Number range CHAPTERTropical Cyclone Report

Tropical Storm Chantal

(AL032007)

31 July-1 August 2007

Richard J. Pasch

National Hurricane Center

18 October 2007

Chantal was a short-lived tropical storm that moved roughly parallel to,
but offshore from, the U.S. east coast.

a.  Synoptic History

    A frontal system moved off the coasts of North Carolina and South
    Carolina on 21 July. Over the next several days the front drifted
    southward and southeastward while decaying into a low-level trough,
    and had generated an area of cloudiness and convection several
    hundred miles east of northeastern Florida by 25 July. The area of
    disturbed weather drifted southward and became quasi-stationary a
    few hundred miles east of the Bahamas by 26 July. Convection was not
    very persistent over the area for the next few days, and it was not
    until 28 July that the first Dvorak classification was performed on
    this weather system. The clouds and convection did not become
    significantly better organized over the next couple of days while
    the system moved slowly northward. By 1200 UTC 30 July, visible
    satellite images showed that a surface circulation had developed,
    but the convection was too far removed from the center to justify
    designating the system as a tropical cyclone. Around 0000 UTC 31
    July, however, the low-level circulation center became well-enough
    involved with the deep convection to warrant designating the system
    as a tropical depression, while centered about 210 n mi
    north-northwest of Bermuda and about 450 n mi east of Cape Hatteras,
    North Carolina. Over the ensuing 6 to 12 h, there was an increase in
    the amount of deep convection near the center, and QuikSCAT
    scatterometer data suggest that the cyclone had strengthened into a
    tropical storm by 0600 UTC 31 July. QuikSCAT observations also
    indicate that Chantal reached its peak intensity of 45 kt by 1200
    UTC 31 July. The "best track" chart of Chantal's path is given in
    Fig. 1, with the wind and pressure time series displayed in Figs. 2
    and 3, respectively. The best track positions and intensities are
    listed in Table 1.

    During Chantal's brief existence, the primary steering feature was a
    mid-tropospheric trough situated just off the U.S. east coast. The
    flow on the eastern side of the trough drove the tropical cyclone on
    a north-northeastward to northeastward trajectory with an increasing
    forward speed of motion. By 0000 UTC 01 August, a convective band
    that had been wrapping around the center of the storm was weakening,
    and the circulation became embedded within a frontal zone,
    signifying that Chantal was losing tropical characteristics. The
    system transformed into an extratropical cyclone by 0600 UTC 1
    August, and subsequently passed over the eastern end of the Avalon
    Peninsula of Newfoundland around 1300 to 1400 UTC that day. This
    resulted in very heavy rainfall over the peninsula (see next
    section). The post-Chantal cyclone intensified to near hurricane
    force as it raced northeastward over the north Atlantic late on 1
    August and early on 2 August. Some weakening of the cyclone, with a
    considerable decrease of forward speed, occurred on 2 August but the
    extratropical storm re-intensified to near hurricane strength again
    by early on 3 August. By then the system had turned toward the east.
    The cyclone began its final weakening later on 3 August, and passed
    a couple hundred miles south and southeast of Iceland by 4 August.
    On 5 August, Chantal's extratropical remnant turned northeastward
    and merged with another extratropical cyclone several hundred miles
    east of Iceland -- and finally lost its identity.

b.  Meteorological Statistics

    Observations in Chantal (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 satellite imagery from NOAA polar-orbiting satellites, the
    NASA Tropical Rainfall Measuring Mission (TRMM), the NASA QuikSCAT,
    and Defense Meteorological Satellite Program (DMSP) satellites,
    among others, were also useful in tracking Chantal. Several QuikSCAT
    overpasses helped to assess the intensity of the tropical cyclone,
    including the maximum wind estimate of 45 kt.

    Ship reports of winds of tropical storm force associated with
    Chantal are given in Table 2.

    The post-Chantal extratropical cyclone caused very heavy rainfall
    over parts of southeastern Newfoundland. Analyses from the Canadian
    Hurricane Centre indicate that rainfall totals approached 8 inches
    over portions of the Avalon Peninsula of Newfoundland. These rains
    resulted in severe flooding over some sections of the Peninsula.

c.  Casualty and Damage Statistics

    There were no reports of damage or casualties associated with
    Chantal. However the extratropical cyclone that was formerly Chantal
    did cause some flood-related damages in southeastern Newfoundland.

d.  Forecast and Warning Critique

The disturbance that eventually formed into Chantal was first mentioned
in the Tropical Weather Outlook (TWO) issued at 1530 UTC 28 July, 56.5 h
before genesis. The TWO issued 8.5 h prior to genesis first indicated
the possibility of the system becoming a tropical or subtropical cyclone
"before merging with a frontal boundary".

Since Chantal was a tropical cyclone for only one day, none of the
official forecasts associated with the five advisories verified beyond
24 h. There were three 12-h track forecasts that had an average error of
36 n mi and one 24-h forecast that had an error of 0 n mi. The few
official intensity forecasts had errors of 10 kt or less.

Watches and/or warnings were not required for Chantal.

Number range CHAPTERTable 1. Best track for Tropical Storm Chantal, 31
July-1 August 2007.

+----------+---------+---------+---------+---------+----------------+
| D        | L       | Lo      | P       | Wind    | Stage          |
| ate/Time | atitude | ngitude | ressure | Speed   |                |
|          |         |         |         |         |                |
| (UTC)    | (°N)    | (°W)    | (mb)    | (kt)    |                |
+----------+---------+---------+---------+---------+----------------+
| 31 /     | 35.5    | 66.5    | 1007    | 30      | tropical       |
| 0000     |         |         |         |         | depression     |
+----------+---------+---------+---------+---------+----------------+
| 31 /     | 37.1    | 65.5    | 1004    | 35      | tropical storm |
| 0600     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 31 /     | 39.1    | 64.2    | 999     | 45      | \"             |
| 1200     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 31 /     | 40.7    | 62.3    | 999     | 45      | \"             |
| 1800     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 01 /     | 42.5    | 60.0    | 994     | 45      | \"             |
| 0000     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 01 /     | 44.0    | 57.5    | 992     | 45      | extratropical  |
| 0600     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 01 /     | 46.0    | 54.5    | 990     | 55      | \"             |
| 1200     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 01 /     | 49.0    | 49.5    | 988     | 60      | \"             |
| 1800     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 02 /     | 53.0    | 43.0    | 985     | 60      | \"             |
| 0000     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 02 /     | 55.5    | 38.5    | 975     | 50      | \"             |
| 0600     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 02 /     | 57.5    | 35.4    | 970     | 50      | \"             |
| 1200     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 02 /     | 58.6    | 33.9    | 967     | 55      | \"             |
| 1800     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 03 /     | 58.9    | 32.1    | 964     | 60      | \"             |
| 0000     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 03 /     | 58.9    | 30.4    | 964     | 60      | \"             |
| 0600     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 03 /     | 58.9    | 28.0    | 964     | 60      | \"             |
| 1200     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 03 /     | 58.9    | 25.2    | 967     | 55      | \"             |
| 1800     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 04 /     | 59.1    | 22.6    | 967     | 55      | \"             |
| 0000     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 04 /     | 59.5    | 19.1    | 970     | 50      | \"             |
| 0600     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 04 /     | 60.7    | 16.3    | 975     | 50      | \"             |
| 1200     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 04 /     | 61.7    | 14.0    | 978     | 45      | \"             |
| 1800     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 05 /     | 62.7    | 12.0    | 980     | 45      | \"             |
| 0000     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 05 /     | 64.0    | 9.5     | 982     | 45      | \"             |
| 0600     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 05 /     | 66.0    | 7.0     | 985     | 35      | \"             |
| 1200     |         |         |         |         |                |
+----------+---------+---------+---------+---------+----------------+
| 05 /     |         |         |         |         | merged with    |
| 1800     |         |         |         |         | another        |
|          |         |         |         |         | extratropical  |
|          |         |         |         |         | cyclone        |
+----------+---------+---------+---------+---------+----------------+
| 01 /     | 42.5    | 60.0    | 994     | 45      | minimum        |
| 0000     |         |         |         |         | pressure       |
+----------+---------+---------+---------+---------+----------------+

Number range CHAPTERTable 2. Selected ship reports with winds of at
least 34 kt for Tropical Storm Chantal, 31 July-1 August 2007.

+-----------+-----------+-----------+-----------+-----------+-----------+
| Date/Time | Ship call | Latitude  | Longitude | Wind      | Pressure  |
| (UTC)     | sign      |           |           |           |           |
|           |           | (°N)      | (°W)      | dir/speed | (mb)      |
|           |           |           |           | (kt)      |           |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 31 / 0400 | ZCDM6     | 33.9      | 65.9      | 230 / 35  | 1016.6    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 31 / 1800 | KHJB      | 38.7      | 58.7      | 190 / 42  | 1014.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 31 / 2100 | KHJB      | 38.8      | 59.4      | 180 / 43  | 1011.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 01 / 0000 | VRBN8     | 41.3      | 59.1      | 210 / 37  | 1011.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+

![](media/image1.wmf){width="7.761111111111111in"
height="5.996527777777778in"}

Number range CHAPTERFigure 1. Best track positions for Tropical Storm
Chantal, 31 July-1 August 2007. Track during the extratropical stage is
based partially on analyses from the NOAA Ocean Prediction Center.

![](media/image2.wmf){width="7.055555555555555in"
height="4.819444444444445in"}

Number range CHAPTERFigure 2. Selected wind observations and best track
maximum sustained surface wind speed curve for Tropical Storm Chantal,
31 July-1 August 2007. Estimates during the extratropical stage are
based partially on analyses from the NOAA Ocean Prediction Center.

![](media/image3.wmf){width="7.055555555555555in"
height="4.819444444444445in"}

Number range CHAPTERFigure 3. Selected pressure observations and best
track minimum central pressure curve for Tropical Storm Chantal, 31
July-1 August 2007. Estimates during the extratropical stage are based
partially on analyses from the NOAA Ocean Prediction Center.Number range
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