Hurricane Hugo, Puerto Rico, the Virgin Islands, and Charleston, South Carolina, September 17-22, 1989 (1994) / Chapter Skim
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Meteorology
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From page 172... ...
at the North Charleston Navy Yard. A reconstruction of the surface windfield at landfall suggests that the maximum sustained surface winds over land were 105 knots (121 mph)
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From page 173... ...
of 966 mb, with maximum sustained (Oman average) surface winds (V~)
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From page 174... ...
Surface observation sites are indicated by NWS, FAA, or NDBC call letters. Offshore locations A, B, C refer to airborne Doppler-radar wind profiles in Figure 9-8.
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From page 175... ...
The NHC endeavors to issue warnings with sufficient daylight time to allow preparations to be completed before tropical storm conditions arrive. The range of track-forecast-guidance products available to the forecasters from data collected at this time is shown in Figure 9-4 from Aberson and DeMaria (personal communication, 1990~.
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From page 176... ...
The marine advisories convey track and intensity forecasts to public officials and the media. Marine advisories issued at 1500 and 1800 EDT on September 21 contained postIandfall track forecasts that positioned Hugo about 35 mi west of Raleigh, North Carolina, by 0800 EDT on September 22; in fact, Hugo passed 115 mi to the west of Raleigh.
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From page 177... ...
INTENSITY PREDICTION While much is being learned about motion and track prediction that should lead to improved forecasts in the future, little is known about prediction of intensity changes, especially rapid intensification. In the 6-hour period from 1400 to 2000 EDT on September 2l, Hurricane Hugo intensified rapidly, with the MSEP deepening from 944 (category 3)
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From page 178... ...
5 200 - 190 - 180 - 170 12 13 14 15 16 17 18 19 20 21 22 SEPTEMBER 160 150 140 130 ~ 120 — 110 _ 100 cn -90 Z -80 70 Z sn 50 40 30 20 FIGURE 9~ Time series of 850-200 mb level wind shear evaluated from 400 800 km away from Hugo and intensity as measured by estimated maximum sustained surface-wind speed. Source: NOAA/HAD.
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From page 179... ...
WIND MEASUREMENTS BY RECONNAISSANCE AIRCRAFT Prior to and during landfall, NHC relies on reconnaissance aircraft to report observations of the location, strength, and intensity of the storm. These data are transmitted to NHC in real time in the form of "vortex messages," which also supply the maximum wind speed observed during a particular transit through the storm.
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From page 180... ...
updrafts and downdrafts greatly influence the wind profile and horizontal w~ndfields. Because of safely restrictions, it is often necessary to fly reconnaissance aircraft at levels higher than where the maximum winds might be found.
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From page 181... ...
. Based on the information available to NHC forecasters, and considering that the level of maximum winds was probably located below the aircraft between 500 and 2,000 m, the public advisories adequately warned the public of the maximum sustained winds to be expected on the coast.
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From page 182... ...
Storm total rainfall from Beaufort to Charleston ranged between 6 and ~ inches, dropping off to 2 inches near Myrtle Beach. Storm rainfall caused no serious flooding problems, although a subsequent rainfall episode (not associated with Hugo)
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From page 183... ...
for various storm intensities and approach categories determined by runs of the SLOSH mode} at NHC. At present, near-real-time forecasts of maximum storm surge are incorporated in the public advisories based on model runs encompassing a variety of possible landfall locations and storm intensities to account for forecast uncertainty (Sheets, 1990~.
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From page 184... ...
It is unknown exactly what were the actual maximum sustained surface winds in Hugo because no surface-wind measurements were made in the region where reconnaissance aircraft had measured peak wind speeds just prior to landfall. NHC advisories estimated VmsS winds of Il7 knots (135 mph)
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From page 185... ...
Note that the maximum winds observed by the aircraft were in the eyewall above the Bull Bay area about 25 mi northeast of Charleston. Within the Il7-knot (34-mph)
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From page 186... ...
. Lack of data in this region prevented observation of the region of maximum winds located in the southwest end of BuD Bay.
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From page 187... ...
In the cases where an anemometer trace was available, a I~ or 15-min average was estimated visually. The scale of wind features resolved by the measurements is a function of wind speed and averaging time and can be interpreted as the length of a sampling volume of air, as presented In Figure 9-13 Tom Powell (1990~.
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From page 188... ...
Overwater comparisons with the 3 CMAN stations and one ship indicated that the relationship between surface and flight-levl! wind was stabilit~y-dependent, with ratios of 90 to 100 percent over warm water off Savannah, Gal, on the weak side of the storm, and only 66 percent over cooler water at Frying Pan Shoals, offshore from Myrtle Beach, on the strong side of the storm.
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From page 189... ...
Public advisories at this time suggested that sustained hurricane-force winds extended 140 my east of the center and up to 50 my to the west. Based on these analyses, it would appear that a substantial portion of the warned coastline did not receive hurricane-force winds, although transient winds of hurricane force could have occurred.
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From page 190... ...
Setting up instrumentation safely and properly would require highly trained personnel to begin 24 to 48 hours before projected landfall in order to establish positions along a large enough portion of the coastline to account for possible forecast errors. Since the mean landfall-point error at 24 hours is approximately 56 mi, a portion of the coast twice this distance would have to be instrumented at a spacing of 9 to 12 me in order to resolve the region of maximum winds.
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From page 191... ...
In INS, HRD assisted in deploying a van to Texas for documentation of outer rainbands in Hurricane Gilbert. It should be pointed out that the NEXRAD planned by the NWS will be able to provide important information in remote areas near the levels of maximum winds, 0.5 to 2.0 km, but will not provide surface wind measurements because of limitations in beam geometry.
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From page 192... ...
A time series of radar reflectivity (proportional to rainfall intensity) , lO-min means, and peak gusts within each TO-niin period for Shaw AFB (Figure 9-17)
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From page 193... ...
, peak gusts (solid line) , and 15-min mean winds (dashed line)
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From page 194... ...
indicates that Hugo maintained a narrow, crescent-shaped region of 39 to 47 knots (45 to 54 mph) winds on the north side of the storm center and a secondary wind maximum 105 my to the southeast.
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From page 195... ...
at the middle of Bull Bay to 70 knots (80 mph) at Hickory, North Carolina As the storm decays after landfall, some mention of possible gusts should be included in the public advisories, to warn the public of the potential threat, even though sustained winds of less than hurricane force are being experienced.
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From page 196... ...
FUJITA DAMAGE DIRECTIONS \ \: ~ C,, _'\ W30 \\ 32 ~ 1 /1 11 \15$ 1 31 83 82 81 80 79 78 \50 Humcane Hugo FIGURE 9-19 Envelope of peak gusts relative to the track of Hugo's wind center. Superimposed are damage vector directions as determined by aerial surveys conducted by Fujita (1990~.
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From page 197... ...
Three hours after landfall, Hugo's maximum sustained surface winds decreased to below hurricane force (i.e., less than 58 knots [67 mph]
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From page 198... ...
Emergency response officials in inland communities should take necessary precautions when they are within the error margin of a postiandfall hurricane track forecast. Recommendation 10.
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From page 199... ...
1984. Airborne stepped frequency microwave radiometer measurements of rainfall rate and surface wind speed in hurricanes.
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From page 200... ...
1990. The landfall of Hurricane Hugo in the Carolinas: Surface wind distribution.
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From page 201... ...
1987. Operational airborne remote sensing of wind speeds in hurricanes.
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