Tropical Cyclone Report

Tropical Depression Sixteen-E

15-20 October 2005

Stacy R. Stewart

National Hurricane Center

10 November 2005

Tropical Depression Sixteen-E was a relatively long-lived tropical
cyclone, given its weak intensity, and remained over the open Pacific
Ocean during its entire lifetime.

a.  Synoptic History

    A tropical wave moved off the west coast of Africa on 28 September
    and continued its uneventful trek across the tropical Atlantic and
    northern South America for the next two weeks. On 13 October, the
    wave emerged over the eastern North Pacific Ocean, but still
    embedded within the Intertropical Convergence Zone (ITCZ). Satellite
    classifications were initiated at 0000 UTC 14 October and, at 1200
    UTC 14 October, a QuikSCAT overpass indicated a broad low-level
    cyclonic circulation had formed along the wave axis within the ITCZ.
    As deep convection continued to develop and become organized into
    tight curved bands around the center, the disturbance gradually
    moved northwestward and began to break away from the ITCZ. It is
    estimated that a tropical depression formed at 0000 UTC 15 October,
    about 360 n mi south of Acapulco, Mexico. 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 generally westward to west-northwestward at
    5-10 kt for the next 5 days as it came under the influence of deep
    easterly steering flow on the south side of the Mexican subtropical
    ridge. Deep convective bursts with cloud tops colder than -80^o^ C
    frequently occurred near the low-level center through 16 October,
    and may have resulted in the brief development of a small but
    well-defined mid-level eye-like feature (Fig 4). It is not uncommon
    for tropical storm-force winds to occur when such a feature is
    present in satellite imagery, and it is possible that the depression
    may have briefly reached tropical storm strength. However,
    increasing northeasterly to easterly upper-level shear gradually
    displaced the convection to the west of the low-level center later
    that day, and by 1800 UTC 18 October, the cyclone had degenerated
    into a non-convective low pressure system. The remnant low moved
    westward under the influence of the low-level easterly Trade Wind
    flow for the next 24 h. Early on 19 October, deep convection began
    to redevelop near the well-defined low-level center, and by 1200
    UTC, thunderstorm activity again became organized enough for the
    cyclone to be classified as a tropical depression about 675 n mi
    south-southwest of the southern tip of Baja California. A
    combination of southeasterly upper-level shear and dry
    mid-tropospheric air limited the development of deep convection to
    mainly a few curved bands in the northwestern semicircle. A QuikSCAT
    overpass at 1332 UTC 20 October indicated the low-level circulation
    had broadened and that surface winds had decreased to 25 kt.
    Weakening continued and the system degenerated into a non-convective
    low pressure system a second time by 1800 UTC that day. The remnant
    low continued to weaken and turned southwestward and was absorbed
    back into the ITCZ about 800 n mi southwest of southern Baja
    California.

b.  Meteorological Statistics

    Observations in Tropical Depression Sixteen-E (Figs. 2 and 3)
    include satellite-based Dvorak technique intensity estimates from
    the Tropical Analysis and Forecast Branch, the Satellite Analysis
    Branch and the U. S. Air Force Weather Agency (AFWA). 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
    useful in tracking Tropical Depression Sixteen-E.

    There were no ship reports of winds of tropical storm force
    associated with Tropical Depression Sixteen-E.

c.  Casualty and Damage Statistics

    There were no reports of damages or casualties associated with
    tropical Depression Sixteen-E.

d.  Forecast and Warning Critique

    Average official track errors (with the number of cases in
    parentheses) for Tropical Depression Sixteen-E were 27 (17), 49
    (15), 77 (13), 109 (12), 195 (11), 337 (6), and 497 (3) n mi for the
    12, 24, 36, 48, 72, 96, and 120 h forecasts, respectively. These
    errors are lower than, the average official track errors for the
    10-yr period 1995-2004[^1] \[37, 68, 97, 123, 175, 208, and 259 n
    mi, respectively), (Table 2)\] through 48 h, and then much higher
    the 72-, 96-, and 120-h forecast times. The first few official
    forecast tracks indicated a west-southwestward motion in
    anticipation of a strong ridge developing to the northeast of the
    cyclone and extending southwestward. Instead, the subtropical ridge
    axis remained oriented east-to-west, which kept the cyclone moving
    on west-northwestward to westward track.

    Average official intensity errors were 3, 5, 5, 7, 10, 13 and 15 kt
    for the 12, 24, 36, 48, 72, 96, and 120 h forecasts, respectively.
    These errors were lower than the average official intensity errors
    over the 10-yr period 1995-2004 of 6, 11, 14, 17, 19, 18, and 19 kt,
    respectively. The moderate east to southeasterly vertical wind shear
    conditions were correctly forecast, which resulted in only modest
    official intensity forecast errors.

Table 1. Best track for Tropical Depression Sixteen-E, 15-20 October
2005.

+----------+---+------+--------+----------+----------+-------------------+
| D        | L |      | Lon    | Pressure | Wind     | Stage             |
| ate/Time | a |      | gitude |          | Speed    |                   |
|          | t |      |        | (mb)     |          |                   |
| (UTC)    | i |      | \(W\)  |          | (kt)     |                   |
|          | t |      |        |          |          |                   |
|          | u |      |        |          |          |                   |
|          | d |      |        |          |          |                   |
|          | e |      |        |          |          |                   |
|          |   |      |        |          |          |                   |
|          | \ |      |        |          |          |                   |
|          | ( |      |        |          |          |                   |
|          | N |      |        |          |          |                   |
|          | \ |      |        |          |          |                   |
|          | ) |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 15 /     |   | 11.0 | 101.2  | 1008     | 30       | tropical          |
| 0000     |   |      |        |          |          | depression        |
+----------+---+------+--------+----------+----------+-------------------+
| 15 /     |   | 11.0 | 101.4  | 1008     | 30       | \"                |
| 0600     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 15 /     |   | 11.0 | 101.6  | 1007     | 30       | \"                |
| 1200     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 15 /     |   | 11.0 | 101.8  | 1007     | 30       | \"                |
| 1800     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 16 /     |   | 11.0 | 102.1  | 1006     | 30       | \"                |
| 0000     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 16 /     |   | 11.1 | 102.5  | 1005     | 30       | \"                |
| 0600     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 16 /     |   | 11.4 | 103.2  | 1006     | 30       | \"                |
| 1200     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 16 /     |   | 11.7 | 103.8  | 1006     | 30       | \"                |
| 1800     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 17 /     |   | 12.0 | 104.4  | 1006     | 30       | \"                |
| 0000     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 17 /     |   | 12.1 | 105.1  | 1007     | 30       | \"                |
| 0600     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 17 /     |   | 12.2 | 105.8  | 1007     | 30       | \"                |
| 1200     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 17 /     |   | 12.2 | 106.6  | 1007     | 30       | \"                |
| 1800     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 18 /     |   | 12.1 | 107.5  | 1008     | 25       | remnant low       |
| 0000     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 18 /     |   | 12.0 | 108.4  | 1008     | 25       | \"                |
| 0600     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 18 /     |   | 12.0 | 109.3  | 1008     | 25       | \"                |
| 1200     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 18 /     |   | 11.9 | 110.3  | 1008     | 25       | \"                |
| 1800     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 19 /     |   | 11.8 | 111.3  | 1008     | 25       | \"                |
| 0000     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 19 /     |   | 12.3 | 112.3  | 1008     | 25       | \"                |
| 0600     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 19 /     |   | 12.1 | 113.5  | 1007     | 30       | tropical          |
| 1200     |   |      |        |          |          | depression        |
+----------+---+------+--------+----------+----------+-------------------+
| 19 /     |   | 12.3 | 114.7  | 1007     | 30       | \"                |
| 1800     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 20 /     |   | 12.4 | 115.6  | 1007     | 30       | \"                |
| 0000     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 20 /     |   | 12.4 | 116.7  | 1007     | 30       | \"                |
| 0600     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 20 /     |   | 12.5 | 117.8  | 1007     | 30       | \"                |
| 1200     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 20 /     |   | 12.7 | 118.9  | 1008     | 25       | \"                |
| 1800     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 21 /     |   | 12.7 | 119.6  | 1009     | 25       | remnant low       |
| 0000     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 21 /     |   | 12.6 | 120.2  | 1010     | 20       | \"                |
| 0600     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+
| 21 /     |   |      |        |          |          | absorbed into     |
| 1200     |   |      |        |          |          | ITCZ              |
+----------+---+------+--------+----------+----------+-------------------+
| 16 /     |   | 11.1 | 102.5  | 1005     | 30       | minimum pressure  |
| 0600     |   |      |        |          |          |                   |
+----------+---+------+--------+----------+----------+-------------------+

Table 4. Preliminary forecast evaluation (heterogeneous sample) for
Tropical Depression

Sixteen-E, 15-20 October 2005. 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, if any.

+-----------+-------+-------+-------+-------+-------+-------+-------+
| Forecast  | For   |       |       |       |       |       |       |
| Technique | ecast |       |       |       |       |       |       |
|           | P     |       |       |       |       |       |       |
|           | eriod |       |       |       |       |       |       |
|           | (h)   |       |       |       |       |       |       |
+===========+=======+=======+=======+=======+=======+=======+=======+
|           | 12    | 24    | 36    | 48    | 72    | 96    | 120   |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CLP5      | 31    | 66    | 110   | 161   | 292   | 442 ( | 541 ( |
|           | (21)  | (19)  | (17)  | (15)  | (12)  | 8)    | 4)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFNI      | 35    | 74 (  | 121 ( | 157 ( | 204 ( | **    | 586 ( |
|           | (12)  | 9)    | 9)    | 8)    | 6)    | 285** | 2)    |
|           |       |       |       |       |       | ( 5)  |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDI      | 31    | 53    | *     | *     | **    | **    | **    |
|           | (19)  | (17)  | *71** | *92** | 142** | 193** | 193** |
|           |       |       | (15)  | (14)  | (12)  | ( 8)  | ( 4)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDL\*    | 29    | 52    | *     | *     | **    | **    | **    |
|           | (19)  | (17)  | *75** | *95** | 151** | 196** | 225** |
|           |       |       | (15)  | (13)  | (11)  | ( 8)  | ( 4)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDN\*    | 30    | 66 (  | 109 ( | 156 ( | **    | 356 ( | **    |
|           | (11)  | 9)    | 7)    | 7)    | 189** | 3)    | 435** |
|           |       |       |       |       | ( 6)  |       | ( 1)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFSI      | 35    | 69    | 111   | 149   | 249 ( | **    |       |
|           | (17)  | (15)  | (13)  | (12)  | 9)    | 336** |       |
|           |       |       |       |       |       | ( 5)  |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFSO\*    | 35    | 65    | 100   | 141   | 245   | **    | **    |
|           | (20)  | (18)  | (16)  | (13)  | (10)  | 316** | 332** |
|           |       |       |       |       |       | ( 6)  | ( 1)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| AEMI      | 31    | 58    | 88    | 118   | **    | **    | **    |
|           | (17)  | (15)  | (13)  | (12)  | 185** | 208** | 300** |
|           |       |       |       |       | ( 7)  | ( 2)  | ( 1)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NGPI      | 30    | 69    | 121   | 164   | 254   | 383 ( | **    |
|           | (17)  | (15)  | (14)  | (14)  | (12)  | 8)    | 462** |
|           |       |       |       |       |       |       | ( 4)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NGPS\*    | 35    | 63    | 107   | 145   | 210   | **    | **    |
|           | (17)  | (15)  | (13)  | (13)  | (11)  | 343** | 397** |
|           |       |       |       |       |       | ( 7)  | ( 3)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| UKMI      | 61    | 113   | 160   | 205   | 299 ( | 517 ( | 908 ( |
|           | (18)  | (16)  | (14)  | (13)  | 9)    | 5)    | 3)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| UKM\*     | 43    | 115 ( | 153 ( | 195 ( | 297 ( | 463 ( | 728 ( |
|           | (10)  | 9)    | 8)    | 7)    | 5)    | 3)    | 2)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMD      | 40    | 79    | 124   | 169   | 270   | 412 ( | 750 ( |
|           | (21)  | (19)  | (17)  | (15)  | (12)  | 8)    | 4)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMM      | *     | *     | *     | *     | *     | **    | **    |
|           | *24** | *41** | *61** | *74** | *98** | 168** | 124** |
|           | (21)  | (19)  | (17)  | (15)  | (12)  | ( 8)  | ( 4)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMS      | 30    | 49    | *     | *     | **    | **    | **    |
|           | (21)  | (19)  | *69** | *90** | 139** | 268** | 344** |
|           |       |       | (17)  | (15)  | (12)  | ( 8)  | ( 4)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CONU      | 31    | 60    | 93    | 123   | **    | **    | **    |
|           | (19)  | (17)  | (15)  | (14)  | 190** | 289** | 480** |
|           |       |       |       |       | (12)  | ( 8)  | ( 4)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GUNA      | 28    | 55    | 86    | 116   | **    | **    |       |
|           | (14)  | (12)  | (11)  | (11)  | 150** | 263** |       |
|           |       |       |       |       | ( 7)  | ( 3)  |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | 27    | 49    | 77    | 109   | 195   | 337 ( | 497 ( |
|           | (17)  | (15)  | (13)  | (12)  | (11)  | 6)    | 3)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 37    | 68    | 97    | 123   | 175   | 208   | 259   |
| Official  |       |       |       |       |       |       |       |
|           | \(2   | \(2   | \(2   | \(1   | \(1   | \(    | \(    |
| (         | 654\) | 378\) | 096\) | 829\) | 386\) | 355\) | 224\) |
| 1995-2004 |       |       |       |       |       |       |       |
| mean)     |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

\* model not available at forecast time

![](media/image1.wmf){width="6.377777777777778in"
height="4.954166666666667in"}

Figure 1. Best track positions for Tropical Depression Sixteen-E, 15-20
October 2005.

![](media/image2.wmf){width="6.4944444444444445in"
height="4.375694444444444in"}

Figure 2. Selected wind observations and best track maximum sustained
surface wind speed

curve for Tropical Depression Sixteen-E, 15-20 October 2005. Objective
Dvorak estimates

represent linear averages over a three-hour period centered on the
nominal observation time.

![](media/image3.wmf){width="6.4944444444444445in"
height="4.375694444444444in"}

Figure 3. Selected pressure observations and best track minimum central
pressure curve for Tropical Depression Sixteen-E, 15-20 October 2005.
Objective Dvorak estimates represent linear averages over a three-hour
period centered on the nominal observation time.

![](media/image4.jpeg){width="6.2555555555555555in"
height="6.2555555555555555in"}

Figure 4. A 0531 UTC 16 October 2005 NASA TRMM 85GHZ microwave satellite
image showing a small eye feature at about the time the depression was
at its peak intensity (image courtesy of the U.S. Navy FNMOC, Monterey,
CA).

[^1]: Errors given for the 96 and 120 h periods are averages over the
    four-year period 2001-4.