Tropical Cyclone Report

Tropical Storm Ingrid

(AL082007)

12 -- 17 September 2007

Michelle Mainelli

National Hurricane Center

17 October 2007

Ingrid was a tropical storm that formed over the central tropical
Atlantic Ocean and dissipated as it approached the Leeward Islands.

a.  Synoptic History

    Ingrid developed from a large tropical wave that exited the coast of
    Africa on 6 September. At that time, strong easterly shear inhibited
    development over the eastern Atlantic and it was not until 9
    September that a broad area of low pressure developed along the wave
    axis, about midway between Africa and the Lesser Antilles. The
    easterly shear gradually diminished over the next several days,
    which allowed the system to maintain convection near the low center
    on 11 September, when Dvorak classifications were initiated. By the
    morning of 12 September, the system acquired sufficient organization
    to be designated a tropical depression, while centered about 980 n
    mi east of the Lesser Antilles.

    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. The depression moved on a general west-northwestward track
    within a weak steering flow south of a mid-tropospheric ridge.
    Despite moderate westerly shear, the cyclone became a tropical storm
    around 0600 UTC 13 September, while centered about 730 n mi east of
    the Lesser Antilles, and reached its maximum intensity of 40 kts 12
    h later. Persistent westerly shear, due to a stronger than normal
    upper-trophospheric mid-oceanic trough located west-northwest of the
    cyclone, prevented further intensification. During the next 24
    hours, the shear increased, which resulted in Ingrid weakening to a
    tropical depression by 1800 UTC 15 September. Ingrid remained a
    tropical depression for a day or so before degenerating into a
    remnant low around 0600 UTC 17 September, while centered about 140 n
    mi east-northeast of Antigua. The remnants of Ingrid moved slowly
    northwestward and west-northwestward within the lower-tropospheric
    steering flow, and the low dissipated on 18 September.

b.  Meteorological Statistics

    Observations in Ingrid (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), as
    well as flight-level and Stepped Frequency Microwave Radiometer
    (SFMR) surface observations from several flights of the NOAA P-3
    research aircraft. 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 Ingrid.

    The estimated peak intensity of Ingrid on 14 September represents a
    blend of the surface-adjusted flight-level winds and SFMR data from
    the NOAA P-3 aircraft. During the morning flight on 14 September,
    the SFMR reported a maximum 51 knot wind over the southwestern
    quadrant of the storm; however, this observation did not appear
    representative of the strength of the poorly-defined circulation.
    The minimum pressure of 1002 mb is based on a dropsonde pressure of
    1004 mb that was accompanied by a 26-kt surface wind, which
    indicates that the dropsonde probably did not sample the center of
    the cyclone and its lowest pressure.

    No ship or land station reported sustained winds of at least
    tropical storm force in association with Ingrid.

c.  Casualty and Damage Statistics

    There were no reports of damage or casualties associated with
    Ingrid.

d.  Forecast and Warning Critique

    The genesis of Ingrid was well anticipated. The tropical wave that
    eventually spawned Ingrid was first introduced into the Tropical
    Weather Outlook (TWO) at 0230 UTC 7 September, about five days prior
    to genesis. At that time, the wave was located a few hundred miles
    south of the Cape Verde Islands. For the next couple of days, there
    was continual mention in the TWO that slow development of the system
    was possible. By late on 9 September, the potential for tropical
    depression formation was explicitly mentioned in the outlook. It was
    not until early on 12 September that the system acquired enough
    organization to be designated as a tropical depression. This
    resulted in a 54-hour lead time between the first mention of
    potential tropical depression formation in the TWO and when tropical
    cyclogenesis actually occurred.

    A verification of NHC official and guidance model track forecasts is
    given in Table 2. Average official track errors for Ingrid were 28,
    52, 89, 115, 145, and 154 n mi for the 12, 24, 36, 48, 72, and 96 h
    forecasts, respectively. These errors are lower than or close to the
    average long-term official track errors for all forecast periods
    (Table 2). Both the GFSI and UKMI models performed relatively well
    in comparison to the other dynamical model guidance. Notably, the
    UKMI had lower track errors than the official forecasts at all
    forecast lead times except for 24 h. Both the GFSI and UKMI kept a
    more westerly track compared to the other dynamical models during
    the first couple of days. The GFSI and UKMI maintained Ingrid as a
    weak system and anticipated the ridge to the north of the cyclone to
    remain intact. On the other hand, the NGPI had the largest errors as
    it forecasted a stronger Ingrid to take a more northwestward track
    in response to a weakness in the subtropical ridge. Despite somewhat
    of a dichotomy in the model guidance, the official track forecasts
    correctly maintained Ingrid on a more westward track within the low-
    to mid-level steering flow.

    Average NHC official intensity errors were 2, 4, 4, 8, 18, and 28 kt
    for the 12, 24, 36, 48, 72, and 96 h forecasts, respectively (Table
    3). For comparison, the average long-term official intensity errors
    are 6, 10, 12, 14, 18, and 20 kt, respectively. The official
    intensity forecast errors were slightly below the average long-term
    errors through 72 hours; however, they were larger than the average
    error at 96 h. Even though only three official forecasts verified at
    96 h, the larger than average errors at that forecast time can be
    attributed to the global models predicting that the shear would
    lessen, which would allow for gradual strengthening of the cyclone.
    The GHMI provided the most accurate intensity guidance and did
    particularly well in the later forecast periods. It is notable that
    the GFDL Hurricane Model correctly predicted the weakening, in this
    case, in the sheared environment. In earlier years that model was
    notorious for over-intensifying tropical cyclones in environments of
    strong vertical shear. This change could be attributable to recent
    improvements in the GFDL model physics.

Number range CHAPTERTable 1. Best track for Tropical Storm Ingrid, 12-17
September 2007.

+-----------+---+--------+--------+----------+----------+---------------+
| Date/Time | L |        | Lon    | Pressure | Wind     | Stage         |
|           | a |        | gitude |          | Speed    |               |
| (UTC)     | t |        |        | (mb)     |          |               |
|           | i |        | (°W)   |          | (kt)     |               |
|           | t |        |        |          |          |               |
|           | u |        |        |          |          |               |
|           | d |        |        |          |          |               |
|           | e |        |        |          |          |               |
|           |   |        |        |          |          |               |
|           | ( |        |        |          |          |               |
|           | ° |        |        |          |          |               |
|           | N |        |        |          |          |               |
|           | ) |        |        |          |          |               |
+-----------+---+--------+--------+----------+----------+---------------+
| 12 / 0600 |   | 13.0   | 43.6   | 1009     | 25       | tropical      |
|           |   |        |        |          |          | depression    |
+-----------+---+--------+--------+----------+----------+---------------+
| 12 / 1200 |   | 13.0   | 44.3   | 1008     | 30       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 12 / 1800 |   | 13.1   | 45.1   | 1007     | 30       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 13 / 0000 |   | 13.4   | 45.9   | 1006     | 30       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 13 / 0600 |   | 13.7   | 46.7   | 1005     | 35       | tropical      |
|           |   |        |        |          |          | storm         |
+-----------+---+--------+--------+----------+----------+---------------+
| 13 / 1200 |   | 14.1   | 47.5   | 1005     | 35       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 13 / 1800 |   | 14.4   | 48.1   | 1004     | 35       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 14 / 0000 |   | 14.7   | 48.6   | 1002     | 35       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 14 / 0600 |   | 15.0   | 49.3   | 1003     | 35       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 14 / 1200 |   | 15.3   | 49.9   | 1004     | 40       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 14 / 1800 |   | 15.6   | 50.5   | 1004     | 40       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 15 / 0000 |   | 15.9   | 51.2   | 1005     | 35       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 15 / 0600 |   | 16.2   | 52.2   | 1005     | 35       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 15 / 1200 |   | 16.3   | 53.3   | 1005     | 35       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 15 / 1800 |   | 16.5   | 54.4   | 1006     | 30       | tropical      |
|           |   |        |        |          |          | depression    |
+-----------+---+--------+--------+----------+----------+---------------+
| 16 / 0000 |   | 16.7   | 55.4   | 1006     | 30       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 16 / 0600 |   | 16.9   | 56.3   | 1006     | 30       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 16 / 1200 |   | 17.1   | 57.2   | 1006     | 30       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 16 / 1800 |   | 17.2   | 58.1   | 1007     | 30       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 17 / 0000 |   | 17.3   | 59.0   | 1009     | 25       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 17 / 0600 |   | 17.5   | 59.9   | 1010     | 25       | remnant low   |
+-----------+---+--------+--------+----------+----------+---------------+
| 17 / 1200 |   | 18.0   | 60.6   | 1010     | 25       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 17 / 1800 |   | 18.4   | 61.0   | 1010     | 25       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 18 / 0000 |   | 18.8   | 61.4   | 1011     | 20       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 18 / 0600 |   | 19.0   | 61.7   | 1011     | 20       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 18 / 1200 |   | 19.1   | 62.0   | 1011     | 20       | \"            |
+-----------+---+--------+--------+----------+----------+---------------+
| 18 / 1800 |   |        |        |          |          | dissipated    |
+-----------+---+--------+--------+----------+----------+---------------+
| 14 / 0000 |   | 14.7   | 48.6   | 1002     | 35       | minimum       |
|           |   |        |        |          |          | pressure      |
+-----------+---+--------+--------+----------+----------+---------------+
| 14 / 1200 |   | 15.3   | 49.9   | 1004     | 40       | maximum wind  |
+-----------+---+--------+--------+----------+----------+---------------+

Number range CHAPTER

Number range CHAPTERTable 2. Preliminary track forecast evaluation
(heterogeneous sample) for Tropical Storm Ingrid, 12-17 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 remnant low stage.

+---------+--------+--------+--------+--------+--------+--------+------+
| Number  | Fo     |        |        |        |        |        |      |
| range   | recast |        |        |        |        |        |      |
| C       | Period |        |        |        |        |        |      |
| HAPTERF | (h)    |        |        |        |        |        |      |
| orecast |        |        |        |        |        |        |      |
| Te      |        |        |        |        |        |        |      |
| chnique |        |        |        |        |        |        |      |
+=========+========+========+========+========+========+========+======+
|         | 12     | 24     | 36     | 48     | 72     | 96     | 120  |
+---------+--------+--------+--------+--------+--------+--------+------+
| CLP5    | 32     | 60     | 95     | 126    | **143  | 202    |      |
|         | (18)   | (16)   | (14)   | (12)   | (8)**  | (4)    |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| GFNI    | 31     | 72 (9) | 125    | 209    | 224    |        |      |
|         | (12)   |        | (9)    | (5)    | (1)    |        |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| GFDI    | 28     | 56     | 89     | 116    | **117  | **114  |      |
|         | (18)   | (16)   | (14)   | (12)   | (8)**  | (4)**  |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| HWFI    | 31 (8) | 65     | 106    | 136    | 164    | 207    |      |
|         |        | (16)   | (14)   | (12)   | (8)    | (4)    |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| GFSI    | 41     | 69     | 110    | 144    | 207    | 285    |      |
|         | (18)   | (15)   | (13)   | (11)   | (7)    | (4)    |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| AEMI    | 28     | 55     | 101    | 146    | 174    |        |      |
|         | (18)   | (16)   | (14)   | (12)   | (1)    |        |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| NGPI    | 44     | 98     | 161    | 227    | 255    | 285    |      |
|         | (16)   | (14)   | (12)   | (10)   | (5)    | (1)    |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| UKMI    | **26   | 58     | **81   | **86   | **77   | **139  |      |
|         | (16)** | (14)   | (12)** | (10)** | (6)**  | (2)**  |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| BAMD    | 52     | 101    | 148    | 184    | 254    | 377    |      |
|         | (18)   | (16)   | (14)   | (12)   | (8)    | (4)    |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| BAMM    | 28     | 58     | 100    | 141    | 211    | 299    |      |
|         | (18)   | (16)   | (14)   | (12)   | (8)    | (4)    |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| BAMS    | **25   | **48   | **85   | 117    | 179    | 234    |      |
|         | (18)** | (16)** | (14)** | (12)   | (8)    | (4)    |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| CONU    | 28     | 57     | 98     | 134    | 149    | 185    |      |
|         | (18)   | (16)   | (14)   | (12)   | (8)    | (4)    |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| GUNA    | **27   | 62     | 106    | 140    | 147    | **147  |      |
|         | (16)** | (13)   | (11)   | (9)    | (4)    | (1)**  |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| FSSE    | 37 (6) | 84 (6) | 141    | 174    | 186    |        |      |
|         |        |        | (4)    | (4)    | (1)    |        |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| OFCL    | 28     | 52     | 89     | 115    | 145    | 154    |      |
|         | (17)   | (15)   | (13)   | (11)   | (7)    | (3)    |      |
+---------+--------+--------+--------+--------+--------+--------+------+
| NHC     | 35     | 61     | 86     | 112    | 162    | 221    | 290  |
| O       | (1852) | (1686) | (1519) | (1362) | (1100) | (885)  | (    |
| fficial |        |        |        |        |        |        | 723) |
|         |        |        |        |        |        |        |      |
| (20     |        |        |        |        |        |        |      |
| 02-2006 |        |        |        |        |        |        |      |
| mean)   |        |        |        |        |        |        |      |
+---------+--------+--------+--------+--------+--------+--------+------+

Table 3. Preliminary intensity forecast evaluation (heterogeneous
sample) for Tropical Storm Ingrid, 12-17 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
remnant low stage.

+----------+-------+--------+-------+--------+-------+-------+-------+
| Number   | For   |        |       |        |       |       |       |
| range    | ecast |        |       |        |       |       |       |
| CHAPTER  | P     |        |       |        |       |       |       |
| Forecast | eriod |        |       |        |       |       |       |
| T        | (h)   |        |       |        |       |       |       |
| echnique |       |        |       |        |       |       |       |
+==========+=======+========+=======+========+=======+=======+=======+
|          | 12    | 24     | 36    | 48     | 72    | 96    | 120   |
+----------+-------+--------+-------+--------+-------+-------+-------+
| SHF5     | 2.7   | 6.1    | 9.3   | 13.8   | 19.4  | *     |       |
|          | (18)  | (16)   | (14)  | (12)   | (8)   | *26.3 |       |
|          |       |        |       |        |       | (4)** |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| GHMI     | 3.2   | **3.8  | 6.2   | **6.4  | *     | *     |       |
|          | (18)  | (16)** | (14)  | (12)** | *13.0 | *11.0 |       |
|          |       |        |       |        | (8)** | (4)** |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| HWFI     | 3.2   | 5.1    | 5.9   | 9.7    | *     | *     |       |
|          | (18)  | (16)   | (14)  | (12)   | *14.6 | *21.5 |       |
|          |       |        |       |        | (8)** | (4)** |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| SHIP     | 2.8   | 4.7    | 7.8   | 13.3   | 24.3  | 35.5  |       |
|          | (18)  | (16)   | (14)  | (12)   | (8)   | (4)   |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| DSHP     | 2.8   | 4.7    | 7.8   | 13.3   | 24.3  | 35.5  |       |
|          | (18)  | (16)   | (14)  | (12)   | (8)   | (4)   |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| FSSE     | 2.7   | 7.0    | 12.3  | 11.0   | *     |       |       |
|          | (6)   | (6)    | (4)   | (4)    | *12.0 |       |       |
|          |       |        |       |        | (1)** |       |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| ICON     | 2.4   | **3.7  | 5.8   | 9.1    | *     | *     |       |
|          | (18)  | (16)** | (14)  | (12)   | *17.6 | *22.8 |       |
|          |       |        |       |        | (8)** | (4)** |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| OFCL     | 1.8   | 4.0    | 4.2   | 7.7    | 17.9  | 28.3  |       |
|          | (17)  | (15)   | (13)  | (11)   | (7)   | (3)   |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| NHC      | 6.4   | 9.8    | 12.0  | 14.1   | 18.3  | 19.8  | 21.8  |
| Official |       |        | (     |        | (     |       |       |
|          | \(1   | \(     | 1519) | \(     | 1100) | \(    | \(    |
| (2       | 852\) | 1686\) |       | 1362\) |       | 885\) | 723\) |
| 002-2006 |       |        |       |        |       |       |       |
| mean)    |       |        |       |        |       |       |       |
+----------+-------+--------+-------+--------+-------+-------+-------+

Number range CHAPTER

![](media/image1.wmf){width="7.872222222222222in"
height="6.121527777777778in"}

> Number range CHAPTERFigure 1. Best track positions for Tropical Storm
> Ingrid, 12-17 September 2007.
>
> Number range CHAPTER
>
> ![](media/image2.wmf){width="6.749305555555556in"
> height="4.582638888888889in"}
>
> Figure 2. Selected wind observations and best track maximum sustained
> surface wind speed curve for Tropical Storm Ingrid, 12-17 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.
>
> Number range CHAPTER
>
> ![](media/image3.wmf){width="6.749305555555556in"
> height="4.582638888888889in"}
>
> Figure 3. Selected pressure observations and best track minimum
> central pressure curve for Tropical Storm Ingrid, 12-17 September
> 2007. Number range CHAPTER