4 931mb Barry Is., Ba —-- ***

8/24/0905Z 25.5N 80.3W 125kt 4 922mb Homestead CFL4, BFL38/24/0905Z 25.5N 80.3W 145kt 5 922mb Homestead CFL5, BFL4 *** * **** ****

8/26/0830Z 29.6N 91.5W 105kt 3 956mb Pt. Chevreuil LA38/26/0830Z 29.6N 91.5W 110kt 3 956mb Pt. Chevreuil LA3 ***

Landfall Data

Date/Time Lat Lon Max Saffir- Central Landfall States Winds Simpson Pressure Location Affected8/23/2100Z 25.4N 76.6W 130kt 4 923mb Eleuthera, Ba ---8/23/2100Z 25.4N 76.6W 140kt 5 923mb Eleuthera, Ba --- *** *

8/24/0100Z 25.4N 77.8W 125kt 4 931mb Barry Is., Ba ---8/24/0100Z 25.4N 77.8W 130kt 4 931mb Barry Is., Ba —-- ***

8/24/0905Z 25.5N 80.3W 125kt 4 922mb Homestead CFL4, BFL38/24/0905Z 25.5N 80.3W 145kt 5 922mb Homestead CFL5, BFL4 *** * **** ****

8/26/0830Z 29.6N 91.5W 105kt 3 956mb Pt. Chevreuil LA38/26/0830Z 29.6N 91.5W 110kt 3 956mb Pt. Chevreuil LA3 ***

Revised Landfall Data

In the early 1990’s, reduction factors used by NHC ranged from 75%-90% of the flight-level wind.

Powell and Black (1990) concluded 63-73% for 700mb to surface reduction factor, but had few eyewall high-wind cases.

EYEWALL SCHEMATICEYEWALL SCHEMATIC

AIRCRAFT TRACK

DROPSONDE TRAJECTORY

100 90 80 70 10000 ft

~1-2 miles

AVERAGE OF 357 GPS DROPSONDE PROFILES IN THE HURRICANE EYEWALL.

ON AVERAGE, THE SURFACE WIND IS 90% OF THE WIND AT 700 MB AIRCRAFT RECONNAISSANCE LEVELS (75-80% AT LOWER ALTITUDES).

Franklin et al. (2002)

EYEWALL STRUCTURE CAN VARY SIGNIFICANTLY FROM STORM TO STORM, OR EVEN DURING DIFFERENT STAGES OF THE LIFE CYCLE OF A SINGLE STORM.

Franklin et al. (2002)

Implications for AndrewImplications for Andrew

Franklin et al. (2001)

IMPLICATIONS FOR ANDREW

Aircraft measured wind of 162 kt at 10,000 ft at 4:10 am, ~1 hr prior to landfall.

If Andrew were occurring today, NHC would estimate a surface sustained wind of ~145 kt (~165 mph), based on taking 90% of the recon wind speed.

Franklin, Pers. Comm.

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Bin Ave (R/Rmax: 0.1 bins)

Data

Inside Flight-Level RMW

Apply x1.3 boost if R/Rmax <0.25 and R/Rmax>=0

Apply polynomial if R/Rmax <=2.0 and

Outside Flight Level

UMBL = U700 [2.31x10 -1(R/RMW) 3 - 6.82x10 -1(R/RMW)2 + 3.04x10-1(R/RMW) + 1.26]

Distance as a Function of RMW

MBLto

700mbRatio

Step 1: Flight Level to a Mean Boundary Layer (0 to 500m)

Dunion, Landsea, Houston (2002); Dunion and Powell (2002)

USFC = UMBL[-2.84x10 -7 (UMBL)3 + 1.58x10 -4 (UMBL)2 - 1.25x10 -2 (UMBL) + 1.08]

0.50

0.60

0.70

0.80

0.90

1.00

1.10

0 10 20 30 40 50 60 70 80

Data

Bin Ave (w/ 5 min gust)

HRD PBL Model

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Use 0.9(W MBL) if

WMBL >72 ms-1

Apply polynomial

if WMBL >=55 ms-1

and <=72 ms-1

Use PBL model if

WMBL <55 ms-1

MBL Wind Speed (ms-1)

MBL Wind Speed (mph)

Surf

ace

Win

d Sp

eed

/ MB

L W

ind

Spee

d

Step 2: Mean Boundary Layer (0 to 500m) to the Surface

Dunion, Landsea, Houston (2002); Dunion and Powell (2002)

New H*WIND Analysis For Hurricane Andrew

150 kt – 93% of flight level

Some New Hurricane Andrew Data:Radar Feature Tracking

Comparison of Flight Level Data (in Red)

To Radar Feature Data (in Green)

Pressure-Wind

Relationships:

Where Does Andrew Fall?

Brown and Franklin (2002)

Large versus Small Hurricanes:Implication for Pressure-Wind Relationship

Hurricane Andrew -Satellite Dvorak Estimates

127 kt/935 mb

Date/Time Raw T number Dvorak Winds Scene Type

23 / 1201 6.5 127 kt Clear eye

23 / 1331 6.2 120 Clear eye

23 / 1431 6.2 120 Clear eye

23 / 1531 6.1 117 Clear eye

23 / 1631 6.1 117 Clear eye

23 / 1701 6.1 117 Clear eye

23 / 1801 6.1 117 Clear eye

23 / 1901 6.1 117 Clear eye

23 / 2001 6.2 120 Clear eye

23 / 2101 6.2 120 Clear eye

23 / 2201 5.7 107 Ragged eye

23 / 2301 5.2 95 Ragged eye

24 / 0001 5.1 92 Obscured eye

24 / 0131 4.8 84 Obscured eye

24 / 0201 4.8 84 CDO

24 / 0301 4.8 84 CDO

24 / 0401 4.8 84 CDO

24 / 0501 4.8 84 CDO

24 / 0601 5.0 90 Obscured eye

24 / 0701 5.1 92 Obscured eye

24 / 0801 5.4 99 Obscured eye

24 / 0901 6.7 132 Clear eye

24 / 1001 5.7 107 Ragged eye

24 / 1101 5.5 107 Ragged eye

24 / 1201 4.8 84 Obscured eye

ObjectiveDvorak

Technique

Hurricane Andrew’sStorm Surge

And SLOSH Runs

Structural DamageSurveys of Hurricane Andrew

Two Main Structural Damage

Swaths:Naranja Lakes and

Cutler Ridge/Tamiami

Fujita (1992); Wakimoto and Black (1994)

Two Main Structural Damage

Swaths:Naranja Lakes and

Cutler Ridge/Tamiami

Fujita (1992); Wakimoto and Black (1994)

Flight-level wind to surface extrapolation 145 kt (+10)

Feature tracking from the Miami radar145 kt (+15) Pressure-wind relationships 145 kt (+20)

Satellite intensity estimates 145 kt (+20) Storm surge and SLOSH implications 145 kt (+25)

Structural damage survey estimates 135 kt (+30)

The Re-analysis The Re-analysis of Hurricane Andrew (1992)of Hurricane Andrew (1992)

CONCLUSIONS

* Andrew’s intensity at landfall (and elsewhere) will never be known with certainty.

*Andrew’s intensity at landfall is VERY LIKELY to be in therange of 136 to 155 kt (Category 5) for the maximum sustainedsurface winds in South Florida.

*The single best estimate of intensity at landfall is 145 kt.

* It is quite UNLIKELY that Andrew was a 125 kt (Category 4)as originally thought.

        Atlantic Hurricane Re-Analysis Project              

1.Documentation 2.Data By Year and Storm 3.Reference

Picture from: "Florida's Hurricane History", by Jay Barnes

http://www.aoml.noaa.gov/hrd/hurdat/index.html

GPS DROPWINDSONDEGPS DROPWINDSONDE Developed in conjunction with the

NOAA Gulfstream-IV jet aircraft. First systematic use for intensity was in 1998’s Hurricane Bonnie.

GPS dropsondes provide, for the first time, direct measurements of the winds at low levels in the hurricane eyewall.

Dropsonde data reveal that the structure of the eyewall is very complex, and can vary tremendously from storm to storm.

Neumann et al. (1999)

Observational Platforms for Atlantic Hurricanes

Incorrect IntensityAnd Location

At Landfall

Too Rapid DuringLast 6 Hours

Pressure-Wind Relationship

Atlantic Major Hurricanes

Landsea (1993)

Bias-removed

HOW CAN WE USE THE DROPSONDE DATA TO IMPROVE OUR OPERATIONAL INTENSITY ESTIMATES?

INTERPRETATION OF FLIGHT-LEVEL WINDS

DIRECT MEASURMENTS OF SURFACE WINDS

RECON FLIGHT-LEVEL WINDS

HURRICANE GEORGES 9/20/98 20-23Z

105 kt

90 kt

90 kt95 kt

But nobody lives at 10,000 ft.

How can we use flight-level data to estimate surface winds?

ATLANTIC WIND/PRESSURE RELATIONSHIPS

Winds (knots) computed from regional P/W relationships

P(MB) GLFMEX <25N 25-35N 35-45N KRAFT P(MB) P(IN)

960 100 100 94 90 102 960 28.35

1)For GLFMEX: Wind(knots)=10.627*(1013-p)**0.5640 Sample size =664; r=0.991

2)For <25N Wind(knots)=12.016*(1013-p)**0.5337 Sample size =1033; r=0.994

3)For 25-35N Wind(knots)=14.172*(1013-p)**0.4778 Sample size =922; r=0.996

4)For 35-45N Wind(knots)=16.086*(1013-p)**0.4333 Sample size =492; r=0.974

5)For Kraft Wind(knots)=14.000*(1013-p)**0.5000 Sample size =13; r= ??

DROPSONDES WILL FUNCTION EVEN IN THE TURBULENT CONDITIONS OF THE HURRICANE EYEWALL.

211 MPH: STRONGEST WIND EVER OBSERVED BY A DROPSONDE IN A HURRICANE.

Dvorak TechniqueDvorak Technique

Tropical cyclones have characteristic cloud patterns that correspond to stages of development

and certain intensities.