The Re-analysis of Hurricane Andrew (1992)

Submission to the NHC Best Track Change Committee

1 August 2002

Abstract:

This document proposes a set of revisions to the intensity portion of the "best track" for 1992's Hurricane Andrew, which is currently classified as a Saffir-Simpson Category 4 hurricane at its landfalls at Eleuthera Island, Bahamas and in South Florida, USA. The revisions would make Andrew a Category 5 hurricane at both landfalls, with a Florida landfall intensity of 145 kt. The peak intensity of Andrew is assessed to be 150 kt at 1800 UTC 23 August.

Introduction:

This proposed revision is part of "The Atlantic Hurricane Database (HURDAT) Re-analysis Project" (NOAA/NASA Grant #GC02-093) that the author is Principal Investigator for (Landsea et al. 2002). While Hurricane Andrew would have been examined sequentially in this project sometime in 2005, a request was made by the Tropical Prediction Center Director Max Mayfield to expedite Andrew's re-analysis because of the massive societal impacts that the hurricane caused not only in South Florida, but nationwide. For example, insurance costs for residential homes have dramatically increased in the years since 1992 for residents of Southeast Florida as a direct result of this single hurricane and today it is extremely difficult to obtain coverage from a private insurer. Additionally, we are at the point now where credible evidence from new meteorological studies has called into question the original estimation of Hurricane Andrew's intensity and that these new conclusions are not likely to be significantly advanced and/or altered in the next two years of the Re-analysis Project. It is crucial that an accurate as possible account be provided as to the characteristics of all tropical cyclones and Hurricane Andrew in particular, since society needs reliable information on the frequency and intensity of past catastrophic events to best plan for the future.

Best Track Changes:

No changes are proposed for the track of Hurricane Andrew (Fig. 1), which formed in the tropical North Atlantic, moved west-northwestward then westward crossing the northern Bahamas and South Florida into the Gulf of Mexico before making final landfall over Louisiana and decaying over the Southeast United States during the period 17 to 28 August, 1992. The proposed new wind history is given in Fig. 2 and Table 1 with alterations for the dates of 22 to 26 August; no changes are proposed to the best track pressure data (Fig. 3). (Winds from Atlantic basin tropical cyclones are recorded in HURDAT in six-hourly intervals as the maximum sustained [1 min] surface [10 m] windspeed somewhere in the circulation of the tropical cyclone.) The original wind best track is shown in Fig. 4. The revisions make Andrew a Category 5 hurricane on the Saffir-Simpson Hurricane Scale (Saffir 1973, Simpson 1974) at landfall in both Eleuthera Island, Bahamas and in South Florida, with a Florida landfall intensity of 145 kt (originally 125 kt). The peak intensity of Andrew is assessed to be 150 kt (originally 135 kt) at 1800 UTC 23 August. The remainder of this report provides justification for these changes along with appropriate references.

Flight level wind extrapolation to the surface:

Studies by two independent groups - Franklin et al. (2002) and Dunion et al. (2002)/Dunion and Powell (2002) - provide strong evidence that the methodology used to estimate the maximum sustained surface wind in Hurricane Andrew (Rappaport 1994; Mayfield et al. 1994; Powell and Houston 1996) was too conservative for a good portion (~5 days) of its lifetime. This new understanding of the wind structure in strong hurricanes is due to an advance in technology - the Global Positioning System (GPS) dropwindsonde - that allowed for the first time a detailed look at the wind profile in a hurricane's eyewall from flight level to the ocean's surface. These unique new observations, first collected in Hurricane Guillermo in 1997, suggest that all hurricanes in the aircraft reconnaissance era including Hurricane Andrew should be re-examined for their intensity when the primary method for estimating surface winds were from flight-level winds extrapolated to the surface.

Franklin et al. (2002) examined several hundred GPS dropwindsonde profiles in the hurricane eyewall and have shown that the mean ratio of surface to 700 mb winds was about 91.5% in the eyewall region. However, because there was an effort to preferentially seek out the surface wind maximum at the expense of the flight-level maximum, this ratio may not be quite appropriate for estimating the peak surface wind from the peak flight-level wind. Therefore, a separate analysis was conducted at the flight-level RMW. At the flight-level RMW (FL-RMW), the mean surface to 700 mb wind speed ratio was in fact a bit lower, 88%. Since sondes dropped at the flight-
level RMW encounter the peak flight-level wind but not the peak surface wind, the 88% ratio should represent a lower bound on the mean ratio of peak surface winds to peak 700 mb winds, if azimuthal variation is ignored. There does exist some variability of the mean adjustment ratio with azimuth, but this variability does not change the recommended adjustment factors. The strongest FL winds are generally found on the right-hand side of the storm. The eyewall sondes show that the adjustment factor in the right quadrant is a little lower than in the left quadrant (0.891 vs. 0.928, for all eyewall sondes). Assuming this difference is applicable at the FL-RMW, a more accurate lower bound mean adjustment factor for the right quadrant FL-RMW would be just above 86%. The upper bound on the mean adjustment factor for the right quadrant would be just under 90%.

Recent work by Dunion et al. (2002) and Dunion and Powell (2002) also support a revised flight-
level to surface wind extrapolation in the context of the H*WIND surface wind analyses of tropical cyclones (Powell et al. 1996, 1998) due of the new GPS dropwindsonde observations. Dunion et al./Dunion and Powell utilized the drop data to alter the H*WIND analysis in a two-
step process. First, analyses of the dropwindsondes shows that the assumption previously in H*WIND that 700 mb flight-level data were equivalent to a mean boundary layer (0 to 500 m) was an underestimation of the true boundary layer winds. Secondly, the GPS dropwindsondes showed that the surface to mean boundary layer wind ratio reached a minimum near 100 to 110 kt mean boundary layer winds and had an increasing ratio with stronger winds, in contrast to a steadily decreasing ratio with stronger boundary layer winds previously utilized in H*WIND. The combined effect of these two changes to H*WIND produces maximum sustained surface winds for hurricanes with aircraft reconnaissance data at 700 mb substantially higher (10-20%) than the earlier version. This new H*WIND methodology provides surface wind analyses (from extrapolated flight-level wind observations) that agree within 5% of the Franklin et al. (2002) new estimates for major hurricanes.

Consequently, unless there is other information to the contrary, current operational practice at the National Hurricane Center (Franklin et al. 2001) is to assess the intensity of a hurricane at about 90% of the peak wind observed at the 700 mb level. This factor is at the high end of the range established by the sondes (86%-90%), in part due to a simple rounding of the midpoint of this range, but also to account for the likelihood that the highest 700 mb wind speed was not sampled.

About an hour prior to Andrew's landfall in South Florida, at 0810Z Air Force reconnaissance aircraft measured a 10-s wind at 700 mb of 162 kt, 90% of which is 146 kt. Ten-second flight-
level winds are customarily assumed to represent 1-min sustained winds in the inner core of hurricanes. One-minute averaging of the flight-level winds would tend to underestimate the true maximum 1-min wind because the aircraft does not remain in the peak gradient region that long on a radial flight track, especially in relatively small hurricanes like Andrew. Peak 10-s flight level winds supporting Category 5 at the surface (at least 136 kt) were found in three consecutive minute observations (0809, 0810, and 0811Z) using the Franklin et al. [2002] adjustment of 90%. The 1-min mean flight-level wind at 0810 was 159 kt, or 143 kt when adjusted to the surface using 90%. Neither were these the only aircraft obs that support Category 5 winds; a later 10-s report (over land, at 0918Z) yields 138 kt using the same reduction. The 1-min mean aircraft wind at 0918Z was 149 kt, which reduces to 134 kt using 90%. (However, it is not known what the wind profile and surface winds are for conditions well-inland, since the vast majority of GPS dropwindsondes were dropped over the open ocean. It would not be appropriate to claim that these winds at 0918Z provided good evidence for maximum sustained surface winds of Category 5 conditions at that time.) Lacking compelling contradictory data, the flight-level observations would be accepted as representative and a hurricane presenting these data today would almost surely be assigned an operational intensity of about 145 kt, well above the threshold for Category 5 hurricane conditions.

Analyses from the revised H*WIND surface wind analysis system (Dunion and Powell 2002) provide a surface wind estimate of 150 kt from the 0810Z reconnaissance flight-level data, which is a 93% surface to flight-level ratio (Figure 5). This is in good agreement with the Franklin et al. (2002) estimate, perhaps not surprisingly since they are both based upon new formulations from the nearly the same set of GPS dropwindsondes.

After the time of the 162 kt aircraft report, Andrew's central pressure continued to fall up to and just after landfall, perhaps by as much as 10 mb. It is quite possible that flight-level winds at the time of landfall were even higher than what was observed earlier.

It has been suggested that applying the 90% rule to the flight-level data may be inconsistent with available surface data in Hurricane Andrew, in particular the Fowey Rocks and R. Fairbanks observations. The Fowey Rocks C-MAN weather station reported a peak 2 min wind of 122 kt at an elevation of 40 m, which adjusts to about 111 kt for a maximum 1 min surface [10 m] wind. R. Fairbanks, an amateur weather observer, noted a peak gust of 184 kt from his home-based anemometer, which adjusts to a maximum 1 min surface wind of about 119 kt after accounting for an overestimation bias of his instrument and a typical gust factor [Rappaport 1994; Mayfield et al.1994, Powell et al. 1996]. While Fowey Rock station reported windspeed and direction until its failure around 0800Z, the Fairbanks observation has no wind direction associated with it and only an approximate time (0830 to 0900Z). Both of these platforms likely failed before the strongest winds of Andrew arrived, as they were in the northwest portion of the eyewall outside of the radius of maximum winds while the peak winds were closer to the storm's center in the northern portion of the eyewall. (The Fairbank observation may instead have been in the north eyewall, but its storm-relative location at the time of the peak gust in very uncertain.) Thus both of these observations do not represent the maximum sustained winds of Hurricane Andrew at landfall in South Florida. Inspection of these surface observations in comparison with reduced-
to-the- surface flight level data do not suggest any large inconsistency, though it is difficult to directly compare them for two reasons. First, the flight level data primarily were in radial legs running north-south and east-west, which did not coincide well spatially with the Fowey Rocks and Fairbanks observations. Secondly, because of the turbulent and transient nature of hurricane wind field, it is not straightforward generally to make direct comparisons from a storm-relative perspective the adjusted flight-level winds to the couple of observations available. It would take a systematic discrepancy over many observation points to warrant a departure from the mean relationship. This does not appear to be the case in Andrew's landfall in South Florida.

Assuming that the 162 kt aircraft wind is representative of the peak winds present at 700 mb, a surface adjustment factor of 83% or less is required to keep Andrew a Category 4 hurricane. Of the hurricanes examined in Franklin et al. (2002), only Bonnie, a weakly convective storm with a large eyewall, has been observed to have a mean ratio that low. If the surface winds are kept at 125 kt, this implies an adjustment factor of 77%. No storm has yet been observed to have a mean adjustment factor this low. Furthermore, although sample sizes tend to get small when the dropwindsonde sample gets stratified, there does appear to be enhanced relative surface winds when the winds are very high (Dunion et al. 2002, Franklin et al. 2002), and when vertical motions are particularly vigorous (Franklin et al. 2002). Andrew at landfall in South Florida would have satisfied both of these conditions. In other words, there is very little evidence to conclude to that Andrew had a lower than normal adjustment factor.

Winds in HURDAT for Hurricane Andrew are also altered, as is seen in Table 1 and Figures 2 and 4, for the dates of 22 to 26 August based upon the Franklin et al. (2002) methodology, which has been found to be consistent with the work of Dunion et al. (2002) and Dunion and Powell (2002). These changes are appropriate given that aircraft reconnaissance observations were available throughout this period and there were very few surface observations that were likely indicative of the maximum sustained surface winds.

Radar reflective cell track data:

Low-altitude radar cell tracking suggests surface winds similar to those implied by the flight-
level data. Recently, some vectors based on cell tracking from the Miami WSR-57 radar in and inside of Andrew's eyewall just prior to landfall in south Florida have been generated (P. Dodge, personal communication). Low-altitude radar cell tracks have been demonstrated to provide winds in the circulation of a hurricane that are comparable to measured winds from aircraft to within 10% (Tuttle and Gall 1999). The two highest cell motions found were 176 kt (91 m/s) at 400 m at 0839Z and 180 kt (93 m/s) at 1100 m at 0730Z (Figs. 6 and 7). If we assume that the maximum wind in the eyewall near the boundary layer top (BLT) was 178 kt, we can adjust this wind to the surface using mean dropsonde profiles. If we use the overall eyewall mean profile from Franklin et al. (2002) to go from the BLT to the surface (75%), we get a surface-adjusted wind of 134 kt, just shy of Category 5. However, as mentioned above, there is an apparent relationship between boundary layer adjustment factors and wind speed, with adjustment factors increasing with wind speed once the BLT speed exceeds about 105 kt (Fig. 12 of Franklin et al. 2002). Franklin et al suggest that the surface to BLT adjustment factor increases to 82% for BLT wind speeds of 135-155 kt (this is their highest category). Using this adjustment, the BLT wind of 178 kt converts to 146 kt at the surface. The Dunion and Powell (2002) methodology also suggest that these low-altitude radar cell tracks correspond to winds of 151 kt at the surface. Thus these new radar-derived data for Hurricane Andrew provide additional evidence for increasing the intensity of the storm near the South Florida coast to Category 5 status.

Pressure-wind relationships:

Andrew's South Florida landfall pressure of 922 mb corresponds to a wind of 139 kt (Category 5), using the operational (Dvorak) pressure-wind relationship (OFCM 2002). The regionally-
based pressure-wind relationships developed by Landsea et al. (2002) suggest 133 kt for the southerly (25o N and equatorward) and 122 kt for the subtropical (25 to 35o N) relationships. Tropical cyclones with a small radius of maximum wind (RMW) will tend to have higher winds for the same central pressure than large storms. Andrew's surface RMW in the north eyewall was only about 9 nmi based upon the peak storm surge location, substantially smaller than the 14 nmi climatologically for a central pressure of 922 mb and a latitudinal position of 25o N (Vickery et al. 2000). Additionally, Andrew was imbedded in a stronger than usual surface ridge. Typically at Andrew's position in August, climatology is for sea level pressures of around 1017 mb, while the environmental pressure at Andrew's landfall was about 1020 mb. This would also somewhat enhance the pressure gradient and thus the peak winds in the storm. Thus given Andrew's small size and the higher than usual surrounding pressure, its 922 mb central pressure does support maximum sustained surface winds of about 145 kt at landfall. These proposed revisions to Andrew's best track fall within the range of existing scatter in the operational pressure-wind relationship (Fig 8, Brown and Franklin 2002). The current best track pressure-
wind pair at landfall (922 mb-125 kt) also falls within the observed scatter around the operational pressure wind curve; however, it is near the edge on the light-wind (left) side of the curve. A storm of Andrew's size and structure should not be this far to the left of the pressure-wind curve. Thus the central pressure of Andrew at landfall, allowing for its smaller than typical size and higher than normal environmental pressures, strongly supports increasing the intensity of the storm near the South Florida coast to Category 5 status.

Satellite estimates of intensity:

The proposed peak wind for the South Florida landfall is 20 kt above the operational Dvorak (1984) estimates. However, the proposed points fall within the envelope of previously observed scatter, as 10% of all Dvorak intensity estimates are in error by 20 kt or more (Brown and Franklin 2002). More importantly, Dvorak estimates of Andrew's intensity were consistently too weak, as can be seen in Fig 3. Beginning at 0000Z on the 23rd, measured reconnaissance pressures were running 10-15 mb lower than the Dvorak estimates. Dvorak pressure estimates remained consistently too weak until after the Florida landfall. Given this, as well as the likelihood of Andrew's winds exceeding the Dvorak pressure-wind expectation because of Andrew's size as discussed above, the Dvorak wind estimates for Andrew cannot reasonably be expected to yield an accurate intensity estimate.

Recently a retrospective objective Dvorak technique (ODT - Velden et al. 1998) analysis for Andrew was run (C. Velden, personal communication). The ODT shows an intensity spike (T6.7) at 0900Z (Table 2) corresponding to winds increasing by over 30 kt to 132 kt in a short period of time, in good agreement with the pressure tendency after the last reconnaissance pressure. However, because the oblique look-angle associated with single GOES operations in 1992 which would give an eye temperature cooler than what would have been measured directly overhead, the ODT value provided is likely an underestimate of the true intensity (C. Velden, personal communication). Thus given the systematic bias of the operational Dvorak technique to underestimate the intensity of Andrew and the new analysis from the objective Dvorak technique, satellite-based intensity estimates of Hurricane Andrew at South Florida landfall are consistent with an assessment of Category 5 intensity.

Consistency with SLOSH model runs:

The first run of the Sea, Lake, and Overland Surge from Hurricanes (SLOSH - Jelesnianski et al. 1992) for a simulation of Andrew's impact shown in Powell and Houston (1996) utilized a pressure difference of 87 mb between the eye and the periphery, an RMW of 8 nmi, and an 8 m/s motion of the storm. SLOSH-derived maximum sustained surface winds of about 125 kt helped produce a storm tide of 15.2 feet. While this original SLOSH run was unable to obtain the peak storm tide observed (16.9 feet), it also significantly overestimated the storm tide outside of the peak area. These biases are likely due to a pressure gradient/wind field that is not sufficiently concentrated in the eyewall (B. Jarvinen, personal communication). A newer version of SLOSH can run with forcing from an observationally-based wind field (J. Chen and W. Shaffer, personal communication). Using the H*WIND output with maximum sustained surface winds of 150 kt based upon the GPS dropwindsonde parameterizations, this newer version of SLOSH does give a more realistic 15.8 foot storm tide, but at the expense of having an even larger overestimation bias outside of the peak wind and storm tide region. It is possible that the new wind analysis from H*WIND is utilizing a RMW that is somewhat too large (11 nmi) and a dropoff in the winds outside of the peak wind region that is too weak (B. Jarvinen, personal communication). Thus while the current configuration of SLOSH has difficulties replicating the details of a storm tide of a very small hurricane like Andrew, these runs of SLOSH suggests that an intensity of 145 kt maximum 1 min sustained surface winds (Category 5) at landfall for Hurricane Andrew in South Florida is reasonable.

Estimates of intensity from damage surveys:

Analyses of structural damage that occurred due to winds in Hurricane Andrew has been utilized to provide intensity estimates (Fujita 1992; Wakimoto and Black 1994). These identify two main regions of peak structural damage: a larger area in the Naranja Lakes neighborhood and a smaller area farther north in Cutler Ridge neighborhood near the peak storm tide region. While the Fujita analysis did not provide a numerical guide for his revised f-scale analysis, the Wakimoto and Black analysis suggests F3 conditions corresponding to peak gusts of 135 to 175 kt. Powell and Houston (1996) converted these to a range of 105 to 135 kt for a maximum 1 min sustained surface wind, utilizing a standard overland gust factor of 1.3. These values are in the Category 3 or 4 range for Andrew's landfall in South Florida

Another interpretation (P. Black, personal communication) is that these F3 damage regions were caused not by 2-5 s gusts, but a longer timescale feature because of the extended lateral extent - a few to several hundred meters - on the order of about 20 s. With a longer timescale, a factor of 1.12 is utilized to convert this to an approximate 1 min sustained surface wind, giving a range of 120 to 155 kt. These values would instead suggest Hurricane Andrew's impact in South Florida would be consistent with either a Category 4 or 5 hurricane.

Regardless of which timescale and gust factors are chosen to convert the F-scale values to a sustained wind, less weight is placed here upon these estimates of windspeed because of other factors besides the peak wind in contributing toward structural damage including variation in construction type and quality, "duration of strong winds, structural sensitivity to wind direction, local topographic effects, and subgrid-scale convective downdrafts or microbursts" (from Powell and Houston 1996). Indeed, the larger of the two F3 regions (Naranja Lakes) occurred well away from the location of the estimated maximum sustained surface winds via other methodologies. In this region, winds were first experienced from the southeast as the west eyewall went through and then the winds shifted to be from the northwest as the east eyewall passed overhead. It may very well be for this situation that the duration of winds and 180 degree shift in the wind direction has as much to do with the structural damage that occurred there as the peak wind itself.

Therefore, due to major uncertainties in the application of this methodology and the wide range of possible maximum sustained winds obtained, no firm conclusion can be made from this evidence except to say that either Category 4 or 5 is consistent with the structural damage caused by Hurricane Andrew's winds at landfall in South Florida.

Discussion of uncertainties:

The purpose of the National Hurricane Center Best Track Change Committee is to ensure the most accurate historical hurricane record possible, consistent with contemporary science. It has been suggested that the record in the case of Andrew should not be changed, in part because of the uncertainty surrounding the maximum wind, and an analogy has been made to the rules of instant replay in the NFL, where conclusive evidence is required to overturn an official's call. Such a standard seems inappropriate for this Committee's deliberations, though, and is inconsistent with the Committee's mission statement. No storm's intensity can be determined with complete accuracy; the surface observations are almost never sufficiently comprehensive, and indirect measures must always be used. Uncertainty in a wind speed estimate should not be an obstacle to revising an earlier estimate that is inconsistent with the observations, interpreted using current understanding.

It is acknowledged that the re-analysis presented here of Andrew's intensity at landfall in South Florida (and elsewhere in its lifetime) is not known with exact certainty, nor will it ever be. However, it is concluded here that Hurricane Andrew's true intensity is VERY LIKELY to be in the range of 136 to 155 kt (Category 5) for the maximum sustained surface winds at landfall in South Florida with a best single estimate of 145 kt and that it is quite UNLIKELY that it was a 125 kt (Category 4) as originally thought.

Acknowledgments:

This proposed revision is based upon substantial research that the author has only had a peripheral role in. In particular, thanks are primarily due to the recent research on the structure of the hurricane's inner core conducted by Mike Black, Jason Dunion, James Franklin, and Mark Powell. Their work has provided the key advance in our knowledge of hurricane that has allowing this re-analysis to take place. James Franklin also provided a writeup that served as much of the basis of the document found here. Peter Dodge is gratefully acknowledged for providing the "new" radar reflectivity-based cell track winds utilized in this study. Chris Velden also provided a retrospective objective Dvorak technique analysis for Hurricane Andrew that provided insight from the satellite intensity perspective. Brian Jarvinen provided a special run of the SLOSH model to assist in the analysis of Hurricane Andrew's intensity from a storm surge perspective. Kind suggestions and recommendations in this re-analysis were given by many people in addition to those mentioned above: Pete Black, William Bredemeyer, Steve Feuer, Paul Hebert, Charlie Neumann and Hugh Willoughby.

References:

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Dvorak, V.F., 1984: Tropical cyclone intensity analysis using satellite data. NOAA Technical Report. NESDIS 11, 47 pp.

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Franklin, J. L., M. L. Black, and K. Valde, 2002: GPS dropwindsonde wind profiles in hurricanes and their operational implications. Submitted to Wea. Forecasting.

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30.

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Landsea, C. W., C. Anderson, N. Charles, G. Clark, J. Dunion, J. Partagas, P. Hungerford, C. Neumann and M. Zimmer, 2002: The Atlantic hurricane database re-analysis project: Documentation for the 1851-1910 alterations and additions to the HURDAT database. Hurricanes and Typhoons: Past, Present and Future, R. J. Murnane and K.-B. Liu, Eds., Columbia University Press, in press.

Mayfield, M., L. Avila, and E. N. Rappaport, 1994: Atlantic hurricane season of 1992. Mon. Wea. Rev., 122, 517-538.

OFCM, 2002: National Hurricane Operations Plan. Office of the Federal Coordinator for Meteorological Services and Supporting Research (OFCM), FCM-P12-2002, Washington, D.C.

Powell, M. D., and S. H. Houston, 1996: Hurricane Andrew's landfall in South Florida. Part II: Surface wind fields and potential real-time applications. Wea. Forecasting, 11, 329-349.

Powell, M. D., S. H. Houston, L. R. Amat, and N. Morisseau-Leroy, 1998: The HRD real-time surface wind analysis system. J. of Wind Engng. and Indust. Aero., 77 & 78, 53-64.

Powell, M. D., S. H. Houston, and T. A. Reinhold, 1996: Hurricane Andrew's landfall in South Florida. Part I: Standardizing measurements for documentation of surface wind fields. Wea. Forecasting, 11, 304 - 328.

Rappaport, E. N., 1994: Hurricane Andrew. Weather, 49, 51-61,

Saffir, H. S., 1973: Hurricane wind and storm surge. The Military Engineer, 423, 4-5.

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Tuttle, J. And R. Gall, 1999: A single-radar technique for estimating the winds in tropical cyclones. Bull. Amer. Meteor. Soc., 80, 653-668.

Velden C. S., T. L. Olander, and R. M. Zehr, 1998: Development of an objective scheme to estimate tropical cyclone intensity from digital geostationary infrared imagery. Wea. Forecasting, 13, 172-186.

Vickery, P. J., P. F. Skerlj, and L. A. Twisdale, 2000: Simulation of hurricane risk in the U. S. using empirical track model. J. of Structural Engineering, 1222-1237.

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Chris Landsea

NOAA/AOML/HRD

Fig. 1 Track of Hurricane Andrew.

Table 1: Revisions in HURDAT and at landfall in the Bahamas and the United States for Hurricane 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, the original 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=4

54545 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 1010

54555 08/17*112 374 30 1009*117 396 30 1008*123 420 35 1006*131 442 35 1003

54560 08/18*136 462 40 1002*141 480 45 1001*146 499 45 1000*154 518 45 1000

54565 08/19*163 535 45 1001*172 553 45 1002*180 569 45 1005*188 583 45 1007

54570 08/20*198 593 40 1011*207 600 40 1013*217 607 40 1015*225 615 40 1014

54575 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 80 969

54580 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*254 758 135 922

54585 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*258 831 115 947

54590 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*278 896 120 941

54595 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 50 991

54600 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 25 999

54610 08/28*344 867 20 1000*354 840 20 1000* 0 0 0 0* 0 0 0 0

54615 HRCFL4BFL3 LA3

54615 HRCFL5BFL4 LA3

********

Table 1: Continued.

Landfall Data

Date/Time Lat Lon Max Saffir- Central Landfall States

Winds Simpson Pressure Location Affected

8/23/2100Z 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, BFL3

8/24/0905Z 25.5N 80.3W 145kt 5 922mb Homestead CFL5, BFL4

*** * **** ****

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

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

***

(Note that the maximum sustained winds indicated in the Landfall Data table are those that occurred somewhere in the storm circulation at the time that the center of the hurricane made landfall, not necessarily on land near or at the location listed. However, for the landfalls in South Florida and Louisiana, the winds indicated - 145 kt and 110 kt, respectively - are the also the winds estimated to have impacted the coasts as well. Thus the impact of Hurricane Andrew is assessed as a Saffir-
Simpson Category 5 at landfall in Southeast Florida and a Category 3 in Louisiana.)

Table 2.	Objective Dvorak intensity estimates for Andrew (C. Velden, personal communication).

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