Tropical Cyclone Report
Tropical Storm Grace
30 August - 2 September 2003
Stacy R. Stewart
National Hurricane Center 27 November 2003
Tropical Storm Grace was a short-lived tropical
cyclone that developed over the western Gulf of Mexico. Grace moved
inland along the upper Texas coast and produced little damage.
a. Synoptic History
A strong tropical wave, accompanied by a vigorous low
pressure system, moved off the west coast of Africa on 19 August.
Both conventional satellite data and QuikSCAT microwave wind data
indicated that the wave came close several times over the next few
days to developing into a tropical cyclone. Convection became most
pronounced on 21 August when some outer banding features and a
circular cirrus outflow pattern briefly developed. However, the
rapid westward motion, exceeding 20 kt at times, may have disrupted
the low-level circulation enough to prevent the convection from
becoming concentrated near the center. The system also moved
through a mid- to upper-level region of very dry air over the
central tropical Atlantic, and by late on 22 August nearly all of
the convection had dissipated.
As the pre-Grace wave continued its westward trek, a
second convective development phase occurred when the system slowed
as it moved across the Lesser Antilles on 24-25 August. However,
southwesterly upper-level shear ahead of a large upper-level trough
located to the west disrupted the development process. Devoid of
significant convection, the wave moved west-northwestward at 6-8 kt
until it reached the northwestern Caribbean Sea on 28 August, when
deep convection re-developed along the wave axis. When the tropical
wave crossed the northern Yucatan Peninsula on 29 August, a broad
low pressure area re-developed along the wave axis as it turned
northwestward toward the Texas coast. While there was an abundance
of deep convection associated with this system, the disturbance
remained poorly organized until later that day when satellite
classifications were initiated by the Tropical Analysis and
Forecast Branch (TAFB) and the Satellite Analysis Branch (SAB).
Convective organization continued to improve during
the early morning hours of 30 August, and surface observations in
conjunction with satellite intensity estimates indicated that
tropical Depression Eleven had formed about 290 n mi east-southeast
of Corpus Christi, Texas. 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.
The depression initially showed some signs of
interaction with an upper-level cold low, but this was short-lived
and subsequent reconnaissance flights indicated that the cyclone
was mostly tropical in nature. More specifically, a reconnaissance
flight at 2125 UTC 30 August indicated the depression had likely
strengthened into Tropical Storm Grace around 1800 UTC about 245 n
mi east-southeast of Corpus Christi, Texas. The upper-low situated
a few hundred miles to the west of Grace was forecast by most of
the various numerical models to move quickly westward. However,
this did not occur and, as a result, persistent southerly to
southwesterly upper-level shear prevented the deep convection from
organizing around the low-level circulation. While remaining broad
and somewhat disorganized, Grace moved northwestward on 31 August
at a faster forward speed of about 15 kt.
Due to the broad low-level inner wind field, it was
difficult to pinpoint the exact location of Grace in satellite
imagery and by reconnaissance aircraft. In addition, a large
surface high pressure system located over the southeastern United
States was strengthened the pressure gradient and the low-level
wind field for several hundred miles northeast of the center. Grace
was forecast to move inland in the vicinity of Corpus Christi,
Texas. However, the long fetch of strong southeasterly winds and
cyclonic shear, in conjunction with several bursts of deep
convection east of the original low-level center, may have caused
the spin up of a new center about 100 n mi farther to the north.
This new circulation center of Grace moved inland near San Luis
Pass, Texas on the southwestern tip of Galveston Island at 1100 UTC
31 August 2003 with 35-kt winds. The original circulation weakened
and eventually dissipated before it made landfall. Grace continued
to move northwestward and quickly weakened back to a tropical
depression shortly after making landfall. Tropical Depression Grace
turned northward over northeastern Texas on 1 September and merged
with a frontal zone near the Arkansas-Oklahoma border early on 2
September.
b. Meteorological Statistics
Observations in Tropical Storm Grace
(Figure 2 and Figure 3)
include 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), as well as flight-level and dropwindsonde observations from
flights of the 53rd Weather Reconnaissance Squadron of
the U. S. Air Force Reserve Command.
Two ships reported tropical storm force winds
associated with Grace. Several oil drilling platforms also observed
tropical storm force winds, but these measurements were made
several hundred feet above the surface. The ship and oil platform
reports of winds of tropical storm force associated with Grace are
given in Table 2. Selected surface observations from land stations
and data buoys are given in Table 3.
Grace's peak intensity of 35 kt was based on a blend
of a reconnaissance 1500 ft flight-level spot wind report of 43 kt,
which converts to a surface wind value of approximately 34 kt, and
two sustained 35-kt wind reports from the Sabine Pass (Sea Rim
State Park - SRST5), Texas C-MAN station at 1000 UTC and 1200 UTC
31 August 2003. The 35-kt surface wind reports at Sabine Pass were
also used to support the 35 kt intensity at landfall.
Maximum storm surge values were generally around 1-2
ft along the upper Texas coast, primarily on Galveston Island, and
produced minimal effects.
Rainfall totals across the Houston metropolitan area
and the upper Texas coast were in the 3 to 5 in range with some
isolated reports in excess of 9 in. Grace's relatively fast forward
speed of 10-15 kt during and after landfall helped to minimize the
heavy rainfall and flash flood threat typically associated with
landfalling tropical cyclones.
No tornadoes were reported.
c. Casualty and Damage Statistics
The main effect associated with Tropical Storm Grace
was isolated heavy rainfall and some inland freshwater floods
across the upper Texas coastal area, north of where the center of
Grace made landfall.
No deaths or casualties were reported in association
with Grace. No monetary damage figures are available and insured
losses did not meet the $25 million threshold in order to be
recorded by the American Insurance Services Group.
d. Forecast and Warning Critique
Average official track errors (with the number of
cases in parentheses) for Grace were 108 (5), 158 (5), 223 (5), and
305 (4) n mi for the 12, 24, 36, and 48 h forecasts,
respectively1.
These errors are much greater than the average official
track errors for the 10-yr period 1993-2002 of 45, 81, 116, and 150
(Table 4). The significance is minimized due to the number of cases
being small. The primary reason for the large official forecast
(OFCL) errors was the re-development of the low-level center much
farther north, near Galveston Island, where Grace eventually made
landfall (Fig. 4). The official forecast closely followed the
consensus of the interpolated GFDL, UKMET, NOGAPS, and GFS/AVN
(GFDI, UKMI, NGPI, and AVNI, known as GUNA) models, which also
performed poorly, and kept Grace farther south near Corpus Christi.
However, it is noteworthy to point out that the real-time
operational global models, AVNO, NGPS, and UKM (used to generate
the interpolated models), as well as the interpolated 10-member
GFS/AVN ensemble model, performed very well and correctly forecast
a more northward landfall, albeit in the Freeport-Matagorda area.
In contrast, the operational GFDL model performed rather poorly by
taking Grace inland over and south of Corpus Christi, which
resulted in a significant degradation in the GUNA consensus
forecasts. However, none of the NHC forecast models correctly
predicted the landfall on Galveston Island.
Average official intensity errors were 5, 15, 5, and
3 kt for the 12, 24, 36, and 48 h forecasts, respectively. For
comparison, the average official intensity errors over the 10-yr
period 1993-2002 are 6, 10, 13, and 15 kt, respectively. The higher
than average 24 h intensity error was due to some slight
intensification expected before. Instead, significant vertical
shear remained across the Grace throughout its lifetime while over
water.
Table 5 lists the watches and warnings associated
with Tropical Storm Grace.
Acknowledgments
Some of the data in this report was
furnished by National Weather Service Offices in Houston/Galveston
and Corpus Christi,
Texas.
1All forecast verifications in this report include the
depression stage of the cyclone. National Hurricane Center verifications
presented in these reports prior to 2003 did not include the depression
stage.
Table 1: Best track
for Tropical Storm Grace, 30 August - 2 September
2003.
Date/Time (UTC) | Position | Pressure (mb) | Wind Speed (kt) | Stage |
Lat. (°N) | Lon. (°W) |
30 / 1200 | 24.3 | 92.4 | 1008 | 30 | tropical depression |
30 / 1800 | 24.9 | 93.3 | 1009 | 35 | tropical storm |
31 / 0000 | 25.8 | 94.3 | 1009 | 35 | " |
31 / 0600 | 27.2 | 94.9 | 1008 | 35 | " |
31 / 1200 | 29.4 | 95.2 | 1007 | 35 | " |
31 / 1800 | 30.1 | 95.6 | 1009 | 30 | tropical depression |
01 / 0000 | 30.9 | 96.4 | 1009 | 25 | " |
01 / 0600 | 31.9 | 96.6 | 1010 | 20 | " |
01 / 1200 | 32.6 | 96.5 | 1010 | 20 | " |
01 / 1800 | 33.6 | 95.7 | 1011 | 20 | " |
02 / 0000 | 34.1 | 95.0 | 1011 | 15 | " |
02 / 0600 | 34.6 | 94.5 | 1013 | 15 | " |
02 / 1200 | | | | | merged with frontal zone |
31 / 1100 | 29.0 | 95.1 | 1007 | 35 | landfall near San Luis Pass, Texas |
31 / 1200 | 29.4 | 95.2 | 1007 | 35 | minimum pressure |
Table 2: Selected
ship and oil drilling platform reports with winds of at least 34 kt
for Tropical Storm Grace, 30 August - 2 September
2003.
Ship Name or Call Sign | Date/Time (UTC) | Lat. (°N) | Lon. (°W) | Wind dir/speed (deg/kt) | Pressure (mb) |
WZJC | 31/0000 | 27.6 | 91.8 | 130 / 36 | 1011.3 |
SHIP | 30/1500 | 26.8 | 91.25 | 150 / 40 G
50 | missing |
Oil Platforms | | | | | |
KQT8 (400
ft) | 31/0246 | 27.9 | 92.75 | 150/45 | 1011.8 |
KQT8 (400
ft) | 31/0345 | 27.9 | 92.75 | 150/35 | 1012.8 |
KQT9 (400
ft) | 31/1744 | 27.8 | 90.65 | 180/37 | 1016.2 |
KQT8 (400
ft) | 31/1749 | 27.9 | 92.75 | 160/34 | 1013.9 |
|
Table 3: Selected
surface observations for Tropical Storm Grace, 30 August - 2 September
2003.
| Minimum Sea-level Pressure | Maximum Surface Wind Speed (kt) | |
Location | Date/ Time (UTC) | Press. (mb) | Date/ Timea
(UTC) | Sust. Windb
(kts) | Peak Gust (kts) | Storm Surgec
(ft) | Storm Tided
(ft) | Rain (storm total) (in) |
Texas |
Alice Airport (KALI) | | | 31/2223 | | 26 | | | |
Baffin Bay - TCOON | 31/0000 | 1008.2 | 30/2200 | | 30 | | | |
Baytown - Hartman Brdg | | | | | | | | 3.98 |
Cedar Bayou - SH146 | | | | | | | | 3.50 |
Clear Creek - 2nd Outflow | | | | | | | | 5.40 |
Cleveland | | | | | | | | 4.62 |
Eagle Point | 31/1200 | 1007.9 | | | | | | |
East Matagorda Bay | | | 31/1200 | | 32 | | | |
Freeport | | | | | | | | 5.57 |
Galveston Airport (KGLS) | 31/1116 | 1008.5 | 31/0803 | 28 | 35 | | | 3.72 |
Galveston Buoy 42035 | | | 31/1300 | 26 | 33 | | | |
Galveston Pleasure Pier | 31/1200 | 1007.4 | 01/0900 | 26 | 33 | | | |
Galveston North Jetty | 31/1100 | 1007.4 | | | | | | |
Garwood (Colorado River) | | | | | | | | 3.40 |
Goodrich (W5QVK) | | | | | | | | 5.35 |
Goodrich
School | | | | | | | | 4.25 |
Horsepen Ck-Bay Ar Blvd | | | | | | | | 4.57 |
Houston Arpt (KHOU) | | | | | | | | 4.98 |
Houston Cedar Bayou | | | | | | | | 2.84 |
Houston Clr Ck - FM 528 | | | | | | | | 3.43 |
Houston Int'cntl (KIAH) | | | | | | | | 2.96 |
Huntsville ASOS (KUTS) | | | | | | | | 7.94 |
Jamaica Beach (JBHT2) | 31/1230 | 1008.2 | | | | | | 5.01 |
Jamaica Beach CO-OP | | | | | | | | 2.92 |
Kingsville NAS (KNQI) | | | 01/0057 | | 26 | | | |
League City (NWS) | | | | | | | | 7.13 |
Matagorda River Locks | | | | | | | | 9.00 |
McMullen Co. Airport | | | 31/2124 | | 26 | | | |
Nassau Bay - Clear Creek | | | | | | | | 5.90 |
New Caney | | | | | | | | 5.14 |
Onalaska | | | | | | | | 3.28 |
Onalaska (W5GRZ) | | | | | | | | 4.65 |
Pearland | | | | | | | | 6.47 |
Point Blank 6N | | | | | | | | 5.04 |
Port O'Connor | | | 30/2000 | | 26 | | | |
Seabrook (NASA Rd 1) | | | | | | | | 6.89 |
Sea Rim St. Park (SRST2) | | | 31/1220 | 35 | | | | |
Sea Rim St. Park (SRST2) | | | 31/1450 | 35 | | | | |
Sea Rim St. Park (SRST2) | | | 31/1444 | | 46 | | | |
West Bay (29.14N 95.15W) | 31/10001 | 1007.7 | | | | | | |
aDate/time is for sustained wind when both
sustained and gust are listed.
bExcept
as noted, sustained wind averaging periods for C-MAN and land-based
ASOS reports are 2 min; buoy averaging periods are 8
min.
cStorm
surge is water height above normal astronomical tide
level.
d Storm
tide is water height above National Geodetic Vertical Datum (1929
mean sea level).
1Minimum
pressure reported three times between 1000-1200UTC 31 July 2003. |
Table 4: Preliminary forecast evaluation (heterogeneous sample) for Tropical
Storm Grace, 30
August-2 September 2003. Forecast errors (n
mi) are followed by
the number of forecasts in parentheses. Errors smaller than the NHC
official forecast are shown in bold-face
type. Verification
includes the depression stage, but does not include the
extratropical stage, if any.
Forecast Technique | Period (hours) |
12 | 24 | 36 | 48 | 72 | 96 | 120 |
CLP5 | 118 (5) | 200 (5) | 265 (5) | 323 (4) | | | |
GFNI | 174 (3) | 251 (3) | 390 (3) | 519 (2) | | | |
GFDI | 152 (3) | 206 (3) | 332 (3) | 459 (2) | | | |
GFDL | 125 (4) | 179 (4) | 271 (4) | 412 (3) | | | |
GFDN | 118 (2) | 221 (2) | 330 (2) | 474 (2) | | | |
LBAR | 108 (5) | 165 (5) | 207 (
5) | 257 (
4) | | | |
AVNI | 135 (3) | 186 (3) | 290 (3) | 385 (2) | | | |
AVNO | 63 (5) | 99 (5) | 180 (5) | 312 (3) | | | |
AEMI | 81 (2) | 100 (2) | 149 (2) | 98 (1) | | | |
BAMD | 122 (5) | 210 (5) | 296 (5) | 387 (4) | | | |
BAMM | 121 (5) | 214 (5) | 300 (5) | 380 (4) | | | |
BAMS | 117 (5) | 208 (5) | 289 (5) | 376 (4) | | | |
NGPI | 131 (4) | 185 (4) | 275 (4) | 343 (3) | | | |
NGPS | 92 (5) | 132 (5) | 209 (5) | 364 (3) | | | |
UKMI | 128 (2) | 148 (2) | 202 (2) | 253 (1) | | | |
UKM | 88 (3) | 92 (2) | 156 (2) | 165 (1) | | | |
A98E | 119 (5) | 207 (5) | 254 (5) | 333 (4) | | | |
A9UK | 111 (3) | 182 (3) | 212 (3) | 279 (2) | | | |
GUNS | 142 (2) | 194 (2) | 302 (2) | 392 (1) | | | |
GUNA | 137 (2) | 193 (2) | 301 (2) | 389 (1) | | | |
OFCL | 108 (5) | 158 (5) | 223 (5) | 305 (4) | | | |
NHC Official (1993-2002 mean) | 45 (2985) | 81 (2726) | 116 (2481) | 150 (2230) | | | |
|
Table 5: Watch and warning
summary for Tropical Storm Grace, 30 August-2 September 2003.
Date/Time | Action | Location |
30 / 1500 | Tropical Storm Warning Issued | High Island, TX to Corpus Christi, TX |
31 / 1500 | Tropical Storm Warning Discontinued | |
Figure 1:
Best track positions for
Tropical Storm Grace, 30 August-2 September 2003. Tropical
depression positions inland are based on analyses from the NOAA
Tropical Prediction Center/ National Hurricane Center and the
Hydrometeorological Prediction Center (HPC).
Figure 2:
Selected wind observations
and best track maximum sustained surface
wind speed curve for Tropical Storm Grace, 30 August- 2 September
2003.Aircraft observations have been
adjusted for elevation using an 80% reduction factors for
observations from 850 mb and 1500 ft.Estimates during the inland weakening stage are based on
analyses from the NOAA Tropical Prediction Center/ National
Hurricane Center and the Hydrometeorological Prediction Center
(HPC).
Figure 3:
Selected pressure
observations and best track minimum central
pressure curve for Tropical Storm Grace, 30 August - 2 September
2003.ObjectiveEstimates during the inland weakening stage are based on
analyses from the NOAA Tropical Prediction Center/ National
Hurricane Center and the Hydrometeorological Prediction Center
(HPC).
Figure 4:
The five official track
forecasts (dashed lines, with 0, 12, 24, 36 ,48, and 72 h positions
indicated) for Tropical Storm Grace, 30 August - 2 September
2003.The best track is given by the thick
solid line with positions given at 6 h intervals. The
poorly-defined low-level center, including its redevelopment
farther north, led to unusually large track forecast
errors.
|