Number range CHAPTERTropical Cyclone Report

Tropical Storm Gabrielle

(AL072007)

8-11 September 2007

Daniel P. Brown

National Hurricane Center

29 October 2007

Gabrielle was a tropical storm that made landfall along the Cape Lookout
National Seashore in eastern North Carolina, and then exited the coast
less than 12 hours later near Kill Devil Hills.

a.  Synoptic History

    The genesis of Gabrielle can be traced back to a low pressure area
    that formed along the coast of Georgia on 3 September. This low
    developed along a frontal boundary that initially moved off the
    southeastern United States coast on 1 September. After forming, the
    weak low moved eastward and remained non-tropical during the next
    several days. The low weakened and became ill-defined on 5-6
    September. The next day, an upper-level trough over the western
    Atlantic began to cut off several hundred miles southwest of
    Bermuda. This mid-to upper-level cut-off low moved slowly
    southwestward and aided in the regeneration of the surface low over
    the western Atlantic. A Hurricane Hunter reconnaissance mission on
    the afternoon of 7 September was unable to find a well-defined
    center of circulation, but it did encounter flight-level winds
    consistent with tropical storm force winds at the surface. Satellite
    imagery suggests that the circulation became better defined late on
    7 September, and based on the improved satellite appearance and the
    peak-flight level winds from the earlier aircraft, it is estimated
    that a subtropical storm formed at 0000 UTC 8 September about 360 n
    mi southeast of Cape Hatteras, North Carolina. The "best track"
    chart of Gabrielle's path is given in Fig. 1, with the wind and
    pressure histories shown in Figs. 2 and 3, respectively. The best
    track positions and intensities are listed in Table 1.

    The satellite appearance of the cyclone remained that of a
    subtropical storm during the next 12 hours as the primary band of
    thunderstorm activity remained well to the north of the center. This
    band gradually weakened and new convection developed just northwest
    of the center, which led to the transition of Gabrielle to a
    tropical storm by 1800 UTC 8 September. Gabrielle gradually
    strengthened while moving northwestward toward eastern North
    Carolina early on 9 September. Before reaching the coast of North
    Carolina, reconnaissance aircraft data revealed that the center of
    Gabrielle reformed closer to the thunderstorm activity, which
    resulted in some additional strengthening. Gabrielle reached a peak
    intensity of 50 kt at 1200 UTC 9 September, while centered just
    south-southeast of Cape Lookout, North Carolina. A few hours later,
    the center of Gabrielle made landfall along the Cape Lookout
    National Seashore; however, strong northerly upper-level winds
    initially kept the convection and strongest surface winds offshore.
    Shortly thereafter, Gabrielle weakened due to the northerly wind
    shear and its interaction with land. While over extreme eastern
    North Carolina, Gabrielle turned northeastward and exited the coast
    near Kill Devil Hills just after 0000 UTC 10 September. After moving
    back over the Atlantic waters, thunderstorm activity continued to
    decrease and became even more removed from the center, and Gabrielle
    weakened to a tropical depression by 0600 UTC 10 September. The
    depression moved east-northeastward, passing well southeast of the
    coast of the northeastern United States. The circulation of
    Gabrielle weakened and dissipated ahead of a frontal boundary by
    1200 UTC 11 September about 300 n mi south-southwest of Nova Scotia.

b.  Meteorological Statistics

    Observations in Gabrielle (Figs. 2 and 3) include satellite-based
    Hebert-Poteat and Dvorak technique intensity estimates from the
    Tropical Analysis and Forecast Branch (TAFB) and the Satellite
    Analysis Branch (SAB), as well as flight-level and dropwindsonde
    observations from flights of the 53^rd^ Weather Reconnaissance
    Squadron of the U. S. Air Force Reserve Command. Microwave satellite
    imagery from NOAA polar-orbiting satellites, the NASA Tropical
    Rainfall Measuring Mission (TRMM), the NASA Aqua, the NASA QuikSCAT,
    the Department of Defense WindSat, and Defense Meteorological
    Satellite Program (DMSP) satellites were also useful in tracking
    Gabrielle. Conventional land-based surface observations, buoys,
    C-MAN stations, and National Weather Service Doppler radar data were
    helpful in tracking the path of Gabrielle over eastern North
    Carolina.

    The strengthening of Gabrielle just southeast of the North Carolina
    coast was well documented by reconnaissance aircraft. The aircraft
    data indicate that the center of Gabrielle reformed just after 0900
    UTC 9 September near a mid-level center seen in satellite imagery,
    which was associated with a band of very strong thunderstorms.
    Shortly after this time, a 925 mb flight-level wind of 61 kt was
    reported. A subsequent reconnaissance flight avoided this area of
    strong thunderstorms due to safety concerns. However, just prior to
    Gabrielle's landfall the aircraft flew near the edge of the strong
    convection and measured a peak flight-level wind of 66 kt at 850 mb.
    A dropsonde released near the peak flight-level winds measured a
    surface wind of 49 kt, however applying a standard wind reduction
    using the mean of the lowest 150-m winds from this sonde results in
    a slightly lower wind estimate. The 50 kt peak intensity is based on
    a consensus of the sonde data and the flight-level winds reduced to
    the surface using a standard reduction.

    Even though Gabrielle's intensity is estimated at 50 kt at landfall,
    these strong winds never reached the coast, as northerly shear kept
    the strongest thunderstorm activity offshore for several hours. By
    the time this activity reached the coast, the maximum winds had
    decreased a little. Selected surface observations from land stations
    and data buoys are given in Table 2. The highest sustained wind
    measured in eastern North Carolina was 38 kt at Frisco Pier. A wind
    gust to 46 kt was reported at Cape Hatteras and a wind gust to 53 kt
    was observed at Ocracoke. Heavy rainfall associated with Gabrielle
    was confined to a rather small area of eastern North Carolina. Four
    to eight inches of rain fell across southern Craven and eastern
    Carteret Counties with a maximum amount of 9.03 inches reported near
    Harlowe in Carteret County. An estimated storm surge of 1 to 2 ft
    occurred along the Atlantic facing beaches of Carteret, Hyde and
    Dare counties, and a sound-side storm surge of 2 to 3 ft was
    reported in portions of Dare County.

    Two ship reports of tropical storm force winds were received in
    association with Gabrielle. A history of quality controlled data
    from these ships suggests that these winds are likely too high.

c.  Casualty and Damage Statistics

    Overall, impacts from Gabrielle were minimal in eastern North
    Carolina. Reports indicate that storm surge and higher than normal
    tidal levels contributed to an over-wash of Highway 12 in Dare
    County, north of Cape Hatteras near Salvo and Rodanthe. Minor beach
    erosion was also reported along the south facing beaches of
    Carteret, Hyde, and southern Dare Counties. A few streets in
    Morehead City and Beaufort were closed due to heavy rainfall and
    several homes and businesses suffered minor flood damage. There were
    no reports of casualties associated with Gabrielle.

d.  Forecast and Warning Critique

    The genesis of Gabrielle was well anticipated in Tropical Weather
    Outlooks issued by the National Hurricane Center. The incipient
    disturbance from which Gabrielle formed was first discussed in the
    Outlook at 1530 UTC 2 September. This and subsequent Outlooks issued
    during the next couple of days discussed the possibility of slow
    development of this system. The first explicit mention of possible
    tropical or subtropical cyclone formation was made at 0930 UTC 4
    September, several days before Gabrielle formed. Experimental
    probability of genesis forecasts made during the 48-h period prior
    to formation of this system ranged from 20 to 90%.

    A verification of official and guidance model track forecasts is
    given in Table 3. Average official track errors (with number of
    cases in parenthesis) for Gabrielle were 20 (12), 31 (10), 46 (8),
    62 (6), 154 (2) n mi for the 12, 24, 36, 48, and 72 h forecasts,
    respectively. There were no 96 or 120 h forecasts that verified. The
    official track errors through 48 hours are nearly half of the
    average 5-year (2002-2006) official track errors (Table 3), while
    the 72 h error is slightly below the 5-year mean. The NHC forecasts
    in general accurately predicted Gabrielle's path across eastern
    North Carolina, but showed a little northwestward bias after its
    re-curvature. The official forecasts were better than all the track
    guidance through 24 h and only the medium Beta and Advection Model
    (BAM) and the interpolated GFS model were better than the NHC
    predictions at 36, 48 and 72 h. The NHC track forecasts were better
    than the CONU and GUNA model consensus forecasts at all time
    periods.

    Average official intensity errors (Table 4) were 5, 6, 12, 16, and
    15 kt for the 12, 24, 36, 48, and 72 h forecasts respectively. The
    intensity forecast errors are a little smaller than the 5-year mean,
    except at 48 h. The official intensity forecasts predicted that
    Gabrielle would remain a tropical storm after exiting the coast of
    North Carolina, and this resulted in a high bias in some of the
    forecasts.

    Table 5 is a summary of coastal watches and warnings issued in
    association with Gabrielle. Tropical storm warnings were issued in a
    timely manner (24 h or more in advance of landfall) for eastern
    North Carolina.

    e\. Acknowledgements

    Most of the surface observations in this report were provided by
    National Weather Service (NWS) Offices in Morehead City, North
    Carolina and Wakefield, Virginia. Additional observations from buoys
    and C-MANs were provided by the National Data Buoy Center (NDBC).
    WeatherFlow provided additional surface observations that were
    useful both operationally and in the post-storm analysis.

Number range CHAPTERTable 1. Best track for Tropical Storm Gabrielle,
8-11 September 2007.

+---------+---------+---------+-----------+---------+----------------+
| Da      | L       | Lo      | Pressure  | Wind    | Stage          |
| te/Time | atitude | ngitude |           | Speed   |                |
|         |         |         | (mb)      |         |                |
| (UTC)   | (°N)    | (°W)    |           | (kt)    |                |
+---------+---------+---------+-----------+---------+----------------+
| 08 /    | 30.1    | 71.8    | 1011      | 40      | subtropical    |
| 0000    |         |         |           |         | storm          |
+---------+---------+---------+-----------+---------+----------------+
| 08 /    | 30.5    | 72.8    | 1010      | 40      | \"             |
| 0600    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 08 /    | 31.1    | 73.8    | 1010      | 35      | \"             |
| 1200    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 08 /    | 31.8    | 74.6    | 1009      | 35      | tropical storm |
| 1800    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 09 /    | 32.6    | 75.4    | 1007      | 40      | \"             |
| 0000    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 09 /    | 33.5    | 76.0    | 1004      | 45      | \"             |
| 0600    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 09 /    | 34.3    | 76.4    | 1004      | 50      | \"             |
| 1200    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 09 /    | 35.2    | 76.3    | 1006      | 45      | \"             |
| 1800    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 10 /    | 36.0    | 75.8    | 1007      | 40      | \"             |
| 0000    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 10 /    | 36.7    | 75.0    | 1008      | 30      | tropical       |
| 0600    |         |         |           |         | depression     |
+---------+---------+---------+-----------+---------+----------------+
| 10 /    | 37.1    | 73.8    | 1009      | 30      | \"             |
| 1200    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 10 /    | 37.5    | 72.0    | 1010      | 30      | \"             |
| 1800    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 11 /    | 37.9    | 70.0    | 1010      | 30      | \"             |
| 0000    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 11 /    | 38.4    | 68.0    | 1010      | 30      | \"             |
| 0600    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 11 /    |         |         |           |         | dissipated     |
| 1200    |         |         |           |         |                |
+---------+---------+---------+-----------+---------+----------------+
| 09 /    | 34.3    | 76.4    | 1004      | 50      | Maximum wind   |
| 1200    |         |         |           |         | and minimum    |
|         |         |         |           |         | pressure       |
+---------+---------+---------+-----------+---------+----------------+
| 09/1530 | 34.8    | 76.4    | 1005      | 50      | Landfall along |
|         |         |         |           |         | Cape Lookout   |
|         |         |         |           |         | National       |
|         |         |         |           |         | Seashore, NC   |
+---------+---------+---------+-----------+---------+----------------+

Number range CHAPTERTable 2. Selected surface observations for
Gabrielle, 8-11 September 2007.

+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Location        | M   |     | M   |       |     | St  | St  | To  |
|                 | ini |     | axi |       |     | orm | orm | tal |
|                 | mum |     | mum |       |     | su  |     |     |
|                 | Sea |     | S   |       |     | rge | t   | r   |
|                 | Le  |     | urf |       |     |     | ide | ain |
|                 | vel |     | ace |       |     | (   |     |     |
|                 | Pr  |     |     |       |     | ft) | (   | (   |
|                 | ess |     | W   |       |     | ^c^ | ft) | in) |
|                 | ure |     | ind |       |     |     | ^d^ |     |
|                 |     |     | Sp  |       |     |     |     |     |
|                 |     |     | eed |       |     |     |     |     |
+=================+=====+=====+=====+=======+=====+=====+=====+=====+
|                 | Da  | Pre | Da  | Sust  | G   |     |     |     |
|                 | te/ | ss. | te/ | ained | ust |     |     |     |
|                 |     |     |     |       |     |     |     |     |
|                 | t   | (   | t   | (k    | (   |     |     |     |
|                 | ime | mb) | ime | t)^b^ | kt) |     |     |     |
|                 |     |     |     |       |     |     |     |     |
|                 | (U  |     | (U  |       |     |     |     |     |
|                 | TC) |     | TC) |       |     |     |     |     |
|                 |     |     | ^a^ |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **North         |     |     |     |       |     |     |     |     |
| Carolina**      |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Official**    |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Beaufort (KMRH) | 0   | 100 | 0   | 29    | 38  |     |     | 7   |
|                 | 9/1 | 8.5 | 9/1 |       |     |     |     | .43 |
|                 | 315 |     | 907 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Beaufort 6 N    |     |     |     |       |     |     |     | 8   |
|                 |     |     |     |       |     |     |     | .30 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Cape Hatteras   | 0   | 101 | 0   | 34    | 46  |     |     | 0   |
| (KHSE)          | 9/2 | 0.5 | 9/2 |       |     |     |     | .23 |
|                 | 015 |     | 341 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Cedar Island    | 0   | 100 |     |       |     |     |     |     |
| (CITN7)         | 9/1 | 8.0 |     |       |     |     |     |     |
|                 | 550 |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Cherry Point    | 0   | 101 |     |       |     |     |     | 4   |
| (KNKT)          | 9/1 | 0.5 |     |       |     |     |     | .52 |
|                 | 954 |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| New Bern (KEWN) | 0   | 101 |     |       |     |     |     | 1   |
|                 | 9/2 | 0.5 |     |       |     |     |     | .89 |
|                 | 001 |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| New Bern RAWS   |     |     |     |       |     |     |     | 1   |
|                 |     |     |     |       |     |     |     | .12 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Newport NWS     |     |     |     |       |     |     |     | 5   |
|                 |     |     |     |       |     |     |     | .36 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Ocracoke COOP   |     |     |     |       | 49  |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Stumpy Point    | 0   | 100 | 0   | 30    | 36  |     |     |     |
| (SP0N7)         | 9/2 | 9.0 | 9/1 |       |     |     |     |     |
|                 | 220 |     | 820 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Swanquarter     | 0   | 100 |     |       |     |     |     |     |
| (SWQN7)         | 9/1 | 7.0 |     |       |     |     |     |     |
|                 | 820 |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
|                 |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Unofficial**  |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Avon Ocean      | 0   | 100 | 0   | 34    | 40  |     |     |     |
| (WeatherFlow)   | 9/1 | 9.0 | 9/1 |       |     |     |     |     |
|                 | 931 |     | 800 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Davis Mesonet   |     |     |     |       |     |     |     | 4   |
|                 |     |     |     |       |     |     |     | .88 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Frisco Pier     | 0   | 100 | 0   | 38    | 45  |     |     |     |
| (WeatherFlow)   | 9/1 | 9.5 | 9/2 |       |     |     |     |     |
|                 | 928 |     | 330 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Frisco Woods    | 0   | 100 | 0   | 35    | 43  |     |     |     |
| (WeatherFlow)   | 9/1 | 9.5 | 9/2 |       |     |     |     |     |
|                 | 946 |     | 237 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Harlowe (7.2    |     |     |     |       |     |     |     | 9   |
| ENE Newport)    |     |     |     |       |     |     |     | .03 |
| (COCORAHS)      |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Indian Beach    |     |     | 0   |       | 37  |     |     |     |
|                 |     |     | 9/2 |       |     |     |     |     |
|                 |     |     | 000 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Indian Beach    |     |     |     |       |     |     |     | 2   |
| Mesonet         |     |     |     |       |     |     |     | .19 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Morehead City   |     |     |     |       |     |     |     | 7   |
|                 |     |     |     |       |     |     |     | .70 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Morehead City   |     |     |     |       |     |     |     | 7   |
|                 |     |     |     |       |     |     |     | .53 |
| Waste Water     |     |     |     |       |     |     |     |     |
| Plant           |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Morehead City   |     |     |     |       |     |     |     | 7   |
| (2.9 WNW)       |     |     |     |       |     |     |     | .07 |
|                 |     |     |     |       |     |     |     |     |
| (COCORAHS)      |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Morehead City   |     |     |     |       |     |     |     | 6   |
| Mesonet         |     |     |     |       |     |     |     | .93 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Morehead City   |     |     |     |       | 41  |     |     |     |
| State Port      |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Newport (0.2    |     |     |     |       |     |     |     | 5   |
| SW) (COCORAHS)  |     |     |     |       |     |     |     | .50 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Ocracoke        |     |     |     |       | 53  |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Ocracoke        | 0   | 100 | 0   | 37    | 43  |     |     |     |
| (WeatherFlow)   | 9/1 | 8.1 | 9/1 |       |     |     |     |     |
|                 | 803 |     | 711 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Ocracoke Island | 0   | 100 | 0   |       | 37  |     |     |     |
|                 | 9/1 | 7.3 | 9/2 |       |     |     |     |     |
| (Weather        | 750 |     | 000 |       |     |     |     |     |
| Underground)    |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Smyrna          |     |     |     |       |     |     |     | 6   |
| (COCORAHS)      |     |     |     |       |     |     |     | .85 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
|                 |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Buoy/CMAN**   |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 41035- Inner    | 0   | 101 | 0   | 27    | 34  |     |     |     |
| Onslow Bay      | 9/0 | 1.0 | 9/2 | ^e^   |     |     |     |     |
|                 | 920 |     | 200 |       |     |     |     |     |
| (34.5ºN 77.3ºW) |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Cape Lookout    | 0   | 100 | 0   | 24    | 35  |     |     |     |
| (CLKN7)         | 9/1 | 7.3 | 9/2 | ^e^   |     |     |     |     |
|                 | 400 |     | 030 |       |     |     |     |     |
| (34.6ºN 76.5ºW) |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 41025- Diamond  | 0   | 101 | 1   | 36    | 45  |     |     |     |
| Shoals          | 9/1 | 0.6 | 0/0 | ^e^   |     |     |     |     |
|                 | 950 |     | 120 |       |     |     |     |     |
| (35.0ºN 75.4ºW) |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 44014-E of      | 1   | 100 | 1   | 28    | 35  |     |     |     |
| Virginia Beach  | 0/0 | 9.3 | 0/0 | ^e^   |     |     |     |     |
|                 | 550 |     | 430 |       |     |     |     |     |
| (36.6ºN 74.8ºW) |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+

^a^ Date/time is for sustained wind when both sustained and gust are
listed.

^b^ Except as noted, sustained wind averaging periods for C-MAN and
land-based ASOS reports are 2 min; buoy averaging periods are 8 min.

^c^ Storm surge is water height above normal astronomical tide level.

^d^ Storm tide is water height above National Geodetic Vertical Datum
(1929 mean sea level).

^e^ 10-minute average.

Number range CHAPTERTable 3. Preliminary track forecast evaluation
(heterogeneous sample) for Tropical Storm Gabrielle, 8-11 September
2007. 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.

+-----------+-------+-------+-------+-------+-------+-------+-------+
| Number    | For   |       |       |       |       |       |       |
| range     | ecast |       |       |       |       |       |       |
| CHAPTE    | P     |       |       |       |       |       |       |
| RForecast | eriod |       |       |       |       |       |       |
| Technique | (h)   |       |       |       |       |       |       |
+===========+=======+=======+=======+=======+=======+=======+=======+
|           | 12    | 24    | 36    | 48    | 72    | 96    | 120   |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CLP5      | 35    | 87    | 124 ( | 142 ( | 170 ( |       |       |
|           | (12)  | (10)  | 8)    | 6)    | 2)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFNI      | 29    | 55 (  | 109 ( | 154 ( |       |       |       |
|           | (10)  | 8)    | 6)    | 4)    |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDI      | 33    | 58    | 109 ( | 171 ( | 335 ( |       |       |
|           | (12)  | (10)  | 8)    | 6)    | 2)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| HWFI      | 30    | 63    | 97    | 124   | 182   |       |       |
|           | (12)  | (10)  | (8)   | (6)   | (2)   |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFSI      | 26    | 31    | **36  | **58  | **121 |       |       |
|           | (12)  | (10)  | (     | (     | (     |       |       |
|           |       |       | 8)**  | 6)**  | 1)**  |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| AEMI      | 25    | 40    | 53 (  | **60  | **26  |       |       |
|           | (12)  | (10)  | 8)    | (     | (     |       |       |
|           |       |       |       | 5)**  | 1)**  |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NGPI      | 25    | 34    | 48 (  | 69 (  | **132 |       |       |
|           | (12)  | (10)  | 8)    | 6)    | (     |       |       |
|           |       |       |       |       | 2)**  |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| UKMI      | 65    | 218 ( | 457 ( | 120 ( | **122 |       |       |
|           | (11)  | 9)    | 6)    | 2)    | (     |       |       |
|           |       |       |       |       | 1)**  |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMD      | 41    | 66    | 103 ( | 149 ( | 228 ( |       |       |
|           | (12)  | (10)  | 8)    | 6)    | 2)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMM      | 24    | 40    | **43  | **53  | **34  |       |       |
|           | (12)  | (10)  | (     | (     | (     |       |       |
|           |       |       | 8)**  | 6)**  | 2)**  |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMS      | 37    | 62    | 73 (  | 92 (  | 158 ( |       |       |
|           | (12)  | (10)  | 8)    | 6)    | 2)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CONU      | 25    | 51    | 93 (  | 82 (  | 174 ( |       |       |
|           | (12)  | (10)  | 8)    | 6)    | 2)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GUNA      | 29    | 64 (  | 130 ( | 59 (  |       |       |       |
|           | (11)  | 9)    | 6)    | 2)    |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| FSSE      | 21 (  | 36 (  | 60 (  | 97 (  | **140 |       |       |
|           | 9)    | 9)    | 7)    | 4)    | (     |       |       |
|           |       |       |       |       | 1)**  |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | 20    | 31    | 46 (  | 62 (  | 154 ( |       |       |
|           | (12)  | (10)  | 8)    | 6)    | 2)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 35    | 61    | 86    | 112   | 162   | 221   | 290   |
| Official  | (     | (     | (     | (     | (     | (885) | (723) |
|           | 1852) | 1686) | 1519) | 1362) | 1100) |       |       |
| (         |       |       |       |       |       |       |       |
| 2002-2006 |       |       |       |       |       |       |       |
| mean)     |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

Table 4. Preliminary intensity forecast evaluation (heterogeneous
sample) for Tropical Storm Gabrielle, 8-11 September 2007. Forecast
errors (kt) 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.

+-----------+-------+--------+-------+-------+-------+-------+-------+
| Number    | For   |        |       |       |       |       |       |
| range     | ecast |        |       |       |       |       |       |
| CHAPTE    | P     |        |       |       |       |       |       |
| RForecast | eriod |        |       |       |       |       |       |
| Technique | (h)   |        |       |       |       |       |       |
+===========+=======+========+=======+=======+=======+=======+=======+
|           | 12    | 24     | 36    | 48    | 72    | 96    | 120   |
+-----------+-------+--------+-------+-------+-------+-------+-------+
| SHF5      | 8.8   | 11.3   | 21.5  | 28.8  | 42.5  |       |       |
|           | (12)  | (10)   | ( 8)  | ( 6)  | ( 2)  |       |       |
+-----------+-------+--------+-------+-------+-------+-------+-------+
| GHMI      | 7.6   | 7.8    | **9.1 | *     | 30.5  |       |       |
|           | (12)  | (10)   | (     | *14.5 | ( 2)  |       |       |
|           |       |        | 8)**  | (     |       |       |       |
|           |       |        |       | 6)**  |       |       |       |
+-----------+-------+--------+-------+-------+-------+-------+-------+
| HWFI      | 6.0   | **4.5  | **6.0 | **7.5 | 16.0  |       |       |
|           | (12)  | (10)** | (8)** | (6)** | (2)   |       |       |
+-----------+-------+--------+-------+-------+-------+-------+-------+
| SHIP      | 7.8   | 8.8    | 12.6  | 18.8  | 35.0  |       |       |
|           | (12)  | (10)   | ( 8)  | ( 6)  | ( 2)  |       |       |
+-----------+-------+--------+-------+-------+-------+-------+-------+
| DSHP      | 8.0   | 9.6    | 13.0  | *     | 15.5  |       |       |
|           | (12)  | (10)   | ( 8)  | *13.8 | ( 2)  |       |       |
|           |       |        |       | (     |       |       |       |
|           |       |        |       | 6)**  |       |       |       |
+-----------+-------+--------+-------+-------+-------+-------+-------+
| FSSE      | 8.3 ( | 9.6 (  | 14.6  | 22.3  | 35.0  |       |       |
|           | 9)    | 9)     | ( 7)  | ( 4)  | ( 1)  |       |       |
+-----------+-------+--------+-------+-------+-------+-------+-------+
| ICON      | 7.1   | 6.1    | **8.6 | *     | 17.5  |       |       |
|           | (12)  | (10)   | (     | *11.7 | ( 2)  |       |       |
|           |       |        | 8)**  | (     |       |       |       |
|           |       |        |       | 6)**  |       |       |       |
+-----------+-------+--------+-------+-------+-------+-------+-------+
| OFCL      | 5.0   | 6.0    | 11.9  | 15.8  | 15.0  |       |       |
|           | (12)  | (10)   | ( 8)  | ( 6)  | ( 2)  |       |       |
+-----------+-------+--------+-------+-------+-------+-------+-------+
| NHC       | 6.4   | 9.8    | 12.0  | 14.1  | 18.3  | 19.8  | 21.8  |
| Official  |       |        | (     | (     | (     |       |       |
|           | \(1   | \(     | 1519) | 1362) | 1100) | \(    | \(    |
| (         | 852\) | 1686\) |       |       |       | 885\) | 723\) |
| 2002-2006 |       |        |       |       |       |       |       |
| mean)     |       |        |       |       |       |       |       |
+-----------+-------+--------+-------+-------+-------+-------+-------+

Number range CHAPTERTable 5. Watch and warning summary for Tropical
Storm Gabrielle, 8-11 September 2007.

+---------+------------------------------+----------------------------+
| Da      | Action                       | Location                   |
| te/Time |                              |                            |
| (UTC)   |                              |                            |
+---------+------------------------------+----------------------------+
| 8/ 0300 | Tropical Storm Watch issued  | Edisto Beach, SC to Oregon |
|         |                              | Inlet, NC including        |
|         |                              | Pamlico Sound              |
+---------+------------------------------+----------------------------+
| 8/ 1500 | Tropical Storm Warning       | Surf City, NC to the NC/VA |
|         | issued                       | border including the       |
|         |                              | Pamlico and Albermarle     |
|         |                              | Sounds                     |
+---------+------------------------------+----------------------------+
| 8/ 1500 | Tropical Storm Watch issued  | NC/VA border to Cape       |
|         |                              | Charles Light on the       |
|         |                              | Atlantic Coast and to New  |
|         |                              | Point Comfort along the    |
|         |                              | Chesapeake Bay             |
+---------+------------------------------+----------------------------+
| 8/ 1500 | Tropical Storm Watch         | Edisto Beach to Cape Fear  |
|         | discontinued                 |                            |
+---------+------------------------------+----------------------------+
| 8/ 2100 | Tropical Storm Watch         | South of Surf City to Cape |
|         | discontinued                 | Fear                       |
+---------+------------------------------+----------------------------+
| 9/ 0300 | Tropical Storm Warning       | NC/VA border to Cape       |
|         | issued                       |                            |
|         |                              | Charles Light              |
+---------+------------------------------+----------------------------+
| 9/ 0300 | Tropical Storm Watch         | Lower Chesapeake Bay south |
|         | modified to                  | of New Point Comfort       |
+---------+------------------------------+----------------------------+
| 10/     | Tropical Storm Warning       | Surf City to Cape Lookout  |
| 0000    | discontinued                 |                            |
+---------+------------------------------+----------------------------+
| 10/     | Tropical Storm Warning       | All                        |
| 0300    | discontinued                 |                            |
+---------+------------------------------+----------------------------+
| 10/     | Tropical Storm Watch         | All                        |
| 0900    | discontinued                 |                            |
+---------+------------------------------+----------------------------+

![](media/image1.wmf){width="8.002777777777778in"
height="6.158333333333333in"}

Number range CHAPTERFigure 1. Best track positions for Tropical Storm
Gabrielle, 8-11 September 2007.

![](media/image2.wmf){width="7.877777777777778in"
height="5.386111111111111in"}

Number range CHAPTERFigure 2. Selected wind observations and best track
maximum sustained surface wind speed curve for Tropical Storm Gabrielle,
8-11 September 2007. Aircraft observations have been adjusted for
elevation using 90%, 80%, and 80% reduction factors for observations
from 700 mb, 850 mb, and 1500 ft, respectively. Dropwindsonde
observations include actual 10 m winds (sfc), as well as surface
estimates derived from the mean wind over the lowest 150 m of the wind
sounding (LLM), and from the sounding boundary layer mean (MBL). Thin
solid vertical line denotes landfall.

![](media/image3.wmf){width="7.863194444444445in"
height="5.395833333333333in"}

Number range CHAPTERFigure 3. Selected pressure observations and best
track minimum central pressure curve for Tropical Storm Gabrielle, 8-11
September 2007. Thin solid vertical line denotes landfall.