Number range CHAPTERTropical Cyclone Report

Tropical Storm Gil (EP102007)

29 August -2 September 2007

Lixion A. Avila

National Hurricane Center

10 October 2007

Gil was a short-lived tropical cyclone that spent its lifetime over
water.

a\. Synoptic History

A vigorous tropical wave left the west coast of Senegal, Africa, on 16
August. The wave had a large amplitude, abundant convection, and
pressure falls on the order of 6 mb in 24 hours. The wave moved westward
over the tropical Atlantic for several days maintaining its large
envelope and intermittent thunderstorm activity. The wave became less
distinct on the 21^st^ when it interacted with a large upper-level
trough centered over the eastern Caribbean Sea. The wave continued
westward across the Caribbean Sea and Central America, and the northern
portion of the wave spawned a weak low pressure area in the Bay of
Campeche on 26 August. However, most of the convective activity
associated with the southern portion of the wave continued westward over
Mexico.

The wave emerged over the eastern North Pacific on 27 August, and the
shower activity became concentrated just south of Cabo Corrientes,
Mexico. The system continued westward and became better organized as it
developed additional thunderstorms with a few convective bands. It is
estimated that a tropical depression formed at 1200 UTC 29 August about
240 n mi south-southeast of the southern tip of Baja California, and it
became a tropical storm six hours later. The center of Gil was located
on the northeastern edge of the convection due to strong northeasterly
shear, which inhibited further intensification. The cyclone's peak winds
reached only 40 knots and a minimum pressure of 1001 mb at 1200 UTC 30
August. Thereafter, gradual weakening occurred due to both shear and
cooler waters. Gil became a westward-moving remnant low at 1800 UTC 2
September and dissipated later that day.

The "best track" chart of the tropical cyclone'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.

b.  Meteorological Statistics

    Observations in Gil (Figs. 2 and 3) include satellite-based Dvorak
    technique intensity estimates from the Tropical Analysis and
    Forecast Branch (TAFB) and the Satellite Analysis Branch (SAB).
    Microwave data from polar-orbiting satellites were useful in
    tracking Gil, in particular to determine that the center was
    partially removed from the convection. The 40-knot peak intensity
    estimate for Gil was based on a QuikSCAT pass around 1300 UTC 30
    August.

c\. Casualty and Damage Statistics

There are no reports of casualties or damage associated with Gil.

d\. Forecast and Warning Critique

The description of the disturbance from which Gil originated was
included in Tropical Weather Outlook (TWO) products beginning on 26
August. The possibility of tropical cyclone formation was included in
the TWO issued at 1700 UTC 28 August, about 19 h prior to genesis.

Average official track errors (with the number of cases in parentheses)
for Gil were 25 (15), 43 (13), 67 (11), 86 (9) and 104 (5) n mi for the
12, 24, 36, 48 and 72 h forecasts, respectively. These errors are below
the average official track errors for the 5-yr period 2002-2006 of 33,
57, 79, 99, and 140 n mi, respectively. Table 2 displays the forecast
track model statistics and shows a comparison with the official forecast
errors and the 5-year official mean errors.

Average official intensity errors were 3, 5, 7, 7, and 1 kt for the 12,
24, 36, 48 and 72h forecasts, respectively. The long-term average
official intensity errors are 6, 11, 15, 17, 19, and 19 kt for the same
5-yr period. Table 3 includes the forecast intensity model statistics as
well as the average official intensity forecast errors and the 5-year
official mean errors.

No watches or warnings were required for Gil.

Number range CHAPTER

Number range CHAPTERTable 1. Best track for Tropical Storm Gil, 29
August - 2 September 2007.

+-----------+---------+---------+--------+-----------+----------------+
| Date/Time | L       | Lo      | Pr     | Wind      | Stage          |
|           | atitude | ngitude | essure | Speed     |                |
| (UTC)     |         |         |        |           |                |
|           | (°N)    | (°W)    | (mb)   | (kt)      |                |
+-----------+---------+---------+--------+-----------+----------------+
| 29 / 1200 | 19.4    | 109.0   | 1004   | 30        | tropical       |
|           |         |         |        |           | depression     |
+-----------+---------+---------+--------+-----------+----------------+
| 29 / 1800 | 19.5    | 110.0   | 1003   | 35        | tropical storm |
+-----------+---------+---------+--------+-----------+----------------+
| 30 / 0000 | 19.4    | 111.2   | 1003   | 35        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 30 / 0600 | 19.2    | 112.2   | 1003   | 40        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 30 / 1200 | 19.2    | 113.1   | 1001   | 40        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 30 / 1800 | 19.2    | 114.0   | 1002   | 40        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 31 / 0000 | 19.1    | 114.9   | 1002   | 40        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 31 / 0600 | 19.0    | 115.9   | 1003   | 35        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 31 / 1200 | 18.8    | 116.9   | 1004   | 35        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 31 / 1800 | 18.7    | 117.8   | 1005   | 35        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 01 / 0000 | 18.6    | 118.6   | 1005   | 30        | tropical       |
|           |         |         |        |           | depression     |
+-----------+---------+---------+--------+-----------+----------------+
| 01 / 0600 | 18.6    | 119.5   | 1005   | 30        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 01 / 1200 | 18.8    | 120.3   | 1005   | 25        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 01 / 1800 | 19.0    | 121.2   | 1005   | 25        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 02 / 0000 | 19.2    | 122.1   | 1005   | 25        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 02 / 0600 | 19.4    | 122.9   | 1005   | 25        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 02 / 1200 | 19.6    | 123.7   | 1006   | 25        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 02 / 1800 | 20.0    | 123.9   | 1007   | 20        | low            |
+-----------+---------+---------+--------+-----------+----------------+
| 03 / 0000 | 20.3    | 124.2   | 1008   | 20        | \"             |
+-----------+---------+---------+--------+-----------+----------------+
| 03 / 0600 |         |         |        |           | dissipated     |
+-----------+---------+---------+--------+-----------+----------------+
| 30 / 1200 | 19.2    | 113.1   | 1001   | 40        | minimum        |
|           |         |         |        |           | pressure       |
+-----------+---------+---------+--------+-----------+----------------+

Table. 2. Preliminary forecast evaluation (heterogeneous sample) for
Tropical Storm Gil, 29 August -2 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, but does not include the extratropical
stage, if any.

+-----------+-------+-------+-------+-------+-------+-------+-------+
| Number    | For   |       |       |       |       |       |       |
| range     | ecast |       |       |       |       |       |       |
| CHAPTE    | P     |       |       |       |       |       |       |
| RForecast | eriod |       |       |       |       |       |       |
| Technique | (h)   |       |       |       |       |       |       |
+===========+=======+=======+=======+=======+=======+=======+=======+
|           | 12    | 24    | 36    | 48    | 72    | 96    | 120   |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CLP5      | 28    | 50    | **66  | 88 (  | 179 ( | 335 ( |       |
|           | (15)  | (13)  | (     | 9)    | 5)    | 1)    |       |
|           |       |       | 11)** |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFNI      | 28    | 46    | **66  | **79  | **90  |       |       |
|           | (13)  | (11)  | (     | (     | (     |       |       |
|           |       |       | 9)**  | 7)**  | 2)**  |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDI      | 36    | 65    | 103   | 132 ( | 169 ( |       |       |
|           | (15)  | (13)  | (11)  | 9)    | 4)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFSI      | 46    | 80    | 102   | 113 ( | 169 ( |       |       |
|           | (15)  | (13)  | (11)  | 9)    | 5)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| AEMI      | 29    | 44    | **56  | **78  | 139 ( |       |       |
|           | (15)  | (13)  | (     | (     | 5)    |       |       |
|           |       |       | 11)** | 9)**  |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NGPI      | 25    | **31  | **41  | **64  | 148 ( |       |       |
|           | (15)  | (     | (     | (     | 3)    |       |       |
|           |       | 11)** | 9)**  | 7)**  |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| UKMI      | 36    | 61    | 79    | 96 (  | 131 ( |       |       |
|           | (14)  | (12)  | (10)  | 8)    | 4)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMD      | 56    | 115   | 189   | 265 ( | 443 ( | 490 ( |       |
|           | (15)  | (13)  | (11)  | 9)    | 5)    | 1)    |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMM      | 56    | 116   | 191   | 272 ( | 447 ( | 465 ( |       |
|           | (15)  | (13)  | (11)  | 9)    | 5)    | 1)    |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMS      | 48    | 96    | 154   | 214 ( | 343 ( | 380 ( |       |
|           | (15)  | (13)  | (11)  | 9)    | 5)    | 1)    |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CONU      | 27    | **41  | **56  | 71 (  | 105 ( |       |       |
|           | (15)  | (     | (     | 9)    | 4)    |       |       |
|           |       | 13)** | 11)** |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GUNA      | 26    | **41  | **66  | 86 (  | 146 ( |       |       |
|           | (14)  | (     | (     | 7)    | 3)    |       |       |
|           |       | 11)** | 9)**  |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| FSSE      | 33 (  | 66 (  | 94 (  | 109 ( |       |       |       |
|           | 9)    | 9)    | 8)    | 6)    |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | 25    | 43    | 67    | 86 (  | 104 ( |       |       |
|           | (15)  | (13)  | (11)  | 9)    | 5)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 33    | 57    | 79    | 99    | 140   | 188   | 233   |
| Official  | (     | (     | (     | (897) | (655) | (465) | (311) |
|           | 1349) | 1192) | 1039) |       |       |       |       |
| (         |       |       |       |       |       |       |       |
| 2002-2006 |       |       |       |       |       |       |       |
| mean)     |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

Table 3. Preliminary intensity forecast evaluation (heterogeneous
sample) for Tropical Storm Gil, 29 August- 2 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, but does not include
the extratropical stage, if any.

+----------+--------+--------+--------+--------+--------+-------+---+
| Number   | Fo     |        |        |        |        |       |   |
| range    | recast |        |        |        |        |       |   |
| CHAPTER  | Period |        |        |        |        |       |   |
| Forecast | (h)    |        |        |        |        |       |   |
| T        |        |        |        |        |        |       |   |
| echnique |        |        |        |        |        |       |   |
+==========+========+========+========+========+========+=======+===+
|          | 12     | 24     | 36     | 48     | 72     | 96    | 1 |
|          |        |        |        |        |        |       | 2 |
|          |        |        |        |        |        |       | 0 |
+----------+--------+--------+--------+--------+--------+-------+---+
| SHF5     | 3.5    | 5.9    | 11.5   | 13.9 ( | 23.6 ( | 25.0  |   |
|          | (15)   | (13)   | (11)   | 9)     | 5)     | ( 1)  |   |
+----------+--------+--------+--------+--------+--------+-------+---+
| GHMI     | 6.8    | 12.7   | 17.5   | 17.1 ( | 6.0 (  |       |   |
|          | (15)   | (13)   | (11)   | 9)     | 4)     |       |   |
+----------+--------+--------+--------+--------+--------+-------+---+
| SHIP     | 3.4    | 6.3    | 10.9   | 14.4 ( | 13.0 ( |       |   |
|          | (15)   | (13)   | (11)   | 9)     | 5)     |       |   |
+----------+--------+--------+--------+--------+--------+-------+---+
| DSHP     | 3.4    | 6.3    | 10.9   | 14.4 ( | 13.0 ( |       |   |
|          | (15)   | (13)   | (11)   | 9)     | 5)     |       |   |
+----------+--------+--------+--------+--------+--------+-------+---+
| FSSE     | 4.7 (  | 6.2 (  | 10.3 ( | 10.3 ( |        |       |   |
|          | 9)     | 9)     | 8)     | 6)     |        |       |   |
+----------+--------+--------+--------+--------+--------+-------+---+
| ICON     | 4.9    | 7.8    | 10.5   | 11.4 ( | 2.5 (  |       |   |
|          | (15)   | (13)   | (11)   | 9)     | 4)     |       |   |
+----------+--------+--------+--------+--------+--------+-------+---+
| OFCL     | 3.0    | 4.6    | 6.8    | 6.7 (  | 1.0 (  |       |   |
|          | (15)   | (13)   | (11)   | 9)     | 5)     |       |   |
+----------+--------+--------+--------+--------+--------+-------+---+
| NHC      | 6.3    | 11.0   | 14.6   | 16.9   | 18.9   | 18.5  |   |
| Official | (1349) | (1192) | (1039) | (896)  | (655)  | (465) |   |
|          |        |        |        |        |        |       |   |
| (2       |        |        |        |        |        |       |   |
| 002-2006 |        |        |        |        |        |       |   |
| mean)    |        |        |        |        |        |       |   |
+----------+--------+--------+--------+--------+--------+-------+---+

![](media/image1.wmf){width="6.493055555555555in" height="5.03125in"}

Number range CHAPTERFigure 1. Best track positions for Tropical Storm
Gil, 29 August -2 September 2007.

![](media/image2.wmf){width="6.497916666666667in"
height="4.438194444444444in"}

Number range CHAPTERFigure 2. Selected wind observations and best track
maximum sustained surface wind speed curve for Tropical Storm Gil, 29
August -2 September 2007.

![](media/image3.wmf){width="6.497916666666667in"
height="4.438194444444444in"}

Number range CHAPTERFigure 3. Selected pressure observations and best
track minimum central pressure curve for Tropical Storm Gil, 29 August
-2 September 2007.