Number range CHAPTERTropical Cyclone Report

Hurricane Hilary

19-25 August 2005

James L. Franklin

National Hurricane Center

1 February 2006

Hurricane Hilary was a category 2 hurricane (on the Saffir-Simpson
Hurricane Scale) that brought tropical storm force winds to the Mexican
coast near Manzanillo.

a.  Synoptic History

    The tropical wave associated with the genesis of Hilary moved across
    the west coast of Africa on 4 August. At that time the wave was
    associated with a large amount of deep convection, but the
    convection quickly diminished over the eastern tropical Atlantic.
    The wave moved westward without development, crossing northern South
    America and entering the eastern North Pacific on 17 August. By the
    following day a well-defined mid-level circulation had developed
    within the wave along with some banded convection south of
    Guatemala. The convective organization continued to increase, but
    the system was slow to develop a well-defined surface center of
    circulation. It is estimated that the system finally did so near
    1800 UTC 19 August, becoming a tropical depression about 140 n mi
    south of Puerto Angel, 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. Embedded within a deep easterly current to the south of the
    subtropical ridge, the depression initially moved westward at near
    15 kt and strengthened briskly, becoming a tropical storm by 0600
    UTC 20 August about 190 n mi south of Acapulco, Mexico, and a
    hurricane 18 h later when it was about 290 n mi south of Manzanillo.
    A weakness in the subtropical ridge caused the forward motion to
    slow and Hilary turned toward the northwest on 21 August. The pace
    of intensification also briefly relaxed during this time, but late
    that day Hilary turned back to the west-northwest at a faster
    forward speed and strengthened again, reaching its peak intensity of
    90 kt near 0000 UTC 22 August. This strengthening was accompanied by
    an expansion of the wind field that briefly brought minimal tropical
    storm force winds to the Mexican coast in the Manzanillo area late
    on 21 August.

    On 22 August, Hilary's motion slowed abruptly and the hurricane's
    deep convection began to diminish, particularly in the northern
    semicircle which was over cooler waters. Moving slowly to the
    west-northwest and northwest, Hilary gradually weakened over the
    next couple of days, becoming a tropical storm by 1800 UTC 24 August
    when it was about 435 n mi west of Cabo San Lucas, Mexico, and a
    tropical depression 24 h later. The system had lost the requisite
    convection of a tropical cyclone by 0000 UTC 26 August. Hilary's
    remnant low moved generally westward before dissipating early on 28
    August about 1075 n mi west-northwest of Cabo San Lucas.

b.  Meteorological Statistics

    Observations in Hilary (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 Hilary.

    Ship reports of winds of tropical storm force associated with Hilary
    are given in Table 2. Manzanillo reported sustained winds of 35 kt,
    with gusts to 40 kt, at 2145 UTC 21 August.

c.  Casualty and Damage Statistics

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

d.  Forecast and Warning Critique

    NHC Tropical Weather Outlooks first indicated the potential for
    tropical cyclone formation from Hilary's precursor disturbance about
    24 h prior to genesis.

    Average official track errors for Hilary were considerably lower
    than the average official track errors for the 10-yr period
    1995-2004 (Table 3). Among the dynamical models, the GFS (and in
    particular the GFS ensemble mean, AEMI) and the GFDL performed well
    with Hilary. The consensus models also did well.

    Average official intensity errors were 6, 8, 8, 10, 14, 17, and 19
    kt for the 12, 24, 36, 48, 72, 96, and 120 h forecasts,
    respectively, and were generally less than the average long-term
    official intensity errors (6, 11, 14, 17, 19, 18, and 19 kt,
    respectively).

    Warnings associated with Hilary are given in Table 4. The tropical
    storm warning was issued only after the onset of tropical storm
    force winds at the coastline, as the increase in the size of
    Hilary's wind field was not anticipated. Forecasting the wind
    structure of tropical cyclones, particularly in the vicinity of
    complex terrain, continues to pose significant challenges.
    Interestingly, there were indications in the GFS model fields that
    the wind field would expand.

Number range CHAPTERTable 1. Best track for Hurricane Hilary, 19-25
August 2005.

+--------+--------+--------+---------+---------+---------------------+
| Dat    | La     | Lon    | P       | Wind    | Stage               |
| e/Time | titude | gitude | ressure | Speed   |                     |
|        |        |        |         |         |                     |
| (UTC)  | (°N)   | (°W)   | (mb)    | (kt)    |                     |
+--------+--------+--------+---------+---------+---------------------+
| 19 /   | 13.3   | 96.6   | 1007    | 25      | tropical depression |
| 1800   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 20 /   | 13.5   | 98.2   | 1006    | 30      | \"                  |
| 0000   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 20 /   | 13.6   | 99.8   | 1002    | 40      | tropical storm      |
| 0600   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 20 /   | 13.8   | 101.3  | 997     | 50      | \"                  |
| 1200   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 20 /   | 14.0   | 102.5  | 994     | 55      | \"                  |
| 1800   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 21 /   | 14.3   | 103.7  | 987     | 65      | hurricane           |
| 0000   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 21 /   | 14.9   | 104.7  | 983     | 70      | \"                  |
| 0600   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 21 /   | 15.7   | 105.6  | 981     | 70      | \"                  |
| 1200   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 21 /   | 16.5   | 107.1  | 979     | 75      | \"                  |
| 1800   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 22 /   | 17.2   | 108.5  | 972     | 90      | \"                  |
| 0000   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 22 /   | 17.8   | 110.0  | 970     | 90      | \"                  |
| 0600   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 22 /   | 18.3   | 111.5  | 972     | 90      | \"                  |
| 1200   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 22 /   | 18.6   | 112.3  | 974     | 85      | \"                  |
| 1800   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 23 /   | 18.9   | 113.2  | 976     | 80      | \"                  |
| 0000   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 23 /   | 19.2   | 114.1  | 981     | 75      | \"                  |
| 0600   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 23 /   | 19.6   | 114.9  | 983     | 70      | \"                  |
| 1200   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 23 /   | 20.0   | 115.6  | 985     | 70      | \"                  |
| 1800   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 24 /   | 20.4   | 116.1  | 986     | 65      | \"                  |
| 0000   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 24 /   | 20.9   | 116.7  | 987     | 65      | \"                  |
| 0600   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 24 /   | 21.4   | 117.2  | 990     | 65      | \"                  |
| 1200   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 24 /   | 22.0   | 117.7  | 994     | 55      | tropical storm      |
| 1800   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 25 /   | 22.7   | 118.4  | 998     | 45      | \"                  |
| 0000   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 25 /   | 23.3   | 119.1  | 1000    | 40      | \"                  |
| 0600   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 25 /   | 23.9   | 119.9  | 1002    | 35      | \"                  |
| 1200   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 25 /   | 24.3   | 120.7  | 1003    | 30      | tropical depression |
| 1800   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 26 /   | 24.7   | 121.6  | 1004    | 25      | low                 |
| 0000   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 26 /   | 25.0   | 122.6  | 1005    | 25      | \"                  |
| 0600   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 26 /   | 25.3   | 123.6  | 1006    | 25      | \"                  |
| 1200   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 26 /   | 25.6   | 124.6  | 1007    | 25      | \"                  |
| 1800   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 27 /   | 25.7   | 125.5  | 1008    | 25      | \"                  |
| 0000   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 27 /   | 25.7   | 126.5  | 1008    | 25      | \"                  |
| 0600   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 27 /   | 25.6   | 127.5  | 1009    | 25      | \"                  |
| 1200   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 27 /   | 25.5   | 128.5  | 1009    | 25      | \"                  |
| 1800   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 28 /   | 25.5   | 129.4  | 1010    | 25      | \"                  |
| 0000   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 28 /   |        |        |         |         | dissipated          |
| 0600   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+
| 22 /   | 17.8   | 110.0  | 970     | 90      | minimum pressure    |
| 0600   |        |        |         |         |                     |
+--------+--------+--------+---------+---------+---------------------+

Number range CHAPTERTable 2. Selected ship reports with winds of at
least 34 kt for Hurricane Hilary, 19-25 August 2005.

+-----------+-----------+-----------+-----------+-----------+-----------+
| Date/Time | Ship call | Latitude  | Longitude | Wind      | Pressure  |
| (UTC)     | sign      |           |           |           |           |
|           |           | (°N)      | (°W)      | dir/speed | (mb)      |
|           |           |           |           | (kt)      |           |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 20 / 0000 | PBBR      | 10.3      | 104.7     | 290 / 35  | 1008.2    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 21 / 2100 | DGVC      | 18.6      | 103.9     | 130 / 45  | 1008.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 21 / 2100 | WCZ523    | 19.3      | 105.6     | 120 / 37  | 1006.1    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 22 / 0000 | WCZ523    | 19.2      | 105.2     | 160 / 40  | 1008.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 22 / 0000 | 3FZP8     | 20.0      | 106.5     | 140 / 37  | 1005.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 22 / 0600 | JKHH      | 20.3      | 107.9     | 110 / 36  | 1009.2    |
+-----------+-----------+-----------+-----------+-----------+-----------+

Number range CHAPTERTable 3. Preliminary forecast evaluation
(heterogeneous sample) for Hurricane Hilary, 19-25 August 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.

+-----------+-------+-------+-------+-------+-------+-------+-------+
| Number    | For   |       |       |       |       |       |       |
| range     | ecast |       |       |       |       |       |       |
| CHAPTE    | P     |       |       |       |       |       |       |
| RForecast | eriod |       |       |       |       |       |       |
| Technique | (h)   |       |       |       |       |       |       |
+===========+=======+=======+=======+=======+=======+=======+=======+
|           | 12    | 24    | 36    | 48    | 72    | 96    | 120   |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CLP5      | 40    | 76    | 99    | 122   | 158   | 186 ( | 222 ( |
|           | (23)  | (21)  | (19)  | (17)  | (13)  | 9)    | 5)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFNI      | 51    | 91    | 122   | 154   | 215   | 218 ( | 299 ( |
|           | (22)  | (20)  | (18)  | (16)  | (12)  | 7)    | 3)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDI      | **32  | **45  | **43  | **48  | 101   | 153 ( | 182 ( |
|           | (     | (     | (     | (     | (13)  | 9)    | 5)    |
|           | 23)** | 21)** | 19)** | 17)** |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFSI      | 39    | **53  | **60  | **68  | 107 ( | 135 ( | **114 |
|           | (21)  | (     | (     | (     | 9)    | 5)    | (     |
|           |       | 17)** | 15)** | 13)** |       |       | 1)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| AEMI      | **34  | **56  | **61  | **63  | **84  | **91  | **119 |
|           | (     | (     | (     | (     | (     | (     | (     |
|           | 23)** | 21)** | 19)** | 17)** | 13)** | 9)**  | 5)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NGPI      | 47    | 84    | 110   | 138   | 188   | 267 ( | 552 ( |
|           | (22)  | (20)  | (18)  | (16)  | (12)  | 8)    | 4)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| UKMI      | 40    | 70    | 91    | 103   | 136   | 157 ( | 157 ( |
|           | (23)  | (21)  | (19)  | (17)  | (13)  | 9)    | 5)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMD      | 38    | 68    | 86    | 109   | 163   | 215 ( | 209 ( |
|           | (23)  | (21)  | (19)  | (17)  | (13)  | 9)    | 5)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMM      | **35  | 68    | 99    | 138   | 202   | 188 ( | 186 ( |
|           | (     | (21)  | (19)  | (17)  | (13)  | 9)    | 5)    |
|           | 23)** |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMS      | 37    | 65    | 90    | 123   | 168   | 148 ( | 178 ( |
|           | (23)  | (21)  | (19)  | (17)  | (13)  | 9)    | 5)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CONU      | **33  | **56  | 72    | 85    | 118   | 134 ( | 222 ( |
|           | (     | (     | (19)  | (17)  | (13)  | 9)    | 5)    |
|           | 23)** | 21)** |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GUNA      | **33  | **53  | **62  | **69  | 110 ( | 131 ( | 178 ( |
|           | (     | (     | (     | (     | 9)    | 5)    | 1)    |
|           | 20)** | 17)** | 15)** | 13)** |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| FSSE      | **32  | **51  | **60  | **67  | **90  | 130 ( | 142 ( |
|           | (     | (     | (     | (     | (     | 6)    | 2)    |
|           | 20)** | 18)** | 16)** | 14)** | 10)** |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | 37    | 59    | 70    | 73    | 94    | 115 ( | 120 ( |
|           | (23)  | (21)  | (19)  | (17)  | (13)  | 9)    | 5)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 37    | 68    | 97    | 123   | 175   | 208   | 259   |
| Official  | (     | (     | (     | (     | (     | (355) | (224) |
|           | 2654) | 2378) | 2096) | 1829) | 1386) |       |       |
| (         |       |       |       |       |       |       |       |
| 1995-2004 |       |       |       |       |       |       |       |
| mean)     |       |       |       |       |       |       |       |
| [^1]      |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

Number range CHAPTERTable 4. Watch and warning summary for Hurricane
Hilary, 19-25 August 2005.

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

  21 / 2200               Tropical Storm Warning  Punta San Telmo to Cabo
                          issued                  Corrientes

  22 / 0900               Tropical Storm Warning  Punta San Telmo to Cabo
                          discontinued            Corrientes
  ----------------------- ----------------------- -----------------------

![](media/image1.wmf){width="7.372916666666667in"
height="5.771527777777778in"}

Number range CHAPTERFigure 1. Best track positions for Hurricane Hilary,
19-25 August 2005.

![](media/image2.wmf){width="6.930555555555555in"
height="4.819444444444445in"}

Number range CHAPTERFigure 2. Selected wind observations and best track
maximum sustained surface wind speed curve for Hurricane Hilary, 19-25
August 2005.

![](media/image3.wmf){width="6.930555555555555in"
height="4.819444444444445in"}

Number range CHAPTERFigure 3. Selected pressure observations and best
track minimum central pressure curve for Hurricane Hilary, 19-25 August
2005.

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