Tropical Cyclone Report

Tropical Storm Cristobal

(AL032008)

19-23 July 2008

Lixion A. Avila

National Hurricane Center

15 December 2008 (revised)

a.  Synoptic History

A trough of low pressure associated with an old frontal zone became
nearly stationary along the east coast of the United States on 15 July.
The trough extended southwestward across Florida and the eastern Gulf of
Mexico and on 16 July, an area of low pressure formed on the southern
portion of the trough near the southwest coast of Florida. The low moved
northeastward across Florida, producing heavy rains, and it became
better defined just off the Georgia coast on 17 July. The shower
activity around the low gradually increased and became more
concentrated, with ample mid-level rotation. A well-defined surface
circulation center then developed, and is estimated that a tropical
depression formed at 0000 UTC 19 July about 60 n mi east of the
Georgia/South Carolina border. The depression moved slowly toward the
northeast with most of the shower activity located to the east of the
center. The surface circulation and convection continued to become
better organized and it is estimated that by 1200 UTC 19 July the
depression strengthened to a tropical storm. Cristobal moved
northeastward very close to the Outer Banks of North Carolina but the
strongest winds remained over water to the east of the center.

The cloud pattern was unimpressive at times with very limited convection
while Cristobal continued to move toward the northeast. The cyclone
encountered a more favorable atmospheric environment and strengthened,
reaching a peak intensity of 55 knots with a minimum pressure of 998 mb
at 1200 UTC 22 July. An eye feature was observed in microwave data
around that time as shown in Fig. 1. By then, Cristobal was located
about 180 n mi southeast of Cape Cod, Massachusetts. Thereafter,
Cristobal encountered cooler waters and began to weaken. By 1200 UTC 23
July, Cristobal was absorbed by a large extratropical cyclone.

The "best track" chart of the tropical cyclone's path is given in Fig.
2, with the wind and pressure histories shown in Figs. 3 and 4,
respectively. The best track positions and intensities are listed in
Table 1.

b.  Meteorological Statistics

    Observations in Cristobal (Figs. 3 and 4) include satellite-based
    Dvorak technique intensity estimates from the Tropical Analysis and
    Forecast Branch (TAFB), the Satellite Analysis Branch (SAB), as well
    as flight-level, Stepped Frequency Microwave Radiometer (SFMR) and
    dropwindsonde observations from flights of the 53^rd^ Weather
    Reconnaissance Squadron of the U. S. Air Force Reserve Command
    (AFRC). 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 the storm. In
    particular, a QuikSCAT pass at 1115 UTC 21 July was very useful for
    determining the intensity of Cristobal after reconnaissance flights
    were terminated.

c.  Casualty and Damage Statistics

    There are no reports of casualties associated with Cristobal.
    According to Environment Canada, while the center of Cristobal was
    still more than a day away from the Maritimes, rains moved out well
    ahead of the cyclone and became enhanced by a stalled frontal system
    over Nova Scotia. The result was intense rainfalls with the highest
    accumulations confined to the Atlantic coast of Nova Scotia.
    Although strong winds remained offshore and were confined to a tight
    core around the storm, the East Scotia Slope NOMAD buoy (44137)
    reported a wind gust of 50 kt. Following that report the buoy
    stopped reporting, implying that it sustained some damage from the
    storm.

d.  Forecast and Warning Critique

    A description of the weather system from which Cristobal originated
    was included in Tropical Weather Outlook (TWO) products beginning at
    1800 UTC 17 July. The possibility of tropical cyclone formation was
    included in the TWO issued at 0000 UTC 18 June, about 24 h prior to
    genesis. However, the experimental genesis forecast probability did
    not reach the high category (\> 50%) until six hours before
    formation.

    The average official track errors for Cristobal (with number of
    cases in parenthesis) were 28 (16), 50 (14), 70 (12), 96 (10) and
    99 (6) n mi for the 12, 24, 36, 48 and 72 h forecasts, respectively.
    These errors are lower than the average long-term official track
    errors as indicated in Table 2.

    Average official intensity errors were 6, 7, 6, 8 and 11 kt for the
    12, 24, 36, 48 and 72h forecasts, respectively. For comparison, the
    average long-term official intensity errors are 7, 10, 12, 14 and 18
    kt respectively.

    Due to Cristobal's proximity to the coast and the extension of the
    34-knot wind radii a tropical storm warning was issued for a portion
    of the U.S. coast from South Santee River South Carolina to the
    North Carolina/Virginia Border, including Pamlico Sound, at 0300 UTC
    19 July. The warning was discontinued at 0300 UTC 20 July when
    Cristobal moved away from the coast. There were no reports of
    tropical storm winds on land.

Table 1. Best track for Tropical Storm Cristobal, 19-23 July 2008.

+---------+-----------+-----------+-----------+--------+---------------+
| Da      | Latitude  | Longitude | Pressure  | Wind   | Stage         |
| te/Time |           |           |           | Speed  |               |
|         | \(N\)     | \(W\)     | (mb)      |        |               |
| (UTC)   |           |           |           | (kt)   |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 19 /    | 31.7      | 79.8      | 1010      | 25     | tropical      |
| 0000    |           |           |           |        | depression    |
+---------+-----------+-----------+-----------+--------+---------------+
| 19 /    | 32.2      | 79.4      | 1009      | 25     | \"            |
| 0600    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 19 /    | 32.4      | 78.8      | 1007      | 35     | tropical      |
| 1200    |           |           |           |        | storm         |
+---------+-----------+-----------+-----------+--------+---------------+
| 19 /    | 32.8      | 78.2      | 1006      | 45     | \"            |
| 1800    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 20 /    | 33.2      | 77.8      | 1006      | 45     | \"            |
| 0000    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 20 /    | 33.7      | 77.4      | 1006      | 45     | \"            |
| 0600    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 20 /    | 34.1      | 76.7      | 1006      | 45     | \"            |
| 1200    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 20 /    | 34.5      | 76.1      | 1007      | 45     | \"            |
| 1800    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 21 /    | 34.9      | 75.4      | 1005      | 50     | \"            |
| 0000    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 21 /    | 35.6      | 74.3      | 1004      | 55     | \"            |
| 0600    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 21 /    | 36.2      | 73.2      | 1000      | 55     | \"            |
| 1200    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 21 /    | 36.8      | 72.0      | 1000      | 55     | \"            |
| 1800    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 22 /    | 37.4      | 70.7      | 1000      | 55     | \"            |
| 0000    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 22 /    | 38.4      | 69.2      | 1000      | 55     | \"            |
| 0600    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 22 /    | 40.0      | 67.0      | 998       | 55     | \"            |
| 1200    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 22 /    | 41.7      | 64.2      | 1000      | 50     | \"            |
| 1800    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 23 /    | 43.3      | 60.7      | 1001      | 45     | \"            |
| 0000    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 23 /    | 44.4      | 57.5      | 1004      | 40     | \"            |
| 0600    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 23 /    |           |           |           |        | absorbed      |
| 1200    |           |           |           |        |               |
+---------+-----------+-----------+-----------+--------+---------------+
| 22 /    | 40.0      | 67.0      | 998       | 55     | Minimum       |
| 1200    |           |           |           |        | pressure      |
+---------+-----------+-----------+-----------+--------+---------------+

Table 2. Track forecast evaluation (heterogeneous sample) for Tropical
Storm Cristobal 19-23 July 2008. Forecast errors (n mi) are followed by
the number of forecasts in parentheses. Errors smaller than the NHC
official forecast are shown in boldface type.

+-----------+-------+-------+-------+-------+-------+-------+-------+
| Forecast  | For   |       |       |       |       |       |       |
| Technique | ecast |       |       |       |       |       |       |
|           | P     |       |       |       |       |       |       |
|           | eriod |       |       |       |       |       |       |
|           | (h)   |       |       |       |       |       |       |
+===========+=======+=======+=======+=======+=======+=======+=======+
|           | 12    | 24    | 36    | 48    | 72    | 96    |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CLP5      | 34    | 76    | 117   | 159   | 250 ( | 478 ( |       |
|           | (16)  | (14)  | (12)  | (10)  | 6)    | 2)    |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFNI      | 45    | 84    | 127 ( | 184 ( |       |       |       |
|           | (13)  | (11)  | 9)    | 4)    |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDI      | 36    | 63    | 93    | 105 ( | 191 ( |       |       |
|           | (16)  | (14)  | (12)  | 6)    | 2)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| HWFI      | 35    | 63    | 96    | 137 ( | 176 ( | 219 ( |       |
|           | (16)  | (14)  | (12)  | 9)    | 5)    | 1)    |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFSI      | 32    | 59    | 91    | 119   | 212 ( |       |       |
|           | (15)  | (14)  | (12)  | (10)  | 4)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| AEMI      | 44    | 70    | 92    | 117 ( | 199 ( |       |       |
|           | (16)  | (14)  | (12)  | 9)    | 1)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NGPI      | 30    | 64    | 103   | 148 ( | 219 ( |       |       |
|           | (15)  | (13)  | (11)  | 9)    | 2)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| UKMI      | 29    | **36  | **64  | 118 ( | 374 ( | 379 ( |       |
|           | (13)  | (     | (     | 7)    | 3)    | 1)    |       |
|           |       | 11**) | 9)**  |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMD      | 40    | 66    | 83    | 123   | 327 ( | 780 ( |       |
|           | (16)  | (14)  | (12)  | (10)  | 6)    | 2)    |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMM      | 39    | 57    | 85    | 111   | 257 ( | 622 ( |       |
|           | (16)  | (14)  | (12)  | (10)  | 6)    | 2)    |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMS      | 49    | 71    | 100   | 114   | 272 ( | 686 ( |       |
|           | (16)  | (14)  | (12)  | (10)  | 6)    | 2)    |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| TVCN      | 30    | 50    | 73    | **93  | 142 ( | 163 ( |       |
|           | (16)  | (14)  | (12)  | (     | 5)    | 1)    |       |
|           |       |       |       | 10)** |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GUNA      | 31    | 51 (  | 83 (  | 136 ( |       |       |       |
|           | (11)  | 9)    | 8)    | 2)    |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| FSSE      | 31    | 55    | 87 (  | 119 ( | 178 ( |       |       |
|           | (13)  | (11)  | 9)    | 7)    | 3)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | 28    | 50    | 70    | 96    | 99 (  |       |       |
|           | (16)  | (14)  | (12)  | (10)  | 6)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 34.0  | 58.2  | 82.2  | 106.2 | 154.2 | 207.5 | 272.5 |
| Official  | (     | (     | (     | (     | (996) | (787) | (627) |
|           | 1742) | 1574) | 1407) | 1254) |       |       |       |
| (         |       |       |       |       |       |       |       |
| 2003-2007 |       |       |       |       |       |       |       |
| mean)     |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

![](media/image1.jpeg){width="4.166666666666667in"
height="4.166666666666667in"}

Figure 1. Composite SSMIS 91 GHz passive microwave images of Tropical
Storm Cristobal at 1013 UTC 22 July 2008. The image shows the eye
feature marked by an arrow. Image courtesy of the Navy Research
Laboratory (NRL)

![](media/image2.jpeg){width="6.489583333333333in"
height="5.014583333333333in"}

Figure 2. Best track positions for Tropical Storm Cristobal, 19-23 July
2008.

![](media/image3.wmf){width="6.499305555555556in"
height="4.404861111111111in"}

Figure 3. Selected wind observations and best track maximum sustained
surface wind speed curve for Tropical Storm Cristobal, 19-23 July 2008.

![](media/image4.wmf){width="6.49375in" height="4.409722222222222in"}

Figure 4. Selected pressure observations and best track minimum central
pressure curve for Tropical Storm Cristobal, 19-23 July 2008.