Number range CHAPTERTropical Cyclone Report

Hurricane Philippe

17-23 September 2005

James L. Franklin

National Hurricane Center

9 February 2006

Hurricane Philippe was a category 1 hurricane (on the Saffir-Simpson
Hurricane Scale) that is notable for a drawn-out dissipation within the
circulation of a large non-tropical low.

a.  Synoptic History

    Philippe appears to have developed from a tropical wave that moved
    across the west coast of Africa on 9 September. The wave quickly
    lost nearly all of its convection as it moved westward and became
    difficult to track, but on 13 September an area of showers
    re-developed about 1200 n mi east of the southern Windward Islands.
    Maintaining convection over a large area, the sprawling disturbance
    continued westward without significant development until 16
    September, when convection became more concentrated in the southern
    part of the disturbance about 650 n mi east of Trinidad. QuikSCAT
    ambiguity data from 0924 UTC 17 September indicate that the system's
    circulation was becoming better defined, and it is estimated that a
    tropical depression formed near 1200 UTC that day about 300 n mi
    east of Barbados.

    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. Steering currents were unusually weak for a system so far
    south in the tropical Atlantic at the height of the hurricane
    season, and the depression moved slowly northwestward initially as
    it strengthened, becoming a tropical storm at 1800 UTC 17 September.
    Philippe moved generally to the north-northwest over the next couple
    of days towards a weakness in the subtropical ridge, becoming a
    hurricane at 0000 UTC 19 September about 315 n mi east of the
    northern Leeward Islands, and reaching its peak intensity of 70 kt
    about 24 h later.

    While Philippe was strengthening to the east of the Lesser Antilles,
    Tropical Storm Rita had formed in the Bahamas. Rita generated an
    impressive outflow pattern on 19 September, and the aforementioned
    downstream weakness in the subtropical ridge amplified into a large
    mid- to upper-level cold low to the north of the Lesser Antilles the
    following day. Westerly shear on the south side of the cold low
    began to impact Philippe, which weakened to a tropical storm by 1200
    UTC 20 September. By late in the day, Philippe's low-level center
    had become exposed to the west of the diminishing convection. While
    Philippe was weakening on 21 September, it turned northward and
    accelerated along the east side of the strengthening cold low, which
    was developing its own surface reflection. During the day on 22
    September, Philippe was little more than a swirl of low clouds
    generating only intermittent convection, and in fact may have
    temporarily lost its closed surface circulation within the broader
    cyclonic envelope of the cold low (Figure 4). Late in the day,
    however, Philippe moved north-northwestward into the large curved
    band of shallow convection associated with the cold low, and as it
    did so deep convection re-developed near the center of the tropical
    cyclone. Looping around the larger low, Philippe turned
    northwestward and then accelerated westward overnight. By 1200 UTC
    23 September, deep convection associated with the tropical cyclone
    was diminishing again, and Philippe weakened to a tropical
    depression. The cyclone degenerated to a remnant low by 1800 UTC.
    The remnant circulation continued to loop cyclonically, losing its
    closed circulation after 0600 UTC the following day, although the
    remnant vorticity center could be followed for another day or so.

b.  Meteorological Statistics

    Observations in Philippe (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), as well as flight-level
    and dropwindsonde observations from flights of the 53^rd^ Weather
    Reconnaissance Squadron of the U. S. Air Force Reserve Command.
    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 the cyclone.

    The estimated peak intensity of Philippe, 70 kt at 0000 UTC 20
    September, is lower than the satellite Dvorak estimates (Figs. 2,
    3); the 90-kt classifications were based on the embedded center
    pattern -- perhaps the least reliable pattern of the technique. The
    rapid decay of the satellite appearance the following day suggests
    that Philippe may not have been as strong as these classifications
    indicated.

    Ship C6SE5 reported winds of 49 kt at 1800 UTC 17 September when it
    was about 90 n mi north of the cyclone center. This report has been
    discounted, since it is at odds with nearby buoy reports as well as
    with data from a reconnaissance aircraft investigating Philippe at
    that time. No other ship reports of tropical storm force winds were
    associated with the circulation of Philippe. Other observations of
    note include visually-estimated surface winds of near 40 kt in the
    southeastern quadrant during the first investigative flight into the
    cyclone on 17 September, and a peak 850 mb reconnaissance
    flight-level wind of 83 kt at 0028 UTC 19 September.

c.  Casualty and Damage Statistics

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

d.  Forecast and Warning Critique

    The genesis of Philippe was well-anticipated in Tropical Weather
    Outlooks, which first mentioned the possibility of tropical cyclone
    formation three days prior to genesis.

    A verification of official and guidance model track forecasts is
    given in Table 2. Average official track errors for Philippe were
    50, 86, 118, 134, 160, 234, and 302 n mi for the 12, 24, 36, 48, 72,
    96, and 120 h forecasts, respectively. The number of forecasts
    ranged from 23 at 12 h to only 5 at 120 h. Despite a very
    complicated synoptic environment, these errors are by and large
    comparable to the long-term average official track errors (Table 2).
    Some of the primary track guidance models, including the GFDI and
    GFSI, outperformed the official forecast, as did the consensus
    models. The official forecasts did not anticipate the looping motion
    resulting from Philippe's interaction with the large non-tropical
    low (whose development was not handled well by the global models).
    Consequently, early forecasts had a fairly substantial westward
    bias, while later forecasts assumed Philippe would remain a
    vertically-coherent system and incorrectly took Philippe
    northeastward into the mid-latitudes. Many of these forecasts of
    recurvature were unverifiable due to the dissipation of the system.

    Average official intensity errors were 7, 12, 19, 26, 40, 52, and 62
    kt for the 12, 24, 36, 48, 72, 96, and 120 h forecasts,
    respectively. These errors, particularly at the later times, are far
    larger than the long-term mean errors (6, 10, 12, 15, 18, 20, and 22
    kt, respectively), and resulted from a failure to anticipate the
    shearing effects of the developing cold low. The GFDL, whose model
    storms are often impervious to shear, strongly overdeveloped
    Philippe. The official forecasts were more conservative but still
    too aggressive.

Warnings associated with Philippe are listed in Table 3. The tropical
storm warning for Bermuda proved to be unnecessary. No watches or
warnings were issued for the Lesser Antilles, even though the system
developed about 300 n mi east of Barbados and climatology indicated an
impact in the islands. The official forecasts correctly anticipated that
Philippe would pass safely to the east.

Number range CHAPTERTable 1. Best track for Hurricane Philippe, 17-23
September 2005.

+--------+---------+--------+--------+---------+---------------------+
| Dat    | L       | Lon    | Pr     | Wind    | Stage               |
| e/Time | atitude | gitude | essure | Speed   |                     |
|        |         |        |        |         |                     |
| (UTC)  | (°N)    | (°W)   | (mb)   | (kt)    |                     |
+--------+---------+--------+--------+---------+---------------------+
| 17 /   | 13.3    | 54.5   | 1008   | 30      | tropical depression |
| 1200   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 17 /   | 13.5    | 54.9   | 1007   | 35      | tropical storm      |
| 1800   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 18 /   | 13.9    | 55.1   | 1003   | 40      | \"                  |
| 0000   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 18 /   | 14.4    | 55.3   | 1000   | 45      | \"                  |
| 0600   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 18 /   | 14.9    | 55.5   | 996    | 50      | \"                  |
| 1200   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 18 /   | 15.6    | 55.7   | 993    | 55      | \"                  |
| 1800   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 19 /   | 16.2    | 55.8   | 987    | 65      | hurricane           |
| 0000   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 19 /   | 16.7    | 55.9   | 987    | 65      | \"                  |
| 0600   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 19 /   | 17.2    | 56.2   | 987    | 65      | \"                  |
| 1200   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 19 /   | 17.5    | 56.4   | 987    | 65      | \"                  |
| 1800   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 20 /   | 17.7    | 56.6   | 985    | 70      | \"                  |
| 0000   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 20 /   | 17.9    | 56.8   | 987    | 65      | \"                  |
| 0600   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 20 /   | 18.1    | 57.0   | 990    | 60      | tropical storm      |
| 1200   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 20 /   | 18.5    | 57.2   | 992    | 55      | \"                  |
| 1800   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 21 /   | 18.9    | 57.2   | 994    | 55      | \"                  |
| 0000   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 21 /   | 19.4    | 57.1   | 997    | 50      | \"                  |
| 0600   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 21 /   | 19.9    | 57.0   | 1000   | 45      | \"                  |
| 1200   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 21 /   | 20.8    | 56.9   | 1001   | 40      | \"                  |
| 1800   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 22 /   | 22.4    | 56.7   | 1002   | 35      | \"                  |
| 0000   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 22 /   | 23.8    | 56.8   | 1003   | 35      | \"                  |
| 0600   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 22 /   | 25.2    | 57.2   | 1003   | 35      | \"                  |
| 1200   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 22 /   | 26.7    | 57.6   | 1003   | 35      | \"                  |
| 1800   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 23 /   | 28.3    | 58.2   | 1003   | 35      | \"                  |
| 0000   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 23 /   | 30.2    | 60.1   | 1003   | 35      | \"                  |
| 0600   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 23 /   | 30.5    | 62.2   | 1003   | 30      | tropical depression |
| 1200   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 23 /   | 30.2    | 63.7   | 1003   | 30      | remnant low         |
| 1800   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 24 /   | 29.2    | 63.8   | 1003   | 30      | \"                  |
| 0000   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 24 /   | 28.6    | 62.8   | 1004   | 25      | \"                  |
| 0600   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+
| 24 /   |         |        |        |         | absorbed within     |
| 1200   |         |        |        |         | non-tropical low    |
+--------+---------+--------+--------+---------+---------------------+
| 20 /   | 17.7    | 56.6   | 985    | 70      | minimum pressure    |
| 0000   |         |        |        |         |                     |
+--------+---------+--------+--------+---------+---------------------+

Number range CHAPTERNumber range CHAPTERNumber range CHAPTERTable 2.
Preliminary forecast evaluation (heterogeneous sample) for Hurricane
Philippe, 17-23 September 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.

+-----------+-------+-------+-------+-------+-------+-------+-------+
| Number    | For   |       |       |       |       |       |       |
| range     | ecast |       |       |       |       |       |       |
| CHAPTE    | P     |       |       |       |       |       |       |
| RForecast | eriod |       |       |       |       |       |       |
| Technique | (h)   |       |       |       |       |       |       |
+===========+=======+=======+=======+=======+=======+=======+=======+
|           | 12    | 24    | 36    | 48    | 72    | 96    | 120   |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CLP5      | 69    | 130   | 180   | 215   | 215   | 284 ( | 447 ( |
|           | (23)  | (21)  | (19)  | (17)  | (13)  | 9)    | 5)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFNI      | 56    | 100   | 123   | 149   | 175   | **133 | **138 |
|           | (21)  | (18)  | (17)  | (15)  | (11)  | (     | (     |
|           |       |       |       |       |       | 7)**  | 3)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDI      | **41  | **66  | **82  | **93  | **109 | **207 | **203 |
|           | (     | (     | (     | (     | (     | (     | (     |
|           | 23)** | 21)** | 19)** | 17)** | 13)** | 9)**  | 5)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFSI      | **48  | **71  | **89  | **107 | **136 | 247 ( | 324 ( |
|           | (     | (     | (     | (     | (     | 8)    | 4)    |
|           | 22)** | 20)** | 18)** | 16)** | 12)** |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| AEMI      | 56    | 93    | 121   | 145   | 185   | 306 ( | 333 ( |
|           | (22)  | (20)  | (18)  | (16)  | (12)  | 8)    | 4)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NGPI      | 56    | 97    | 141   | 174   | 221   | **233 | **236 |
|           | (23)  | (21)  | (19)  | (17)  | (13)  | (     | (     |
|           |       |       |       |       |       | 7)**  | 3)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| UKMI      | 56    | 101   | 148   | 164   | 187   | **219 | **205 |
|           | (22)  | (20)  | (18)  | (16)  | (12)  | (     | (     |
|           |       |       |       |       |       | 8)**  | 4)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| A98E      | 61    | 102   | 131   | **125 | **151 | 245 ( | **248 |
|           | (23)  | (21)  | (19)  | (     | (     | 9)    | (     |
|           |       |       |       | 17)** | 13)** |       | 5)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| A9UK      | 59    | 104   | 128   | 136 ( | 218 ( |       |       |
|           | (12)  | (11)  | (10)  | 9)    | 7)    |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMD      | 53    | **85  | **109 | **116 | **116 | **155 | **273 |
|           | (23)  | (     | (     | (     | (     | (     | (     |
|           |       | 21)** | 19)** | 17)** | 13)** | 9)**  | 5)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMM      | 59    | 96    | 125   | 143   | 174   | 253 ( | 349 ( |
|           | (23)  | (21)  | (19)  | (17)  | (13)  | 9)    | 5)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMS      | 71    | 123   | 168   | 203   | 273   | 384 ( | 439 ( |
|           | (22)  | (21)  | (19)  | (17)  | (13)  | 9)    | 5)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CONU      | **43  | **75  | **102 | **119 | **145 | **173 | **203 |
|           | (     | (     | (     | (     | (     | (     | (     |
|           | 23)** | 21)** | 19)** | 17)** | 13)** | 8)**  | 4)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GUNA      | **45  | **76  | **108 | **125 | **147 | **192 | **224 |
|           | (     | (     | (     | (     | (     | (     | (     |
|           | 22)** | 20)** | 18)** | 16)** | 12)** | 7)**  | 3)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| FSSE      | **45  | **75  | **97  | **105 | **148 | 239 ( | 312 ( |
|           | (     | (     | (     | (     | (     | 7)    | 3)    |
|           | 21)** | 19)** | 17)** | 15)** | 11)** |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | 50    | 86    | 118   | 134   | 160   | 234 ( | 302 ( |
|           | (23)  | (21)  | (19)  | (17)  | (13)  | 9)    | 5)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 42    | 75    | 107   | 138   | 202   | 236   | 310   |
| Official  | (     | (     | (     | (     | (     | (649) | (535) |
|           | 3400) | 3116) | 2848) | 2575) | 2117) |       |       |
| (         |       |       |       |       |       |       |       |
| 1995-2004 |       |       |       |       |       |       |       |
| mean[^1]) |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

Number range CHAPTERTable 4. Watch and warning summary for Hurricane
Philippe, 17-23 September 2005.

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

  23 / 1300               Tropical Storm Warning  Bermuda
                          issued                  

  23 / 2100               Tropical Storm Warning  Bermuda
                          discontinued            
  ----------------------- ----------------------- -----------------------

![](media/image1.wmf){width="8.001388888888888in"
height="6.156944444444444in"}

Number range CHAPTERFigure 1. Best track positions for Hurricane
Philippe, 17-23 September 2005.

![](media/image2.wmf){width="7.997916666666667in"
height="5.440972222222222in"}

Number range CHAPTERFigure 2. Selected wind observations and best track
maximum sustained surface wind speed curve for Hurricane Philippe, 17-23
September 2005. Aircraft observations have been adjusted for elevation
using 90%, 80%, and 80% reduction factors for observations from 700 mb,
850 mb, and 1500 ft, respectively.

![](media/image3.wmf){width="7.997916666666667in"
height="5.436111111111111in"}

Number range CHAPTERFigure 3. Selected pressure observations and best
track minimum central pressure curve for Hurricane Philippe, 17-23
September 2005.

![](media/image4.png){width="7.879861111111111in"
height="5.909722222222222in"}

Number range CHAPTERFigure 4. GOES-12 visible image at 1245 UTC 22
September 2005, showing the circulation of Philippe

> (centered near 25°N, 57°W within the dashed orange circle) embedded
> within a larger non-tropical low.

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