Tropical Cyclone Report

Hurricane Epsilon

29 November -- 8 December 2005

James L. Franklin

National Hurricane Center

7 January 2006

Epsilon, the 26^th^ named tropical cyclone of the 2005 hurricane season,
developed from a non-tropical upper-level area of low pressure in the
central subtropical Atlantic, becoming the second tropical cyclone to do
so in this area within the span of a week. It was only the sixth
hurricane on record in the month of December.

a.  Synoptic History

    Late on 27 November a surface gale center developed beneath a
    non-tropical upper-level area of low pressure about 1000 n mi east
    of Bermuda. At this time a stationary front extended from just north
    of the surface low eastward to the vicinity of Tropical Storm Delta,
    which was then beginning to lose tropical characteristics. The
    surface low began to separate from the frontal zone the following
    day, but as it did so the associated non-frontal convection was
    limited and poorly organized. Very early on 29 November, however, a
    burst of deep convection developed just north of the surface low
    center, and by 1500 UTC had wrapped completely around the center
    into a ring not more than 40 n mi across. Based on the development
    of this organized core convection, and the presumption that the
    convection was co-located with the system's radius of maximum wind,
    it is assessed that the low became a tropical storm near 0600 UTC 29
    November. 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.

    After becoming a tropical storm, Epsilon moved west-southwestward
    along the southern periphery of a high-latitude ridge. Initially,
    Epsilon was embedded within the upper low from which it formed, and
    this provided a weak-shear and unstable environment conducive to
    modest strengthening. Epsilon developed a ragged eye and its winds
    reached 55 kt on 30 November. Still embedded within the upper low,
    Epsilon then executed a cyclonic loop on 1 December with little
    change in strength as a deep-layer trough approached from the
    western Atlantic. The upper-low then weakened, leaving Epsilon in a
    light west-southwesterly flow ahead of the approaching trough.
    Moving northeastward, Epsilon strengthened over 22C waters and
    became a hurricane at 1800 UTC 2 December, about 850 n mi
    east-northeast of Bermuda.

    Epsilon turned eastward on 3 December, remaining south of the main
    belt of strong westerlies. Anticyclonic outflow developed in the
    northern semicircle and the hurricane took on an annular appearance
    with a large 30-35 n mi diameter eye. Little change in structure or
    strength occurred over the next two days as Epsilon continued
    leisurely eastward over cool waters, with Epsilon's estimated peak
    intensity of 75 kt occurring early on 5 December. Late that day, the
    frontal zone associated with the deep-layer trough passed just north
    of Epsilon, and with high pressure building behind this trough,
    Epsilon's eastward motion began to slow. Epsilon turned
    southwestward to the south of the building ridge on 6 December,
    maintaining hurricane strength along with its large eye in the
    weak-shear environment to the south of the ridge. On the following
    day, however, strong upper-level northwesterly flow swept over the
    tropical cyclone, disrupting the eye and displacing the deep
    convection to the southeast of the center. After spending five days
    as a hurricane - a record for December - Epsilon weakened to a
    tropical storm at 1800 UTC 7 December about 800 n mi southwest of
    the Azores. The strong shear continued, and stripped Epsilon of its
    deep convection early on 8 December. Epsilon weakened to a tropical
    depression at 1200 UTC that day and had degenerated to a remnant low
    by 1800 UTC. On 9 December, the remnant circulation began to
    elongate in advance of an approaching frontal zone and the
    circulation dissipated later that day.

b.  Meteorological Statistics

    Observations in Epsilon (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). 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 Epsilon.

    Prior to becoming a tropical storm, Epsilon's satellite appearance
    resembled some classic Hebert-Poteat subtropical cyclones, and a
    case can be made for classifying Epsilon as subtropical late on 28
    November. However, subtropical cyclones are by definition
    non-frontal, and it is judged here that the system did not have
    enough organized non-frontal convection prior to 0600 UTC 29
    November to consider the low either a subtropical or tropical
    cyclone.

    Epsilon's satellite presentation oscillated within a fairly narrow
    range over a 5-day period, with subjective Dvorak T-numbers ranging
    between T3.5 (55 kt) and T4.5 (77 kt). At one point during this
    time, Epsilon was operationally downgraded to a tropical storm.
    Considerable smoothing to the operational intensity estimates has
    been applied. QuikSCAT data (particularly on 2 and 3 December)
    suggest that Epsilon might have been a little weaker than assessed
    here, but due to the resolution of the instrument the data are not
    conclusive. The peak intensity is assigned to 0600-1200 UTC 5
    December, to coincide with the time of the highest objective Dvorak
    classification of T4.7. Epsilon's estimated peak wind of 75 kt is a
    little below the nominal wind corresponding to a T4.7 (Fig. 2); this
    assessment is based on the presumption that the relatively cool
    sea-surface temperatures and shallow convection might result in
    surface winds slightly lower than normal for this classification.

    There were no ship reports of winds of tropical storm force
    associated directly with the circulation of Epsilon, although there
    were reports of gales associated with the antecedent non-tropical
    area of low pressure.

c.  Casualty and Damage Statistics

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

d.  Forecast and Warning Critique

    NHC Tropical Weather Outlooks first mentioned the precursor area of
    low pressure about 30 h prior to the first advisory on Epsilon,
    indicating that the low had some potential for tropical or
    subtropical development.

    Average official track errors (with the number of cases in
    parentheses) for Epsilon were 29 (35), 53 (33), 75 (31), 94 (29),
    152 (25), 293 (21), and 544 (17) 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]
    through 72 h, and higher than the long-term means thereafter (Table
    4). The large errors at the longer ranges resulted from early
    forecasts that failed to anticipate the southwestward turn. Of the
    primary guidance models, the UKMI was the first to indicate this
    turn would occur. The BAMM also performed very well with Epsilon.

    Average official intensity errors were 8, 11, 16, 22, 23, 24, and 24
    kt for the 12, 24, 36, 48, 72, 96, and 120 h forecasts,
    respectively. For comparison, the average official intensity errors
    over the 10-yr period 1995-2004 are 6, 10, 12, 15, 18, 20, and 22
    kt, respectively. Virtually all the forecasts at 24 h and beyond had
    a significant low bias, as they consistently predicted weakening
    much earlier than what was observed. The GFDI did a good job
    forecasting that Epsilon would maintain its strength over cooler
    waters in an otherwise favorable thermodynamic environment. The
    SHIPS model, which had even larger biases than the official
    forecast, likely overestimated the actual shear directly over
    Epsilon.

Table 1. Best track for Hurricane Epsilon, 29 November - 8 December
2005.

+---------+--------+--------+--------+---------+---------------------+
| Da      | La     | Lon    | Pr     | Wind    | Stage               |
| te/Time | titude | gitude | essure | Speed   |                     |
|         |        |        |        |         |                     |
| (UTC)   | \(N\)  | \(W\)  | (mb)   | (kt)    |                     |
+---------+--------+--------+--------+---------+---------------------+
| 29 /    | 31.5   | 49.2   | 993    | 45      | tropical storm      |
| 0600    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 29 /    | 31.6   | 50.0   | 993    | 45      | \"                  |
| 1200    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 29 /    | 31.4   | 50.8   | 993    | 45      | \"                  |
| 1800    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 30 /    | 31.4   | 51.5   | 993    | 45      | \"                  |
| 0000    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 30 /    | 31.1   | 52.5   | 992    | 50      | \"                  |
| 0600    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 30 /    | 30.8   | 53.5   | 991    | 55      | \"                  |
| 1200    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 30 /    | 30.1   | 54.2   | 991    | 50      | \"                  |
| 1800    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 01 /    | 29.7   | 53.8   | 992    | 50      | \"                  |
| 0000    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 01 /    | 30.0   | 52.7   | 992    | 50      | \"                  |
| 0600    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 01 /    | 30.8   | 51.9   | 992    | 50      | \"                  |
| 1200    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 01 /    | 31.4   | 51.3   | 991    | 55      | \"                  |
| 1800    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 02 /    | 31.9   | 50.6   | 991    | 55      | \"                  |
| 0000    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 02 /    | 32.5   | 49.8   | 990    | 55      | \"                  |
| 0600    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 02 /    | 33.2   | 48.9   | 989    | 60      | \"                  |
| 1200    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 02 /    | 33.9   | 47.9   | 987    | 65      | hurricane           |
| 1800    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 03 /    | 34.3   | 47.1   | 987    | 65      | \"                  |
| 0000    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 03 /    | 34.5   | 46.2   | 987    | 65      | \"                  |
| 0600    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 03 /    | 34.5   | 45.0   | 987    | 65      | \"                  |
| 1200    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 03 /    | 34.5   | 43.7   | 987    | 65      | \"                  |
| 1800    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 04 /    | 34.3   | 42.3   | 987    | 65      | \"                  |
| 0000    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 04 /    | 34.4   | 41.1   | 987    | 65      | \"                  |
| 0600    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 04 /    | 34.3   | 39.8   | 984    | 70      | \"                  |
| 1200    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 04 /    | 34.3   | 38.8   | 985    | 70      | \"                  |
| 1800    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 05 /    | 34.2   | 37.8   | 985    | 70      | \"                  |
| 0000    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 05 /    | 34.0   | 36.7   | 981    | 75      | \"                  |
| 0600    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 05 /    | 33.8   | 35.5   | 981    | 75      | \"                  |
| 1200    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 05 /    | 33.7   | 34.6   | 985    | 70      | \"                  |
| 1800    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 06 /    | 33.4   | 33.8   | 986    | 65      | \"                  |
| 0000    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 06 /    | 33.1   | 33.7   | 986    | 65      | \"                  |
| 0600    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 06 /    | 32.3   | 33.7   | 987    | 65      | \"                  |
| 1200    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 06 /    | 31.6   | 34.2   | 987    | 65      | \"                  |
| 1800    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 07 /    | 30.8   | 34.9   | 987    | 65      | \"                  |
| 0000    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 07 /    | 30.1   | 36.0   | 987    | 65      | \"                  |
| 0600    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 07 /    | 29.4   | 37.1   | 987    | 65      | \"                  |
| 1200    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 07 /    | 28.7   | 38.1   | 991    | 60      | tropical storm      |
| 1800    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 08 /    | 28.2   | 38.8   | 997    | 50      | \"                  |
| 0000    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 08 /    | 27.4   | 39.3   | 1003   | 35      | \"                  |
| 0600    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 08 /    | 26.5   | 40.0   | 1005   | 30      | tropical depression |
| 1200    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 08 /    | 25.9   | 40.5   | 1006   | 30      | low                 |
| 1800    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 09 /    | 25.5   | 40.6   | 1007   | 30      | \"                  |
| 0000    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 09 /    | 25.1   | 40.4   | 1008   | 25      | \"                  |
| 0600    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 09 /    | 24.7   | 40.1   | 1009   | 25      | \"                  |
| 1200    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 09 /    | 24.7   | 39.2   | 1009   | 25      | \"                  |
| 1800    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 10 /    |        |        |        |         | dissipated          |
| 0000    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+
| 05 /    | 34.0   | 36.7   | 981    | 75      | minimum pressure    |
| 0600    |        |        |        |         |                     |
+---------+--------+--------+--------+---------+---------------------+

Table 2. Preliminary forecast evaluation (heterogeneous sample) for
Hurricane Epsilon, 29 November - 8 December 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. Table includes only guidance available at forecast time.

+-----------+-------+-------+-------+-------+-------+-------+-------+
| Forecast  | For   |       |       |       |       |       |       |
| Technique | ecast |       |       |       |       |       |       |
|           | P     |       |       |       |       |       |       |
|           | eriod |       |       |       |       |       |       |
|           | (h)   |       |       |       |       |       |       |
+===========+=======+=======+=======+=======+=======+=======+=======+
|           | 12    | 24    | 36    | 48    | 72    | 96    | 120   |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CLP5      | 47    | 114   | 206   | 314   | 431   | 592   | 754   |
|           | (35)  | (33)  | (31)  | (29)  | (25)  | (21)  | (17)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFNI      | 32    | 58    | 85    | 120   | 234   | 424   | 569   |
|           | (33)  | (31)  | (29)  | (27)  | (23)  | (19)  | (13)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDI      | **27  | **47  | **69  | 96    | 188   | 405   | 687   |
|           | (     | (     | (     | (28)  | (23)  | (19)  | (13)  |
|           | 34)** | 32)** | 30)** |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFSI      | 29    | **48  | **61  | **85  | 160   | 299   | 561   |
|           | (34)  | (     | (     | (     | (23)  | (18)  | (12)  |
|           |       | 32)** | 30)** | 28)** |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| AEMI      | **27  | **45  | **63  | **91  | 187   | 338   | **438 |
|           | (     | (     | (     | (     | (24)  | (20)  | (     |
|           | 34)** | 32)** | 30)** | 28)** |       |       | 16)** |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NGPI      | 35    | 61    | 90    | 119   | 205   | **275 | **320 |
|           | (34)  | (32)  | (30)  | (28)  | (24)  | (     | (     |
|           |       |       |       |       |       | 20)** | 16)** |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| UKMI      | 45    | 82    | 119   | 150   | 179   | **223 | **292 |
|           | (32)  | (30)  | (28)  | (24)  | (16)  | (     | (     |
|           |       |       |       |       |       | 12)** | 6)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| A98E      | 43    | 95    | 141   | 189   | 285   | 406   | 566   |
|           | (35)  | (33)  | (31)  | (29)  | (25)  | (21)  | (17)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| A9UK      | 46    | 112   | 184   | 240   | 323   |       |       |
|           | (18)  | (17)  | (16)  | (15)  | (13)  |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMD      | 59    | 112   | 153   | 186   | 304   | 601   | 1133  |
|           | (34)  | (32)  | (30)  | (28)  | (25)  | (21)  | (17)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMM      | **28  | 54    | 77    | 94    | **142 | **194 | **266 |
|           | (     | (33)  | (31)  | (29)  | (     | (     | (     |
|           | 35)** |       |       |       | 25)** | 21)** | 17)** |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMS      | 42    | 78    | 119   | 156   | 214   | **218 | **206 |
|           | (35)  | (33)  | (31)  | (29)  | (25)  | (     | (     |
|           |       |       |       |       |       | 21)** | 17)** |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CONU      | 29    | **50  | **73  | 96    | 182   | 312   | **450 |
|           | (34)  | (     | (     | (28)  | (24)  | (20)  | (     |
|           |       | 32)** | 30)** |       |       |       | 16)** |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GUNA      | 30    | **51  | **71  | 94    | **142 | **279 | 567 ( |
|           | (32)  | (     | (     | (24)  | (     | (     | 4)    |
|           |       | 30)** | 28)** |       | 16)** | 11)** |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| FSSE      | 33    | 58    | 78    | 97    | **65  | **85  | **315 |
|           | (32)  | (30)  | (25)  | (15)  | (     | (     | (     |
|           |       |       |       |       | 6)**  | 2)**  | 2)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | 29    | 53    | 75    | 94    | 152   | 293   | 544   |
|           | (35)  | (33)  | (31)  | (29)  | (25)  | (21)  | (17)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 42    | 75    | 107   | 138   | 202   | 236   | 310   |
| Official  |       |       |       |       |       |       |       |
|           | \(3   | \(3   | \(2   | \(2   | \(2   | \(    | \(    |
| (         | 400\) | 116\) | 848\) | 575\) | 117\) | 649\) | 535\) |
| 1995-2004 |       |       |       |       |       |       |       |
| mean)     |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

![](media/image1.pct){width="6.498611111111111in"
height="5.000694444444444in"}

Figure 1. Best track positions for Hurricane Epsilon, 29 November - 8
December 2005.

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

Figure 2. Selected wind observations and best track maximum sustained
surface wind speed curve for Hurricane Epsilon, 29 November - 8 December
2005.

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

Figure 3. Selected pressure observations and best track minimum central
pressure curve for Hurricane Epsilon, 29 November - 8 December 2005.

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