Earl made landfall on the Florida panhandle as a category 1 hurricane on
the Saffir/Simpson Hurricane Scale (SSHS), resulting in significant
storm surge flooding in the "Big Bend" area of Florida.
a. Synoptic History
Hurricane Earl formed from a strong tropical wave that
emerged from the west coast of Africa on 17 August. Persistent convection accompanied the wave as
it moved westward across the tropical Atlantic. A weak surface cyclonic circulation was
suggested in animation of satellite imagery, as well as in limited aircraft
reconnaissance and island reports as the system passed through the Lesser Antilles on
23 August. Tropical cyclone development appears to have been
inhibited while the system moved through the Caribbean by unfavorable winds aloft. These unfavorable
conditions were a result of the upper-level outflow from large and powerful
Hurricane Bonnie located over the southwest North Atlantic and moving
toward the North Carolina coast. Nevertheless, the tropical wave continued to be easily tracked
in satellite imagery as it moved into the Gulf of Mexico where cloudiness and
thunderstorms increased. The post-analysis "best track" in
Figure 1 (39K GIF) shows that the system became a
tropical depression over the southwest Gulf of Mexico midway
between Merida and Tampico, Mexico at 1200 UTC 31 August. Best track position,
central pressure and maximum one-minute sustained wind speed are listed for every
six hours in Table 1.
The tropical depression became Tropical Storm
Earl while centered about 500 n mi south-southwest of New Orleans, Louisiana near 1800 UTC 31 August based
on aircraft reconnaissance data. The center remained difficult to
locate by satellite, and, in fact, multiple centers were reported by aircraft reconnaissance for the
next couple of days. Occasionally, a new center would appear to form which made tracking
extremely difficult. Although the best track shown in Figure 1 (39K GIF)
indicates a general motion toward the north and then northeast near 10 knots while Earl was over the Gulf
of Mexico, a certain amount of "smoothing" was necessary to account for the multiple
centers and any possible center reformations.
Based on aircraft reconnaissance data, Earl is estimated to have reached
hurricane
status at 1200 UTC 2 September while centered about 125 n mi south-southeast of
New Orleans, Louisiana. The system never exhibited a classical hurricane appearance.
Instead, satellite imagery showed the deepest convection confined primarily to the
eastern quadrants of the circulation and aircraft reconnaissance data indicated a very
asymmetric wind field with the strongest winds located well east and southeast of the
center.
After briefly reaching category 2 status on the SSHS,
Earl made landfall near Panama City, Florida as a category 1 hurricane near 0600 UTC 3 September.
The strongest winds remained well to the east and southeast of the center which resulted in the
highest storm surge values in the Big Bend area of Florida, well away from the center.
The tropical cyclone weakened to below hurricane strength soon after making landfall,
and became extratropical at 1800 UTC 3 September while moving northeastward
through Georgia. The deepest convection became well removed from the center by
this time and the strongest winds were located over the Atlantic waters off the U.S.
southeast coast. The extratropical cyclone moved off the mid Atlantic coast near 1800
UTC 4 September, crossed over Newfoundland on 6 September and was tracked across
the North Atlantic until being absorbed by a larger extratropical cyclone (formerly
Hurricane Danielle) on 8 September.
b. Meteorological Statistics
Figures 2 (13K GIF) and
3 (14K GIF) show the curves of minimum central sea-level pressure
and maximum one-minute surface wind speed, respectively, as a function of time. The observations
on which the curves are based are also plotted and consist of aircraft reconnaissance
data and Dvorak-technique estimates using satellite imagery,
as well as synoptic "fixes" from surface data after landfall.
The operational aircraft reconnaissance flights into Earl were provided by the
U.S. Air Force Reserves. The minimum central pressure
reported by aircraft was 985 mb at 0045 UTC 3 September. This minimum pressure was measured by dropsonde
and was the lowest pressure reported during Earl's existence. The maximum winds of 104
knots from a flight level of 850 mb (near 5,000 feet) were measured at 1638 UTC 2
September. These peak winds were in a limited area about 80 n mi east of the center.
The
Hurricane Hunters
never reported an eyewall.
Reconnaissance data and land-based radar presentations suggest the hurricane weakened before moving onshore.
Satellite estimates underestimated the intensity of Earl, likely due to the fact that Earl
never exhibited a classical tropical cyclone pattern. For example, the maximum winds
estimated from the Tropical Analysis and Forecast Branch (TAFB), the tropical
branch of the Air Force Weather Agency
(AFGWC in figures) and the Synoptic
Analysis Branch (SAB) were 55 knots, 55 knots
and 45 knots, respectively.
The WSR-88D (Weather Surveillance Radar - 1988 Doppler) at
Slidell, Louisiana,
Mobile, Alabama,
Eglin Air Force Base, Florida and Tallahassee, Florida were
helpful in locating the center and areas of strongest winds aloft as the cyclone moved
near shore.
As is often the case in landfalling hurricanes, there were no reports from land stations
of sustained hurricane force winds in Earl. Table 2 lists selected U.S. surface
observations. The NOAA C-MAN station at Cape San Blas (near Apalachicola,
Florida) reported 10-minute sustained winds of 48 knots between 0400 and
0500 UTC and gusts to 61 knots at 0436 UTC 3 September. The strongest winds
at the time of landfall likely remained over water near the Big Bend area of Florida.
Several wind reports from north Florida were relayed to the NHC through amateur
radio volunteers. The highest measured wind gust was 79 knots at an
elevation of 33 feet from a Davis wind instrument located in the middle of St. George Island
at 29.40N 84.53W at 0102 UTC 3 September. Although these measurements are very much
desired to supplement the more official observations, they will not be listed in Table
2 unless their accuracy can be verified.
Storm surge was estimated to be near 8 feet in Franklin,
Wakulla, Jefferson and Taylor Counties and approximately 6 to 7 feet in Dixie County. These values
tapered off to between 2 to 3 feet in Lee County.
Rainfall totals of three to six inches were common near the path of Earl,
although much higher amounts were recorded in a few areas. A storm total of 16.38 inches near
Panama City, Florida, was the highest reported.
Several tornadoes were reported in central and north Florida, Georgia,
and South Carolina.
A rather extensive sampling of the Gulf of Mexico with GPS dropwindsondes by the
NOAA jet, centered around 0000 UTC 2 September,
showed a mid-level trough extending into the central Gulf which provided the steering currents
that moved Earl northeastward into the Florida panhandle.
c. Casualty and Damage Statistics
Hurricane Earl was directly responsible for three deaths. Two deaths occurred
as a result of a boat being capsized off Panama City. One death occurred as a result of a
tornado near St. Helena, South Carolina.
The Property Claim Services Division of the American Insurance Services Group
estimates that Earl caused insured property damage of $ 15 million in Florida, $ 1
million in Georgia, and $ 2 million in South Carolina. These estimates do not include
storm surge damage. In addition, the National Flood Insurance Program reported
$21.5 million of insured (storm surge related) losses in Florida. A conservative ratio
between total damage and insured property damage, compared to past landfalling
hurricanes, is two to one. Therefore, the total U.S. damage estimate is $ 79 million.
d. Forecast and Warning Critique
Several forecast difficulties were encountered during the life of Earl. As already
stated, the center was very difficult to locate by satellite and aircraft reconnaissance
continued to report multiple centers. Various computer models showed more than the
usual scatter in track forecasts. For example, the 72 hour model forecasts initiated
about a day and a half before landfall predicted that the center would be located
anywhere from the northwest Gulf of Mexico (Navy NOGAPS), to northern Arkansas
(BAMD), to northern Mississippi (GFDL), to over the Atlantic southeast of Cape Cod (LBAR).
In addition, 36 hours before landfall, most computer models
incorrectly showed a landfall somewhere in Louisiana. The BAMD, BAMM and the GFDI
(interpolated version of the
Geophysical Fluid Dynamics Laboratory model)
provided the best guidance in terms of the lowest average track forecast errors at 48 hours.
During Earl's life as a tropical storm or hurricane, the average official track
forecast errors were 84 n mi at 12 hours (10 cases), 156 n mi at 24 hours (8 cases), 261 n mi at
36 hours (8 cases) and 296 n mi at 48 hours (4 cases). These errors are considerably
larger than the previous ten-year averages of the official track errors.
The NHC intensity forecasts showed a negative bias (i.e., intensity was
underestimated), but most NHC intensity forecast errors were 15 knots or less prior to
landfall. Initial intensity forecasts correctly indicated that Earl would strengthen into
a hurricane.
Table 3 lists the various watches and warnings that were issued.
Since the NHC forecasts are based, in part, on the computer guidance,
hurricane warnings were not
issued with as much lead time as the NHC desires. Fortunately, appropriate
preparations appear to have been completed anyway.
Acknowledgments
Some of the information in this report was provided by NWS offices in the
Southern Region and is greatly appreciated.
Table 3. Watch and warning summary, Hurricane Earl, September 1998.
Date/time
(UTC) | Action | Location |
| 01/2100 | hurricane warning issued |
Pascagoula, MS to Cameron, LA |
| hurricane watch issued | east of Pascagoula, MS to Destin, FL |
| hurricane watch issued | west of Cameron, LA to High Island, TX |
| 02/0300 | tropical storm warning issued |
east of Pascagoula, MS to Destin, FL |
| 02/0900 | hurricane watch and warning discontinued |
west of Morgan City, LA |
| hurricane warning extended eastward | Pascagoula, MS to Destin, FL |
| tropical storm warning issued | east of Destin, FL to Apalachicola, FL |
| tropical storm watch issued | west of Morgan City, LA to Cameron, LA |
| 02/1300 | hurricane warning extended eastward |
Destin, FL to mouth of the Suwannee River, FL |
| watches and warning discontinued | west of Pascagoula, MS |
| tropical storm warning issued |
south of the mouth of the Suwannee River, FL to the Anclote Keys, FL |
| 02/1700 |
hurricane watch and tropical storm warning |
west of Pascagoula, MS to Grand Isle, LA including New Orleans |
| 03/0300 | watches and warnings discontinued |
west of the AL/FL state line |
| 03/0900 | hurricane warning discontinued |
Panama City, FL westward |
| 03/1500 | hurricane and tropical storm warnings discontinued |
remainder of Gulf coast |
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