TROPICAL CYCLONE REPORTS
Tropical Storm Barbara
Tropical Storm Cosme
Tropical Storm Erick
Tropical Depression Six-E
Tropical Storm Henriette
Tropical Storm Ivo
Tropical Storm Lorena
Tropical Depression Fourteen-E
Tropical Storm Manuel
Tropical Cyclone Report
26 August - 2 September 2001
Stacy R. Stewart
National Hurricane Center
27 October 2001
After a quick start to the season with a major hurricane in May,
Flossie became the third hurricane (category 2 on the
Saffir-Simpson Hurricane Scale) to develop in the northeastern
Pacific Ocean. It remained well offshore the west coast of Mexico
and was only a threat to marine interests.
a. Synoptic History
Flossie originated from a tropical wave that moved off the west
coast of Africa on 11 August. This wave initially spawned Atlantic
Tropical Storm Chantal on 14 August, about 1300 n mi east of the
southern Windward Islands. Chantal and the subsequent wave envelope
in which it was embedded continued to track rapidly westward at 20
to 25 kt across the tropical Atlantic and into the Caribbean
By 19 August, Chantal and the associated wave had slowed down
significantly as the system moved into the western Caribbean Sea.
Chantal eventually stalled along the east coast of the Yucatan
Peninsula late on 20 August. While Chantal remained
quasi-stationary near Chetumal, Mexico, the southern portion of the
wave crossed over Central America and emerged over the northeastern
Pacific Ocean south of Guatemala on 21 August, as indicated by
surface observations and QuikSCAT satellite-derived winds.
For the next two days, a pre-Flossie disturbance of cloudiness
and showers tracked westward parallel to the southwest coast of
Mexico and changed little in overall organization. On 23 August,
however, a closed surface circulation appeared in QuikSCAT imagery
(not shown). The associated convection was not particularly well
organized. The system tracked west-northwestward close to the
Mexican coast until 25 August. Later that day, outer convective
bands of the broad circulation moved onshore near Manzanillo,
Mexico, and produced wind gusts to tropical storm force. Satellite
classifications and QuikSCAT wind data, however, indicated that the
circulation was still too broad and disorganized to be classified
as a tropical depression.
By 0000 UTC 26 August, the pre-Flossie circulation had moved far
enough away from the negative influence of the Mexican coastal
mountains. The low-level circulation became better defined and deep
convection consolidated closer to the system center. Satellite
intensity estimates continued to increase and, by 0600 UTC, they
suggested that the system had developed into Tropical Depression
Seven-E about 235 n mi south-southeast of Baja California. The
"best track" chart of the tropical cyclone's path is given in
while the best track positions and intensities are listed in
Table 1. Wind and pressure plots are shown in
Figure 2 and Figure 3,
The depression tracked westward and convective organization
continued to improve during the day. At 1800 UTC, the cyclone
strengthened into Tropical Storm Flossie about 195 n mi south of
the southern tip of Baja California. Flossie continued to move
westward and passed about 7 n mi north of Socorro Island. By 1800
UTC 27 August, Flossie slowed from 9 kt down to 5 kt, and rapidly
intensified into a hurricane. The intensification process leveled
off when Flossie began to experience southwesterly shear while
interacting with an upper-level low pressure system located to the
west. Over the next 24 h, Flossie turned sharply southward and made
a small cyclonic loop about 200 n mi west of Socorro Island. The
sharp change in track motion was probably due to binary interaction
between Flossie and the upper-level low that moved cyclonically
around the south and east side of the hurricane before eventually
weakening and lifting out to the northeast. Once the upper-level
low and its negative shear effects moved away from Flossie, the
hurricane began to intensify again late on 28 August and eventually
peaked at 90 kt at 1800 UTC 29 August. Tropical Rainfall
Measurement Mission (TRMM) microwave satellite imagery
(Figure 4 and Figure 5)
indicated that Flossie had become significantly better organized
during an 18 h period with the eye decreasing to nearly half its
original size. Eye contraction often corresponds with rapid
intensification. However, an approaching mid-latitude trough began
to induce southwesterly upper-level shear on Flossie, disrupting a
possible rapid intensification process. Instead, Flossie began a
slow weakening trend while tracking northwestward for the next day
and a half and became a tropical storm again at 0600 UTC 31 August,
when it was located about 470 miles west of the southern tip of
Baja California. At 1800 UTC, the cyclone began moving over sharply
lower sea-surface temperatures, which helped to bring about its
rapid demise. Flossie weakened to a depression at 1200 UTC 1
September and completely dissipated later that day about 200 n mi
west of Punta Eugenia in western Baja California.
The remnant low-level circulation drifted slowly westward over
the northeastern Pacific Ocean as a swirl of low clouds for several
more days. The mid- to upper-level circulation moved rapidly
northeastward across northen Baja California before dissipating
over the desert region of the southwestern United States.
b. Meteorological Statistics
Observations in Flossie (Figure 2 and Figure 3)
Dvorak technique intensity estimates from the Tropical Analysis and
Forecast Branch (TAFB), the Satellite Analysis Branch (SAB) and the
U. S. Air Force Weather Agency (AFWA). Flossie's peak intensity of
90 kt at 1800 UTC on 29 August is based on a Dvorak satellite
classification of 90 kt (T5.0) from the TAFB.
There were no ship or surface reports of sustained tropical
storm force winds associated with Flossie. However, sustained winds
of 30 kt with gusts to 40 kt were reported in squalls at
Manzanillo, Mexico (MMZO) at 1645 UTC 25 August.
c. Casualty and Damage Statistics
The remnant moisture from Flossie helped to trigger strong
thunderstorms, deadly lightning, and flash floods across portions
of Southern California. While there were no directly-related deaths
or damage reported with Flossie when it was a tropical cyclone,
there were deaths due to lightning strikes reported in southwestern
California up to 36 h after Flossie had dissipated as a tropical
cyclone. Four people were struck by lightning in the San Diego and
San Bernardino Mountains on 2 and 3 September, and 2 of the 4
victims died. A 53-year old man was killed on 2 September when he
was struck in the head by lightning while hiking and a 13-year old
boy was also struck in the head and killed while standing in an
In addition, more than 2 inches of rain fell in one hour and
caused flash flooding in San Diego and Riverside Counties on 2-3
September. Strong downdraft winds also knocked down a tree onto a
house. Total damage from Flossie's remnants was estimated at
d. Forecast and Warning Critique
Average official track errors for Flossie were 30, 60, 94, 123, and 186 n mi for the 12, 24,
36, 48, and 72 h forecasts, respectively (Table 2). The number of
cases ranged from 21 at 12 h to 11 at 72 h. These errors are lower
than the average official track errors for the 10-year period
1991-2000 (37, 68, 99, 128, and 185 n mi, respectively), except at
72 h. While not included in the normal verification process, it is
worth noting that forecast errors during all stages (including the
tropical depression stage; number of cases indicated in
parentheses), were slightly lower at 30 (26), 59 (24), 91 (22), 121
(20), and 182 (16) at the same time periods, respectively. Higher
than average CLIPER errors, along with the best track plot
indicate that Flossie posed many forecast challenges. The NHC
official forecast, however, correctly captured the small cyclonic
loop and subsequent short-term southwesterly motion near Socorro
Island on 28 August. In fact, some of the smallest official
forecast (OFCL) errors occurred prior to and during this time of
erratic motion, whereas all of the NHC model guidance produced
large errors during this same period. The largest OFCL track errors
occurred toward the end of Flossie's lifetime when the system was
forecast to move slowly northwestward over colder water, while it
continued on a northerly track. The best performing NHC track
forecast guidance was the AVNI and GUNA models.
Average official intensity errors were 6, 8, 8, 10,
and 19 kt for the 12, 24, 36, 48, and 72 h forecasts, respectively.
This is slightly better than the average official intensity errors
over the 10-yr period 1991-2000 (7, 11, 14, 16, and 20 kt,
respectively). These errors were slightly better than the SHIPS
intensity model forecasts.
There were no watches or warnings associated with
Table 1: Best track for Hurricane Flossie, 26 August - 2 September 2001.
|Lat. (°N)||Lon. (°W)
|26 / 0600||19.1||108.5||1004||30||tropical depression
|26 / 1200||19.7||109.7||1004||30||"
|26 / 1800||20.0||110.6||1003||35||tropical storm
|27 / 0000||20.1||111.6||1002||40||"
|27 / 0600||20.2||112.5||1000||45||"
|27 / 1200||20.1||113.3||994||55||"
|27 / 1800||19.9||113.8||989||65||hurricane
|28 / 0000||19.5||114.1||989||65||"
|28 / 0600||19.2||114.3||989||65||"
|28 / 1200||19.1||114.3||985||70||"
|28 / 1800||19.4||114.7||985||70||"
|29 / 0000||19.8||115.1||983||75||"
|29 / 0600||20.1||115.4||980||80||"
|29 / 1200||20.6||116.2||977||85||"
|29 / 1800||20.9||116.6||972||90||"
|30 / 0000||21.5||117.1||975||85||"
|30 / 0600||21.9||117.7||979||80||"
|30 / 1200||22.4||118.0||983||70||"
|30 / 1800||22.9||118.1||987||65||"
|31 / 0000||23.4||118.4||989||65||"
|31 / 0600||23.6||118.6||994||60||tropical storm
|31 / 1200||23.9||118.9||997||55||"
|31 / 1800||24.3||119.2||999||50||"
|01 / 0000||24.8||119.3||1002||40||"
|01 / 0600||25.2||119.1||1005||35||"
|01 / 1200||25.6||118.9||1005||30||tropical depression
|01 / 1800||26.0||118.6||1006||30||"
|02 / 0000||26.6||118.4||1007||25||"
|02 / 0600||dissipated
|29 / 1800||20.9||116.6||972||90||minimum pressure
Table 2: Preliminary forecast evaluation (heterogeneous sample)
for Hurricane Flossie, 26 August - 2 September
2001. Forecast errors for tropical storm and hurricane
stages (n mi) are followed by the number of forecasts in
parentheses. Errors smaller than the NHC official forecast are
shown in bold-face type.
|Forecast Technique||Period (hours)
|CLIP||34 (21)||78 (19)||127 (17)||175 (15)||262 (11)
|GFDI||31 (21)||67 (19)||110 (17)||165 (15)||288 (11)
|GFNI||43 (20)||84 (18)||128 (16)||172 (14)||292 (10)
|LBAR||36 (21)||79 (19)||124 (17)||167 (15)||276 (11)
|AVNI||33 (20)||68 (19)||102 (17)||128 (15)||141 (9)
|BAMD||33 (21)||67 (19)||97 (17)||125 (15)||193 (11)
|BAMM||35 (21)||78 (19)||134 (17)||197 (15)||305 (11)
|BAMS||37 (21)||75 (19)||129 (17)||194 (15)||320 (11)
|NGPI||48 (21)||95 (19)||132 (17)||173 (15)||268 (11)
|UKMI||33 (20)||63 (19)||103 (17)||138 (15)||218 (11)
|GUNS#||33 (20)||64 (19)||96 (17)||127 (15)||210 (11)
|GUNA#||31 (20)||63 (19)||91 (17)||118 (15)||166 (9)
|NHC Official||30 (21)||60 (19)||94 (17)||123 (15)||186 (11)
|NHC Official (1991-2000 mean)||37 (2273)||68 (1835)||99 (1646)||128 (1475)||185 (1187)
|*Output from these models was unavailable at time of forecast issuance.
#GUNS is the GFDI-UKMI-NGPI model
ensemble average and GUNA is the GFDI-UKMI-NGPI-AVNI model ensemble
Best track for Hurricane Flossie, 26 August - 2 September 2001.
Best track maximum sustained surface wind speed curve for
Hurricane Flossie, 26 August - 2 September 2001, and the observations on
which the best track curve is based.
Best track minimum central pressure curve for Hurricane Flossie,
26 August - 2 September 2001, and the observations on
which the best track curve is based.
Flossie near 75 kt intensity (0200 UTC 29 Aug 2001) with a partial eyewall
indicated in the TRMM microwave channels (lower-left and lower-right
panels), whereas no eye feature is indicated in conventional infrared
imagery (upper-left and upper-right panels). Image is courtesy of the Naval
Hurricane Flossie at peak intensity of 90 kt (1831 UTC 29 Aug 2001). Note
the small (less than 10 n mi) diameter eye in the 85 GHz composite data
(lower-right panel). The eye is more distnict and is almost half the size
it was 18 h earlier as seen in Figure 4. Image is courtesy of the
Naval Research Laboratory.