Allison was an early season
hurricane
that formed over the northwest Caribbean Sea, the typical genesis area for
tropical cyclones in June.
It weakened to slightly below hurricane strength just before making landfall in north Florida.
Allison was responsible for one death (in western Cuba).
a. Synoptic History
Satellite images and rawinsonde data show that a tropical wave
passed over the Windward Islands on 28 May. When the wave entered the western Caribbean Sea on 1 June,
it was accompanied by a broad mid-level cyclonic circulation, which rawinsonde observations indicated
was particularly distinct at 700 mb. Convective cloudiness acquired sufficient organization to warrant
an initial Dvorak satellite classification at 0000
UTC 2 June. At that time, the cloud cluster was located a few hundred miles to the east of Honduras.
The system moved north-northwestward, and gradually became better organized during the daylight hours
of the 2nd. The first reconnaissance flight into the area revealed that the system became a
tropical depression around 0000 UTC on 3 June, centered 230 n mi
east of Belize City. Table 1 lists the
best track, which is displayed in
Figs. 1a (118K GIF) and 1b.
(107K GIF)
Continuing on its north-northwestward heading, the cyclone
strengthened into Tropical Storm Allison at 1200 UTC
on the 3rd. The intensifying storm turned northward, and moved through the Yucatan Channel.
The storm deepened even though southwesterly upper-level winds were creating a
shearing environment. In fact, by 1200 UTC on the 4th, Allison became a
65-knot hurricane over
the southeast Gulf of Mexico, centered 240 n mi west of Key West. However, the strengthening
trend soon ceased and Allison never developed beyond minimal hurricane intensity. Moving
northward near 15 knots, Allison headed for the Florida panhandle.
Early on 5 June, as the system drew nearer to the coast, it turned northeastward, and
weakened slightly, apparently in response to south-southwesterly vertical shear. Allison's
winds dropped just below hurricane force by 0600 UTC 5 June. Landfall occurred at 1400 UTC 5
June on the coast of north Florida, near Alligator Point, and again (after a very brief time
over water) at 1500 UTC near Saint Marks. Maximum winds at landfall are estimated at
55-60 knots. The storm weakened further as it headed inland to Georgia,
but tropical storm force winds persisted over Apalachee Bay until 2100 UTC on the 5th.
Allison diminished to a tropical depression over southern Georgia by 0000 UTC 6 June.
By 0600 UTC on the 6th, the system acquired
extratropical characteristics as it interacted
with a warm frontal zone to the northeast. Gale force winds developed along the Georgia and
South Carolina coasts as the cyclone's isobaric pattern expanded and the pressure gradient
increased well east of the low center. During the day on the 6th, the low moved northeastward
over the coastal plain of the southeastern U.S., emerging into the Atlantic a little north of
Cape Hatteras just after 0000 UTC 7 June. The low, with an associated area of gale to storm
force winds over its southeastern semicircle, moved rapidly northeastward, skirting the eastern
shore of Nova Scotia on the 8th, as it headed for Newfoundland. After passing over
Newfoundland on the 9th, the gale center turned northward, and then north-northwestward,
crossing the Arctic Circle to the west of Greenland on the 11th.
b. Meteorological Statistics
Figures 2 and 3 (61K GIF) show the post-analysis
best track minimum central pressure and maximum one-minute wind speed
for Allison, respectively, versus time. These were derived from: 1)
U.S. Air Force Reserve Unit Hurricane Hunter
aircraft data; 2) analyses of satellite images, using the Dvorak technique,
performed by meteorologists at the
Synoptic Analysis Branch (SAB) and the
Tropical Analysis and Forecast Branch (TAFB, formerly the
Tropical Satellite Analysis and Forecast unit, TSAF, as in the figures)
and at the Air Force Global Weather Central (AFGWC);
and 3) surface reports (including analyses from synoptic charts).
The maximum wind speed recorded in Allison was 74 knots at 700 mb
from an
Air Force Hurricane Hunter
plane on 0019 UTC on 5 June.
The highest surface wind estimated by the aircraft crew was 65 knots. The highest
observed sustained (8-min) winds were reported from the
NOAA Data Buoy
42003, 52 knots. The minimum observed central pressure was 987 mb, from the
Hurricane Hunters,
at 1346, 1527, and 2224 UTC on
4 June. It is presumed that Allison was at its peak intensity at 1200 UTC 4 June, since this was
the only time that aerial reconnaissance data showed any kind of eye
structure (a partial wall cloud). The peak observed flight-level
winds at 850 mb were 69 knots around that time.
In Cuba, Allison produced winds of 40 to 45 knots in Pinar del Rio.
Stronger gusts, 55 knots, were reported at the weather service office in Havana.
Rainfall totals to as high as 18 inches were observed.
The highest reported wind speed observation in Florida was a gust to
50 knots at Cedar Key. A 1-minute sustained wind speed of
37 knots with a gust to 47 knots was observed at Turkey
Point. A 30-minute sustained wind speed of 35 knots with a gust to 49 knots
was measured at the St. George Island Causeway. A 1-minute sustained wind speed of
34 knots with a gust to 39 knots was observed at Apalachicola.
The outer rainbands of Allison spawned a number of tornadoes, waterspouts and funnel clouds.
A waterspout was sighted, at 2005 UTC 4 June, five miles east of Ponte Vedra Beach FL, moving
north. A probable tornado struck in eastern Polk County, FL, from 0245-0315 UTC 5 June; a
funnel cloud was spotted by two observers but no tornado was seen. However, 75 homes and
mobile homes near Haines City apparently received some damage, and trees were down and storage
sheds were damaged near West Lake Wales.
There were several tornadoes reported in the northeast Florida/southeast Georgia area on 5
June. A tornado at Jacksonville Beach in Duval County, FL, around 0738 UTC, downed power lines
and trees, flipped over two vehicles, and caused minor damage to fences and houses. A
northward-moving tornado was sighted over extreme northern Nassau County, FL, at 0810 UTC.
This twister moved over Saint Marys in Camden County, GA around 0420 UTC. Damage in Nassau
County was light, but heavier damage was incurred in Camden County, where an elementary school
in Saint Marys sustained building damage and facilities at the Kings Bay Naval Submarine Base
were damaged. Numerous trees were downed at the base as well. At 0930 UTC, a waterspout moved
onshore near Brunswick in Glynn County, GA, causing minor damage to structures.
From 0945-1000 UTC, waterspouts were sighted from Fernandina Beach in Nassau County, FL. A
funnel cloud with a possible brief touchdown took place at 1000 UTC near Everret City, also in
Glynn County, GA. Two tornado touchdowns occurred south of Brunswick, GA at 1045 UTC. A
tornado was reportedly sighted near Gainesville, Alachua County, FL at 1251 UTC. There was
also a possible tornado east of Interlachen in Putnam County, FL, around 1340 UTC.
Rainfall totals were generally between 4 and 6 inches near the path of Allison, from
Florida through North Carolina.
Storm surge heights of at least 6.8 feet above National
Geodetic Vertical Datum were measured in Apalachee Bay (Turkey Point). Maximum storm surge
heights were estimated at 6 to 8 ft from Wakulla through Dixie counties, 4 to 6 ft in Franklin
County, and 2 to 5 ft from Levy through Hillsborough Counties.
c. Casualty and Damage Statistics
Heavy rains caused the collapse of 32 structures in western Cuba. One person was killed and
three injured due to these collapses. Overall, economic losses were apparently not large.
In the U.S., there were no direct deaths due to Allison.
Damage was greatest in the coastal sections of Dixie, Levy,
Taylor and Wakulla counties, mainly from storm surge effects,
with 60 houses and businesses damaged. A house collapsed at
Bald Point in Franklin County. About 5000 people evacuated
from the coast. Other coastal effects included mostly minor
beach erosion, damage to sea walls and coastal roadways, and
the sinking of several small boats. Otherwise, minor wind
damage to roofs, signs, power lines and trees occurred over
most of the north Florida peninsula. Some relatively minor crop damage was also reported.
Total damage in Florida is estimated at $860,000, and the
tornado near St. Marys, Georgia, caused about $800,000 in
damage, bringing Allison's overall U.S. damage figure to $1.7 million.
d. Forecast and Warning Critique
Overall, the path of Allison was well forecast, but
initially there was a slow bias. Mean official track errors
were 35, 66, 100, 126, and 234 n mi at 12-, 24-, 36-, 48-, and
72-hours, respectively. All of these errors are between 21
and 35 per cent lower than the most recent ten-year means. In
general, the average official forecast errors were about equal
to, or smaller than, any of those from the objective track
models. The exception was at 72 hours, wherein the GFDI,
BAMD, and A90E models had mean errors that were 55, 44, and 41
n mi lower, respectively than the mean official forecast.
Allison's strengthening to a hurricane was not anticipated
because of the presence of southwesterly shear, and this necessitated
the upgrading of a tropical storm watch
to a hurricane warning. Landfall occurred
roughly at the center of the hurricane warning area.
Acknowledgements
Jim Lushine, at the
National Weather Service Office (NWSO) in Miami, Florida,
summarized damage and tornado reports. Al Sandrik at
NWSO, Jacksonville, also
provided information on tornadoes in Florida and Georgia.
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