Leslie was a short-lived tropical storm that developed from Subtropical
Depression One off the east coast of Florida, and subsequently moved
northeastward over the western Atlantic. Although neither Leslie nor the
subtropical depression was responsible for any damage or casualties, a
precursor disturbance combined with a stalled frontal boundary to produce
very heavy rainfall, and flood damage estimated at $700 million in southeast
Florida on 2-3 October. Three deaths in south Florida were indirectly
attributable to the flooding.
a. Synoptic History
The immediate precursor to Tropical Storm Leslie was a subtropical
depression that had formed inland near the east coast of central Florida at
1200 UTC 4 October. Ironically, the disturbance that led to the subtropical
cyclone was a tropical wave that entered the eastern Caribbean Sea on 27
September. Although its signature in satellite imagery was extremely weak
prior to this point, this was likely the same tropical wave that spawned
Hurricane Isaac.
Upon entering the Caribbean Sea, the wave was accompanied by disorganized
and sporadic thunderstorm activity over northern sections of South America.
On 29 September, the tropical wave and accompanying thunderstorm activity
moved north-northwest off the coast of Columbia into the central Caribbean
Sea. For the next two days, the disorganized cluster of thunderstorms moved
to the north-northwest around the circulation of Hurricane Keith, which at
that time was located in the northwest Caribbean Sea. By 1200 UTC 2
October, a distinct mid-level circulation was evident in satellite imagery
just south of western Cuba, near the Isle of Youth. This circulation moved
northward across western Cuba and the Straits of Florida, and by 1200 UTC 3
October it entered the extreme southeast Gulf of Mexico. Dvorak satellite
classifications by the Tropical Analysis and Forecast Branch (TAFB) and the
Satellite Analysis Branch (SAB) began at 0600 UTC on the 3rd.
Satellite and radar images showed a large area of showers and thunderstorms
that extended east of the mid-level circulation center from the Florida
Straits northward across the Florida Keys into extreme south Florida.
During the early afternoon of 3 October, a NOAA reconnaissance aircraft
investigated the disturbance in the southeast Gulf of Mexico, and found an
elongated trough of low pressure at a flight-level of 1500 ft but no
well-defined surface circulation center.
As the disturbance moved north towards the west coast of Florida, it
interacted with a stalled frontal boundary across southern Florida. During
the afternoon and evening of 3 October, a band of very heavy rainfall became
stationary across southeast Florida. Widespread rainfall, with
accumulations of 12 to 18 inches, occurred in a swath extending from
southwest Miami-Dade county to extreme southeast Broward County, and two
(F0) tornadoes touched down in Miami-Dade County.
After 0000 UTC 4 October, the mid-level circulation began moving northeast
and passed near Sarasota, Florida around 0600 UTC; however, the associated
shower and thunderstorm activity remained well southeast of the disturbance
in the frontal trough. Surface observations show the remnants of the
frontal trough remaining over south Florida for several hours after the
passage of the mid-level circulation center. They also show that by 1200 UTC
on the 4th, as the mid-level center continued northeastward over
central Florida, an associated well-defined surface low and circulation
developed just east of Orlando. At this time the convection was still
located well southeast of the surface low, with the strongest winds
approximately 150 nm from the center. Given this structure, as well as the
presence of a nearby upper-level short wave trough that may have assisted in
the development, the system at this stage is considered to have been a
subtropical depression.
At 1800 UTC on the 4th, the depression moved just offshore near
Daytona Beach, Florida (at which point it received a subtropical cyclone
classification, ST 1.5, by TAFB). Reconnaissance data at this time
confirmed that the strongest flight level winds (30 to 35 kt) remained well
southeast of the center. Subtropical Depression One moved slightly north of
east at 8 kt overnight, and early-morning satellite imagery on the
5th suggested that the low-level center was located closer to the
deep convection. Reconnaissance data near 1200 UTC 5 October confirmed that
the wind field had contracted, and that the maximum flight-level winds (44
kt) were within 75 nm of the center. On this basis Subtropical Depression
One was upgraded to Tropical Storm Leslie, about 200 n mi east of St.
Augustine, Florida. The "best track" chart of the cyclone's path, including
the subtropical stage, is given in
Figure 1, with the wind and pressure
histories shown in Figure 2 and
Figure 3, respectively. The best track is listed in
Table 1.
Leslie remained a weak tropical storm as it moved to the east-northeast on
the 5th, briefly threatened Bermuda but turned to the northeast
early on the 7th and passed about 250 miles to the west of the
island. The circulation of Leslie began to elongate and became entangled
with a cold frontal boundary, and the cyclone became extratropical by 1800
UTC on the 7th, when it was about 325 n mi north-northwest of
Bermuda. The remnant extratropical low moved rapidly northeastward,
crossing Newfoundland late on the 8th, and was tracked for another
day or so as it raced east-northeastward across the North Atlantic.
b. Meteorological Statistics
Observations in Leslie (Figure 2 and
Figure 3) include satellite-based Dvorak
technique intensity estimates from TAFB, SAB, and the U. S. Air Force Weather
Agency (AFWA). In addition, flight-level observations are available from
flights of the 53rd Weather Reconnaissance Squadron of the U.S.
Air Force Reserve Command and from the NOAA Aircraft Operations Center.
At 0000 UTC on the 6th, ship 8PNK reported winds of
36 kt about 60 n mi southeast of Leslie. There were no land-based reports
of tropical storm force winds. At 1800 UTC on the 7th
(at the time of extratropical transition), ship PDHW, about
200 n mi southeast of the center, reported winds of 33 kt.
No significant rainfall amounts are associated directly with either
Subtropical Depression One or Tropical Storm Leslie. The interaction of the
antecedent disturbance with the frontal trough over south Florida, however,
produced a number of rainfall storm totals in excess of 15 inches for
the 48 h period ending 7 AM EDT October 4th. These include
17.50 inches in South Miami, 15.79 inches at the Miami Weather Forecast
Office (near Sweetwater), and 15.30 inches at Miami International Airport.
Casualty and Damage Statistics
There were no reports of damage or casualties associated with either
Subtropical Depression One or Leslie. The interaction of the antecedent
disturbance with the frontal trough over south Florida, however, resulted in
damage estimated at $700 million, $500 million of which were agricultural
losses, and three deaths indirectly attributable to the flooding, two from
drowning as a result of driving vehicles into deep water, and one from a fall.
c. Forecast and Warning Critique
Leslie was a tropical storm for only two days. The average official track
errors for Leslie (with the number of cases in parentheses) were 54 (7), 113
(5), 132 (3), and 171(1) n mi for the 12, 24, 36, and 48 h forecasts,
respectively. These errors are mostly greater than the average official
track errors for the 10-yr period 1990-1999 (46, 85, 122, and 158 n mi,
respectively). Intensity forecasts for Leslie, which called for only modest
strengthening, were quite good.
Table 2 lists the watches and warnings associated
with Leslie. A tropical storm watch and warning were briefly in effect for
Bermuda before Leslie turned to the northeast and passed well west of the
island.
Table 1.
Best track for Tropical Storm Leslie, 4-7 October 2000.
Date/Time (UTC) | Position |
Pressure (mb) |
Wind Speed (kt) | Stage |
Lat. (°N) | Lon. (°W) |
04 / 1200 | 29.0 | 81.4 | 1012 | 30 | subtropical depression |
04 / 1800 | 29.5 | 80.8 | 1012 | 30 | " |
05 / 0000 | 29.7 | 79.9 | 1010 | 30 | " |
05 / 0600 | 29.8 | 78.6 | 1010 | 30 | " |
05 / 1200 | 29.9 | 77.3 | 1009 | 35 | tropical storm |
05 / 1800 | 30.2 | 75.9 | 1009 | 35 | " |
06 / 0000 | 30.3 | 74.3 | 1010 | 35 | " |
06 / 0600 | 30.6 | 73.1 | 1006 | 40 | " |
06 / 1200 | 30.9 | 72.4 | 1007 | 40 | " |
06 / 1800 | 31.3 | 71.8 | 1007 | 40 | " |
07 / 0000 | 32.1 | 70.7 | 1006 | 40 | " |
07 / 0600 | 33.1 | 69.6 | 1006 | 40 | " |
07 / 1200 | 35.4 | 68.3 | 1006 | 40 | " |
07 / 1800 | 37.4 | 66.7 | 1005 | 40 | extratropical |
08 / 0000 | 40.0 | 64.0 | 1004 | 40 | " |
08 / 0600 | 43.0 | 60.0 | 1003 | 40 | " |
08 / 1200 | 46.0 | 57.0 | 1003 | 40 | " |
08 / 1800 | 49.0 | 54.0 | 1005 | 35 | " |
09 / 0000 | 51.0 | 50.0 | 1007 | 35 | " |
09 / 0600 | 53.0 | 46.0 | 1006 | 35 | " |
09 / 1200 | 55.0 | 41.0 | 1005 | 35 | " |
09 / 1800 | 56.0 | 36.0 | 1003 | 35 | " |
10 / 0000 | 56.0 | 30.0 | 999 | 40 | " |
10 / 0600 | 55.0 | 24.0 | 987 | 50 | " |
10 / 1200 | 54.0 | 17.0 | 980 | 55 | " |
10 / 1800 | 53.0 | 10.0 | 973 | 60 | " |
|
06 / 0600 | 30.6 | 73.1 | 1006 | 40 | minimum pressure |
Table 2.
Watch and warning summary for Tropical Storm Leslie, 4-7 October 2000.
Date/Time (UTC) |
Action |
Location |
06 / 0300 | Tropical Storm Watch issued | Bermuda |
06 / 0900 | Tropical Storm Warning issued | Bermuda |
06 / 2100 | Tropical Storm Warning discontinued | Bermuda |
Figure 1.
Best track positions for Tropical Storm Leslie, 4-7 October 2000. Track
during the extratropical stage is based on analyses from the NOAA Marine
Prediction Center.
Figure 2.
Best track maximum sustained surface wind speed curve for Tropical Storm
Leslie, 4-7 October 2000, and the observations on which the best track curve
is based. Aircraft observations have been adjusted for elevation using 90%,
80%, and 85% reduction factors for observations from 700 mb, 850 mb, and
1500 ft, respectively. Estimates during the extratropical stage are based
on analyses from the NOAA Marine Prediction Center.
Figure 3.
Best track minimum central pressure curve for Tropical Storm Leslie, 4-7
October 2000, and the observations on which the best track curve is based.
Estimates during the extratropical stage are based on analyses from the NOAA
Marine Prediction Center.