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

Work of Jose Partagas: Historical Reconstruction from

WHAT IS THE INTENSITY OF A 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? Satellite imagery using the Dvorak technique. Aircraft reconnaissance flight-level winds GPS dropwindsondes

Revised Best Track

Best Track Winds Best Track Pressures

Revised HURDAT File

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 SCHEMATIC AIRCRAFT TRACK DROPSONDE TRAJECTORY 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 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.

Distance as a Function of RMW MBL to 700mb Ratio Step 1: Flight Level to a Mean Boundary Layer (0 to 500m) Dunion, Landsea, Houston (2002); Dunion and Powell (2002)

MBL Wind Speed (ms -1 ) MBL Wind Speed (mph) Surface Wind Speed / MBL Wind Speed 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

Objective Dvorak Technique

Hurricane Andrew’s Storm Surge And SLOSH Runs

Structural Damage Surveys 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 radar 145 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)

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 the range of 136 to 155 kt (Category 5) for the maximum sustained surface 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.DocumentationDocumentation 2.Data By Year and StormData By Year and Storm 3.ReferenceReference Picture from: "Florida's Hurricane History", by Jay Barnes

GPS 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 Intensity And Location At Landfall

Too Rapid During Last 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/ Z 105 kt 90 kt 95 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) )For GLFMEX: Wind(knots)=10.627*(1013-p)** Sample size =664; r= )For <25N Wind(knots)=12.016*(1013-p)** Sample size =1033; r= )For 25-35N Wind(knots)=14.172*(1013-p)** Sample size =922; r= )For 35-45N Wind(knots)=16.086*(1013-p)** Sample size =492; r= )For Kraft Wind(knots)=14.000*(1013-p)** 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 Technique Tropical cyclones have characteristic cloud patterns that correspond to stages of development and certain intensities.