Tropical Cyclone Report

Tropical Storm Alvin

(EP012007)

27-31 May 2007

Lixion A. Avila

National Hurricane Center

2 October 2007

This was corrected on 2 October 2007 to modify the best track for 0600
UTC 1 June when the system was a remnant low.

Alvin, the first tropical storm of eastern North Pacific season, spent
its life at sea.

Synoptic History

Alvin developed from a poorly-defined tropical wave that crossed Dakar,
Senegal on 9 May. The wave moved westward across the Atlantic Ocean and
the Caribbean Sea, with very little associated thunderstorm activity
until the wave reached Central America on 20 May. The wave continued
westward across the eastern North Pacific with a gradual increase in the
associated shower activity and developed an exposed surface circulation
center. The convection became a little better organized and it is
estimated that a tropical depression formed at 0000 UTC 27 May about 300
n mi south of the southern tip of Baja California.

There was little change in the depression's organization during the next
day or so while it moved slowly westward, with its center continuing to
be to be displaced from the convection. A small relaxation of the
easterly shear resulted in slight strengthening, and the cyclone became
a tropical storm at 0000 UTC 29 May. It reached its peak intensity of 35
knots and a minimum pressure of 1003 mb at 1200 UTC that day.
Thereafter, Alvin weakened as it moved westward into an environment of
stable air and higher shear. It is estimated that the cyclone became a
remnant low at 0000 UTC 1 June. During the next few days, Alvin's
remnants were steered by the low-level flow on a general
west-southwestward and westward track. The remnant low dissipated at
1800 UTC 6 June.

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 Alvin (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 imagery from polar-orbiting satellite were also useful in
    tracking Alvin.

c\. Casualty and Damage Statistics

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

d\. Forecast and Warning Critique

The description of the disturbance from which Alvin originated was
included in Tropical Weather Outlooks (TWO) products beginning on 24
May. The possibility of tropical cyclone formation was included in the
TWO issued at 1700 UTC 25 May, about 30 h prior to genesis.

Average official track errors (with the number of cases in parentheses)
for Alvin were 32 (18), 53 (16), 71 (14), 90 (12), 91 (8) and 139 (4) n
mi for the 12, 24, 36, 48, 72, and 96 h forecasts, respectively. These
errors are below the average official track errors for the 5-yr period
2002-2006 of 33, 57, 79, 99, 140, and 188 n mi, respectively. Table 2
displays the forecast track model statistics and shows a comparison with
the official forecast track and the 5-year official mean error.

Average official intensity errors were 3, 6, 11, 13, 17, and 25 knots
for the 12, 24, 36, 48, 72, and 96 h forecasts, respectively. The
long-term average official intensity errors are 6, 11, 15, 17, 19, and
19 knots 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 Alvin.

Table 1. Best track for Tropical Storm Alvin, 27 -31 May 2007.

+-----------+-----------+---------+---------+---------+--------------+
| Date/Time | Latitude  | Lo      | P       | Wind    | Stage        |
|           |           | ngitude | ressure | Speed   |              |
| (UTC)     | (°N)      |         |         |         |              |
|           |           | (°W)    | (mb)    | (kt)    |              |
+-----------+-----------+---------+---------+---------+--------------+
| 27 / 0000 | 12.8      | 110.6   | 1006    | 30      | tropical     |
|           |           |         |         |         | depression   |
+-----------+-----------+---------+---------+---------+--------------+
| 27 / 0600 | 13.0      | 110.9   | 1006    | 30      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 27 / 1200 | 13.1      | 111.0   | 1006    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 27 / 1800 | 13.1      | 111.1   | 1007    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 28 / 0000 | 13.1      | 111.6   | 1007    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 28 / 0600 | 13.1      | 112.2   | 1006    | 30      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 28 / 1200 | 13.0      | 112.6   | 1005    | 30      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 28 / 1800 | 12.9      | 112.8   | 1005    | 30      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 29 / 0000 | 12.8      | 113.1   | 1004    | 35      | tropical     |
|           |           |         |         |         | storm        |
+-----------+-----------+---------+---------+---------+--------------+
| 29 / 0600 | 12.7      | 113.3   | 1004    | 35      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 29 / 1200 | 12.7      | 113.5   | 1003    | 35      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 29 / 1800 | 12.8      | 113.8   | 1004    | 35      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 30 / 0000 | 12.9      | 114.1   | 1004    | 35      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 30 / 0600 | 13.1      | 114.3   | 1005    | 30      | tropical     |
|           |           |         |         |         | depression   |
+-----------+-----------+---------+---------+---------+--------------+
| 30 / 1200 | 13.3      | 114.5   | 1005    | 30      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 30 / 1800 | 13.3      | 114.8   | 1005    | 30      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 31 / 0000 | 13.2      | 115.0   | 1005    | 30      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 31 / 0600 | 13.1      | 115.2   | 1006    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 31 / 1200 | 13.0      | 115.6   | 1007    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 31 / 1800 | 12.8      | 116.0   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 01 / 0000 | 12.8      | 116.4   | 1008    | 25      | low          |
+-----------+-----------+---------+---------+---------+--------------+
| 01 /0600  | 12.7      | 117.0   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 01 / 1200 | 12.5      | 117.5   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 01 / 1800 | 12.3      | 117.9   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 02 / 0000 | 12.1      | 118.3   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 02 / 0600 | 12.0      | 118.8   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 02 / 1200 | 11.6      | 119.4   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 02 / 1800 | 11.3      | 119.8   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 03 / 0000 | 11.1      | 120.2   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 03 / 0600 | 11.0      | 120.6   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 03 / 1200 | 10.8      | 121.0   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 03 / 1800 | 10.7      | 121.3   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 04 / 0000 | 10.7      | 121.8   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 04 / 0600 | 10.7      | 122.5   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 04 / 1200 | 10.7      | 123.2   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 04 / 1800 | 10.6      | 124.0   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 05 / 0000 | 10.5      | 124.7   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 05 / 0600 | 10.6      | 125.2   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 05 / 1200 | 10.8      | 125.7   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 05 / 1800 | 10.9      | 126.1   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 06 / 0000 | 10.9      | 126.5   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 06 / 0600 | 11.0      | 127.0   | 1008    | 25      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 06 / 1200 | 11.1      | 127.4   | 1008    | 20      | \"           |
+-----------+-----------+---------+---------+---------+--------------+
| 06 / 1800 |           |         |         |         | dissipated   |
+-----------+-----------+---------+---------+---------+--------------+
| 29 / 1200 | 12.7      | 113.5   | 1003    | 35      | minimum      |
|           |           |         |         |         | pressure     |
+-----------+-----------+---------+---------+---------+--------------+

Table. 2. Preliminary forecast evaluation (heterogeneous sample) for
Tropical Storm Alvin, 27 - 31 May 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.

<table>
<colgroup>
<col style="width: 14%" />
<col style="width: 2%" />
<col style="width: 12%" />
<col style="width: 2%" />
<col style="width: 12%" />
<col style="width: 2%" />
<col style="width: 12%" />
<col style="width: 2%" />
<col style="width: 12%" />
<col style="width: 14%" />
<col style="width: 14%" />
</colgroup>
<thead>
<tr class="header">
<th rowspan="2">Forecast Technique</th>
<th colspan="10">Forecast Period (h)</th>
</tr>
<tr class="odd">
<th colspan="2">12</th>
<th colspan="2">24</th>
<th colspan="2">36</th>
<th colspan="2">48</th>
<th>72</th>
<th>96</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td colspan="2">CLP5</td>
<td colspan="2">38 (18)</td>
<td colspan="2">75 (16)</td>
<td colspan="2">114 (14)</td>
<td>154 (12)</td>
<td>276 ( 8)</td>
<td>331 ( 4)</td>
</tr>
<tr class="even">
<td colspan="2">GFNI</td>
<td colspan="2"><strong>25 (15)</strong></td>
<td colspan="2"><strong>37 (11)</strong></td>
<td colspan="2">74 ( 9)</td>
<td><strong>62 ( 4)</strong></td>
<td>111 ( 1)</td>
<td></td>
</tr>
<tr class="odd">
<td colspan="2">GFDI</td>
<td colspan="2">37 (18)</td>
<td colspan="2">68 (16)</td>
<td colspan="2">95 (14)</td>
<td>109 (12)</td>
<td>121 ( 8)</td>
<td><strong>106 ( 4)</strong></td>
</tr>
<tr class="even">
<td colspan="2">GFDN</td>
<td colspan="2">32 (16)</td>
<td colspan="2"><strong>36 (12</strong>)</td>
<td colspan="2"><strong>41 ( 7)</strong></td>
<td><strong>50 ( 4)</strong></td>
<td><strong>64 ( 2)</strong></td>
<td></td>
</tr>
<tr class="odd">
<td colspan="2">GFSI</td>
<td colspan="2">45 (15)</td>
<td colspan="2">59 (13)</td>
<td colspan="2">68 (11)</td>
<td>109 ( 9)</td>
<td>187 ( 4)</td>
<td>240 ( 1)</td>
</tr>
<tr class="even">
<td colspan="2">AEMI</td>
<td colspan="2">33 (17)</td>
<td colspan="2"><strong>50 (15)</strong></td>
<td colspan="2"><strong>52 (13)</strong></td>
<td><strong>64 (11)</strong></td>
<td>111 ( 7)</td>
<td>146 ( 3)</td>
</tr>
<tr class="odd">
<td colspan="2">NGPI</td>
<td colspan="2"><strong>31 (15)</strong></td>
<td colspan="2"><strong>49 (13)</strong></td>
<td colspan="2"><strong>53 (11)</strong></td>
<td><strong>66 ( 9)</strong></td>
<td>114 ( 5)</td>
<td><strong>94 ( 1)</strong></td>
</tr>
<tr class="even">
<td colspan="2">UKMI</td>
<td colspan="2">43 (17)</td>
<td colspan="2">100 (15)</td>
<td colspan="2">220 (13)</td>
<td>442 (11)</td>
<td><strong>83 ( 4</strong>)</td>
<td><strong>86 ( 1)</strong></td>
</tr>
<tr class="odd">
<td colspan="2">BAMD</td>
<td colspan="2">74 (18)</td>
<td colspan="2">141 (16)</td>
<td colspan="2">219 (14)</td>
<td>297 (12)</td>
<td>409 ( 8)</td>
<td>527 ( 4)</td>
</tr>
<tr class="even">
<td colspan="2">BAMM</td>
<td colspan="2">66 (18)</td>
<td colspan="2">124 (16)</td>
<td colspan="2">184 (14)</td>
<td>245 (12)</td>
<td>349 ( 8)</td>
<td>449 ( 4)</td>
</tr>
<tr class="odd">
<td colspan="2">BAMS</td>
<td colspan="2">60 (18)</td>
<td colspan="2">117 (16)</td>
<td colspan="2">168 (14)</td>
<td>215 (12)</td>
<td>306 ( 8)</td>
<td>300 ( 4)</td>
</tr>
<tr class="even">
<td colspan="2">CONU</td>
<td colspan="2"><strong>29 (17)</strong></td>
<td colspan="2">54 (15)</td>
<td colspan="2">92 (13)</td>
<td>173 (11)</td>
<td><strong>78 ( 7)</strong></td>
<td><strong>72 ( 1)</strong></td>
</tr>
<tr class="odd">
<td colspan="2">GUNA</td>
<td colspan="2"><strong>31 (15)</strong></td>
<td colspan="2"><strong>51 (13)</strong></td>
<td colspan="2"><strong>70 (11)</strong></td>
<td>101 ( 9)</td>
<td><strong>67 ( 3)</strong></td>
<td><strong>72 ( 1)</strong></td>
</tr>
<tr class="even">
<td colspan="2">FSSE</td>
<td colspan="2">38 ( 7)</td>
<td colspan="2">63 ( 6)</td>
<td colspan="2">77 ( 6)</td>
<td>128 ( 4)</td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td colspan="2">OFCL</td>
<td colspan="2">32 (18)</td>
<td colspan="2">53 (16)</td>
<td colspan="2">71 (14)</td>
<td>90 (12)</td>
<td>91 ( 8)</td>
<td>139 ( 4)</td>
</tr>
<tr class="even">
<td colspan="2"><p>NHC Official</p>
<p>(2002-2006 mean)</p></td>
<td colspan="2">33 (1349)</td>
<td colspan="2">57 (1192)</td>
<td colspan="2">79 (1039)</td>
<td>99 (897)</td>
<td>140 (655)</td>
<td>188 (465)</td>
</tr>
</tbody>
</table>

Table 3. Preliminary intensity forecast evaluation (heterogeneous
sample) for Tropical Storm Alvin, 27-31 May 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.

+--------+--------+--------+----------+--------+----------+----------+
| Fo     | Fo     |        |          |        |          |          |
| recast | recast |        |          |        |          |          |
| Tec    | Period |        |          |        |          |          |
| hnique | (h)    |        |          |        |          |          |
+--------+--------+--------+----------+--------+----------+----------+
|        | 12     | 24     | 36       | 48     | 72       | 96       |
+--------+--------+--------+----------+--------+----------+----------+
| SHF5   | 5      | 6.8    | 9.7 (14) | 11.8   | 14.3 (   | 18.5 (   |
|        | .0(18) | (16)   |          | (12)   | 8)       | 4)       |
+--------+--------+--------+----------+--------+----------+----------+
| GFDI   | 4      | **4.6  | **6.8    | **10.1 | 19.3 (   | **23.8 ( |
|        | .0(18) | (16**) | (14)**   | (12)** | 8)       | 4)**     |
+--------+--------+--------+----------+--------+----------+----------+
| SHIP   | 5.8    | 9.4    | 13.1     | 15.3   | **15.8 ( | **16.8 ( |
|        | (18)   | (16)   | (14)     | (12)   | 8)**     | 4)**     |
+--------+--------+--------+----------+--------+----------+----------+
| DSHP   | 5.8    | 9.4    | 13.1 14) | 15.3   | **15.8 ( | **16.8 ( |
|        | (18)   | (16)   |          | (12)   | 8)**     | 4)**     |
+--------+--------+--------+----------+--------+----------+----------+
| FSSE   | 4.6 (  | 10.5 ( | 14.7 (   | 18.0 ( |          |          |
|        | 7)     | 6)     | 6)       | 4)     |          |          |
+--------+--------+--------+----------+--------+----------+----------+
| ICON   | 4.5    | 7.6    | 13.4     | 16.8   | 21.5 (   | 25.0 (   |
|        | (18)   | (16)   | (14)     | (12)   | 8)       | 4)       |
+--------+--------+--------+----------+--------+----------+----------+
| OFCL   | 2.8    | 6.3    | 11.4     | 13.3   | 16.9 (   | 25.0 (   |
|        | (18)   | (16)   | (14)     | (12)   | 8)       | 4)       |
+--------+--------+--------+----------+--------+----------+----------+
| NHC    | 6.3    | 11.0   | 14.6     | 16.9   | 18.9     | 18.5     |
| Of     | (1349) | (1192) | (1039)   | (896)  | (655)    | (465)    |
| ficial |        |        |          |        |          |          |
|        |        |        |          |        |          |          |
| (200   |        |        |          |        |          |          |
| 2-2006 |        |        |          |        |          |          |
| mean)  |        |        |          |        |          |          |
+--------+--------+--------+----------+--------+----------+----------+

![](media/image1.wmf){width="6.493055555555555in"
height="5.052777777777778in"}

Figure 1. Best track positions for Tropical Storm Alvin, 27 -31 May
2007.

![](media/image2.wmf){width="6.49375in" height="4.5152777777777775in"}

Figure 2. Selected wind observations and best track maximum sustained
surface wind speed curve for Tropical Storm Alvin, 27 -31 May 2007.

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

Figure 3. Selected pressure observations and best track minimum central
pressure curve for Tropical Storm Alvin, 27 -31 May 2007.