Tropical Cyclone Report

Tropical Storm Eugene

18-20 July 2005

Richard J. Pasch

National Hurricane Center

5 April 2006

Eugene was a short-lived tropical storm that briefly threatened southern
Baja California.

a.  Synoptic History

    A tropical wave that entered the Caribbean Sea on 10 July probably
    spawned Eugene. This system continued westward, and it entered the
    eastern North Pacific by 14 July. Deep convection associated with
    the wave was disorganized as it moved generally westward to the
    south of Central America and Mexico for the next few days. By 17
    July, cloudiness became consolidated a few hundred miles to the
    south-southeast of Manzanillo, Mexico, and Dvorak classifications
    were initiated around 0000 UTC 18 July. Over the next several hours,
    deep convection became more concentrated into a circularly-shaped
    cloud mass and some banding features formed. It is estimated that
    the system developed into a tropical depression around 0600 UTC 18
    July while centered about 265 n mi south of Manzanillo. Based on
    increased organization of the cloud pattern, and a ship report (see
    next section), it is estimated that the system strengthened into a
    tropical storm by 1200 UTC 18 July. Vertical wind shear was light
    and sea-surface temperatures were higher than 27C, and these factors
    enabled the storm to gradually strengthen over the next day or so.

    A mid-level ridge over Mexico contributed to a steering current that
    directed the tropical on a northwestward heading, roughly parallel
    to the coast of Mexico, throughout its existence. Eugene reached its
    estimated peak intensity of 60 kt, at 1800 UTC 19 July while
    centered about 180 n mi west-southwest of Cabo Corrientes, Mexico.
    Eugene was already beginning to encounter cooler waters by this
    time, however, and a weakening trend was underway by 0000 UTC 20
    July. As it passed about 100 n mi to the southwest of Cabo San Lucas
    later that day, the cyclone weakened to a tropical depression.
    Eugene continued to deteriorate and by 0000 UTC 21 July it had
    degenerated to a swirl of low clouds with little or no deep
    convection. The remnant low continued northwestward for another day
    and lost its identity around 0000 UTC 22 July.

    A "best track" map of Eugene'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 Eugene (Figs. 2 and 3) include satellite-based
    Dvorak technique intensity estimates from the Tropical Analysis and
    Forecast Branch (TAFB), the Satellite Analysis Branch (SAB) and
    the U. S. Air Force Weather Agency (AFWA). The maximum intensity of
    Eugene, 60 kt, is based on a blend of Dvorak estimates from the
    above three agencies. 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 were also valuable for tracking
    and analyzing the structure of Eugene.

    There were no ship reports of winds of tropical storm force
    associated with Eugene. However, an observation of
    west-northwesterly winds of 30 kt near the cyclone center from a
    vessel with call sign MSTM6 at 1200 UTC 18 July was instrumental for
    designating the system as a tropical storm at that time.

c.  Casualty and Damage Statistics

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

d.  Forecast and Warning Critique

    Tropical Weather Outlooks (TWOs) from the National Hurricane Center
    began mentioning the area of disturbed weather that became Eugene
    about 20 h prior to tropical cyclone formation. At first, only slow
    development was expected. The potential for tropical cyclone
    formation was acknowledged in the TWO only about 8 h before the
    occurrence of the event.

Since Eugene was so short-lived, there were too few official forecasts
available to produce meaningful track or intensity verification
statistics. The mean official track errors were larger than average
through 48 h (there were no forecasts verifying beyond 48 h) and there
was a south-southwestward bias in the official track forecasts. The
official intensity forecasts correctly predicted that Eugene would
strengthen only modestly, not become a hurricane, and be a relatively
short-lived tropical cyclone.

A tropical storm watch was issued for southern Baja California (Table
2), since Eugene's outer circulation was deemed likely to come rather
close to that land area. This watch was discontinued 12 h later since
the tropical cyclone was weakening rapidly and no longer posed a
significant threat to the Baja peninsula.

Table 1. Best track for Tropical Storm Eugene, 18-20 July 2005.

+-----------+--------+---------+---------+-----------+----------------+
| Date/Time | La     | Lo      | P       | Wind      | Stage          |
|           | titude | ngitude | ressure | Speed     |                |
| (UTC)     |        |         |         |           |                |
|           | \(N\)  | \(W\)   | (mb)    | (kt)      |                |
+-----------+--------+---------+---------+-----------+----------------+
| 18 / 0600 | 14.8   | 103.7   | 1002    | 30        | tropical       |
|           |        |         |         |           | depression     |
+-----------+--------+---------+---------+-----------+----------------+
| 18 / 1200 | 15.2   | 104.3   | 1000    | 35        | tropical storm |
+-----------+--------+---------+---------+-----------+----------------+
| 18 / 1800 | 15.9   | 105.0   | 1000    | 35        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 19 / 0000 | 16.8   | 105.8   | 998     | 40        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 19 / 0600 | 17.7   | 106.8   | 997     | 45        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 19 / 1200 | 18.6   | 107.7   | 994     | 50        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 19 / 1800 | 19.5   | 108.7   | 989     | 60        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 20 / 0000 | 20.2   | 109.6   | 994     | 50        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 20 / 0600 | 20.9   | 110.3   | 998     | 40        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 20 / 1200 | 21.5   | 110.9   | 1002    | 30        | tropical       |
|           |        |         |         |           | depression     |
+-----------+--------+---------+---------+-----------+----------------+
| 20 / 1800 | 22.0   | 111.5   | 1005    | 25        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 21 / 0000 | 22.5   | 112.1   | 1005    | 25        | low            |
+-----------+--------+---------+---------+-----------+----------------+
| 21 / 0600 | 23.0   | 112.7   | 1007    | 25        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 21 / 1200 | 23.5   | 113.3   | 1007    | 20        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 21 / 1800 | 23.9   | 113.8   | 1007    | 20        | \"             |
+-----------+--------+---------+---------+-----------+----------------+
| 22 / 0000 |        |         |         |           | dissipated     |
+-----------+--------+---------+---------+-----------+----------------+
| 19 / 1800 | 19.5   | 108.7   | 989     | 60        | minimum        |
|           |        |         |         |           | pressure       |
+-----------+--------+---------+---------+-----------+----------------+

Table 2. Watch and warning summary for Tropical Storm Eugene, 18-20 July
2005.

  ----------- ------------------------------ ------------------------------
  Date/Time   Action                         Location
  (UTC)                                      

  8 / 1500    Tropical Storm Watch issued    Southern Baja California south
                                             of Agua Blanca on the west
                                             coast and south of Buenavista
                                             on the east coast

  9 / 0300    Tropical Storm Watch           Southern Baja California south
              discontinued                   of Agua Blanca on the west
                                             coast and south of Buenavista
                                             on the east coast
  ----------- ------------------------------ ------------------------------

![](media/image1.wmf){width="7.70625in" height="5.996527777777778in"}

Figure 1. Best track positions for Tropical Storm Eugene, 18-20 July
2005.

![](media/image2.wmf){width="7.097222222222222in"
height="4.819444444444445in"}

Figure 2. Selected wind observations and best track maximum sustained
surface wind speed curve for Tropical Storm Eugene, 18-20 July 2005.

![](media/image3.wmf){width="7.097222222222222in"
height="4.819444444444445in"}

Figure 3. Selected pressure observations and best track minimum central
pressure curve for Tropical Storm Eugene, 18-20 July 2005.