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
Tropical Storm Henriette
4 - 8 September 2001
Henriette was a tropical storm most noteworthy for the manner of
its demise - a circumnavigation of, and ultimate absorption by
a. Synoptic History
(longitude vs. time) diagram of satellite images indicates that
Henriette's precursor was a tropical wave that crossed Central
America on 28-29 August. In a monsoon-like environment
characterized by large-scale low-level cyclonic turning, the wave
began showing signs of development a couple hundred miles south of
Acapulco, Mexico on 1 September, and by 2 September, convection had
become organized enough to warrant Dvorak classifications. A
QuikSCAT pass suggests that a closed circulation may have been
present by about 1200 UTC 3 September; however, visible satellite
images showed that the circulation was exposed northeast of the
poorly organized deep convection due to strong easterly or
northeasterly shear. Little change in organization occurred during
the next 24 hours as the system moved west-northwest a few hundred
miles south of Mexico.
Early morning visible satellite images on 4
September revealed a partially exposed but well defined low-level
circulation. While deep convection was confined to the southwestern
half of the circulation, the convection was close enough to the
center for Dvorak satellite intensity estimates to increase to
25-30 kt, and the system became Tropical Depression Nine-E at 1200
UTC 4 September, about 300 n mi west-southwest of
Manzanillo, Mexico, and also about 765 n mi east of Tropical
Depression Eight-E (which was to become Hurricane Gil).
The "best track" chart of the tropical
cyclone's path is given in Figure 1, with the wind and pressure
histories shown in Figure 2 and Figure 3,
respectively. The best track
positions and intensities are listed in Table 1.
A mid-level ridge to the north of the depression
took the system initially on a west-northwesterly track at about 14
kt. Early on 5 September, as the depression's heading turned to the
west, the separation between the circulation center and the deep
convection lessened and Dvorak satellite intensity estimates
increased to 35 kt. A QuikSCAT pass at 1347 UTC showed a surge of
southwesterly winds of 40-45 kt as far as 250 n mi south of the
center. On the basis of the Dvorak estimates and the QuikSCAT data,
it is estimated that the depression became Tropical Storm Henriette
at 0600 UTC 5 September, about 350 n mi south-southwest of Cabo San
Lucas, Mexico. At this time, Tropical Storm Gil was located about
690 n mi to the west of Henriette.
Henriette slowly became better organized on 6 September. The
convective pattern became more symmetric and the intensity
increased to 50 kt. Meanwhile, Henriette turned to the northwest
and accelerated to a forward speed of 15-17 kt as it began to feel
the influence of Hurricane Gil, then located 465 n mi to the
southwest. Upper-level easterly flow, which was still evident over
the cyclone early on the 6th, lessened and a more
favorable outflow pattern began to develop. Convective banding near
the center became better defined, and Henriette reached its peak
intensity of 55 kt at 0000 UTC 7 September.
At the time of peak intensity, water temperatures under
Henriette were about 25C but were rapidly-decreasing as the cyclone
moved northwestward. Within a few hours, the convective cloud tops
warmed significantly. As the convection collapsed, Henriette began
to weaken and turned west-northwestward around the periphery of
Hurricane Gil. At this point Gil, which had been moving westward,
turned sharply north-northwestward, and the distance between the
two cyclones began to decrease rapidly. By 0000 UTC 8 September,
Henriette was over 22C water, devoid of deep convection, and moving
westward at 20 kt about 330 n mi north of Hurricane Gil. Henriette
turned to the southwest at a speed of about 22 kt, and by 1200 UTC
8 September had weakened to a tropical depression. Well entrained
into the circulation of Gil, Henriette dissipated as a tropical
cyclone when it lost its own closed low-level circulation, as
evidenced by low-cloud trajectories, shortly after 1200 UTC on the
8th. At the time of dissipation, Henriette was located
about 210 n mi west of Tropical Storm Gil.
A low-cloud swirl, associated with the remnant vorticity of
Henriette, could be tracked for over 24 h after the tropical
cyclone formally dissipated. The swirl completed a cyclonic loop of
Gil, and could be tracked until about 1600 UTC 9 September, when it
was about 185 n mi north-northeast of Gil. The
tracks of both cyclones are shown in Figure 4,
and a satellite image
of the two systems is shown in Figure 5.
In the 52 h period beginning
at 1200 UTC 7 September, and ending when Henriette had been
completely absorbed, the pair executed a complete mutual
revolution. It is also apparent that the centroid of the two
systems was moving on a generally west-northwesterly track. The
closest approach appears to have occurred within an hour or two of
0600 UTC 9 September, when the two vorticity centers were separated
by about 90 n mi.
b. Meteorological Statistics
Observations in Henriette (Figure 2 and Figure 3)
included satellite-based 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). The highest Dvorak intensity estimate for Henriette was 55
kt, and this value is the peak intensity assigned to the tropical
A QuikSCAT overpass on 5 September showing 40-45 kt
winds well away from the center was the basis for the operational
upgrade of Henriette to a tropical storm. A QuikSCAT pass near 0300
UTC 8 September suggested that Henriette no longer had a closed
circulation, so it is possible that the cyclone may have dissipated
earlier than indicated in the best track.
There were no ship reports of winds of tropical storm
force associated with Henriette.
c. Casualty and Damage Statistics
There were no reports of damage or casualties
associated with Henriette.
d. Forecast and Warning Critique
Track forecasts for Henriette were quite good, given
the complicated synoptic environment. Average official track errors
(with the number of cases in parentheses) for Henriette were 32
(11), 63 (9), 87 (7), 128 (5), and 253 (1) n mi for the 12, 24, 36,
48, and 72 h forecasts, respectively. These errors are comparable
to the average official track errors for the 10-yr period 1991-2000
(Table 2), despite the fact that CLIPER errors for Henriette were
much larger than the long-term CLIPER errors. Barotropic models
were good performers, while the global multilayer models,
particularly the NOGAPS and UKMET, did not handle the interaction
between Henriette and Gil as well.
Henriette's intensity was also well-forecast. Average
official intensity errors were 6, 8, 10, 11, and 0 kt for the 12,
24, 36, 48, and 72 h forecasts, respectively. For comparison, the
average official intensity errors over the 10-yr period 1991-2000
are 7, 12, 16, 19, and 21 kt, respectively.
There were no watches and warnings associated with
Table 1: Best track for Tropical Storm Henriette, 4 - 8 September 2001.
|Lat. (°N)||Lon. (°W)
|04 / 1200||16.9||108.8||1006||25||tropical depression
|04 / 1800||17.5||110.1||1006||25||"
|05 / 0000||17.8||111.5||1006||30||"
|05 / 0600||17.9||112.9||1005||35||tropical storm
|05 / 1200||17.8||114.3||1005||40||"
|05 / 1800||17.7||115.7||1003||40||"
|06 / 0000||17.7||117.1||1000||45||"
|06 / 0600||18.2||118.5||997||50||"
|06 / 1200||18.8||119.9||997||50||"
|06 / 1800||19.6||121.5||997||50||"
|07 / 0000||20.5||122.9||994||55||"
|07 / 0600||21.3||124.5||997||50||"
|07 / 1200||22.1||126.0||1000||45||"
|07 / 1800||22.6||127.7||1000||45||"
|08 / 0000||22.9||129.8||1002||40||"
|08 / 0600||22.6||132.2||1004||35||"
|08 / 1200||21.6||134.3||1010||30||tropical depression
|08 / 1800||dissipated within circulation of
|07 / 0000||20.5||122.9||994||55||minimum pressure
Table 2: Preliminary track forecast evaluation for Tropical Storm Henriette - heterogeneous sample. Errors in nautical miles for
tropical storm and hurricane stages with number of forecasts in
parentheses. Bold numbers represent forecasts which were
better than the official forecast.
|Forecast Technique||Period (hours)
|CLIP||53 (11)||111 (9)||174 (7)||238 (5)||329 (1)
|GFDI||72 (10)||132 (8)||210 (6)||344 (3)||
|LBAR||50 (11)||79 (9)||84 (7)||69 (5)||243 (1)
|AVNI||58 (10)||93 (8)||138 (6)||127 (3)||
|BAMD||50 (11)||83 (9)||94 (7)||95 (5)||238 (1)
|BAMM||51(11)||81 (9)||93 (7)||85 (5)||87 (1)
|BAMS||52 (11)||80 (9)||93 (7)||86 (5)||73 (1)
|NGPI||105 (11)||210 (9)||339 (7)||483 (5)||
|UKMI||67 (4)||200 (4)||537 (4)||482 (2)||952 (1)
|GUNS||70 (3)||115 (3)||242 (3)||358 (1)||
|NHC Official||32 (11)||63 (9)||87 (7)||128 (5)||253 (1)
|NHC Official (1991-2000 mean)||37 (2273)||68 (2034)||99 (1802)||128 (1584)||185 (1203)
|*Output from these models was unavailable at time of forecast issuance.
positions for Tropical Storm Henriette, 4-8 September 2001.
maximum sustained surface wind speed curve for Tropical Storm
Henriette, 4-8 September 2001, and the observations on which the
best track curve is based.
minimum central pressure curve for Tropical Storm Henriette, 4-8
September 2001, and the observations on which the best track curve
Tracks of Tropical Storm Henriette and its
remnants (solid line) and Hurricane Gil (dashed line) for the
period 6-9 September 2001. The track of Henriette follows the
low-level vorticity center after dissipation. The double-headed
arrow indicates the center positions at their closest approach,
roughly 0600 UTC on the 9th.
Visible satellite image of Tropical
Storm Gil and the remnant cloud swirl of Tropical Storm Henriette,
at 1800 UTC 8 September 2001. Henriette is located to the southwest
of Gil. Image courtesy of the Naval Research