Number range CHAPTERTropical Cyclone Report

Hurricane Gordon

(AL072006)

10-20 September 2006

Eric S. Blake

National Hurricane Center

14 November 2006

Gordon was a category 3 hurricane (on the Saffir-Simpson Hurricane
Scale) that affected the Azores as a hurricane, causing minimal damage.
As an extratropical system it brought heavy rains and high winds to
parts of western Europe, causing substantial power outages and at least
five injuries.

a.  Synoptic History

Gordon formed from a tropical wave that left the west coast of Africa on
1 September. This wave was initially well-organized with an associated
low along the wave axis and some convection. However, vertical wind
shear from an upper-level trough east of tropical storm Florence
hindered any development. This synoptic situation remained nearly the
same for about a week, as the wave progressed westward without
significant organization. By 9 September, the upper trough associated
with Florence had moved far enough away from the wave to cause a
decrease in shear. Convection increased around the low overnight and, at
1800 UTC 10 September, it is estimated that a tropical depression
formed, centered about 470 n mi east-northeast of the Leeward Islands.
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.

Initially, moderate shear from the upper trough allowed for only a
modest intensification of the depression, and the system became a
tropical storm on 11 September at 1200 UTC. Gordon continued moving
toward the west-northwest, then slowed as it turned toward the northwest
on 12 September, heading into a weakness in the subtropical ridge left
behind Florence. The upper trough that had been hindering Gordon's
development weakened and moved to the southwest, causing shear to abate
over the tropical cyclone. The storm turned toward the north and
intensified into a hurricane, forming a large ragged eye early on 13
September. Gordon then rapidly intensified, with convection in the
eyewall deepening and the eye becoming better-defined. The cyclone
strengthened 50 kt in the 30 h period from 1800 UTC 12 September until
0000 UTC 14 September, when it reached a peak intensity of 105 kt while
centered about 500 n mi east-southeast of Bermuda. It maintained its
peak intensity for about 24 h, during which time the eye of the
hurricane shrunk a little but the cloud tops in the eyewall warmed a
bit.

Gordon turned toward the northeast and accelerated somewhat on 14
September, but an upper trough that had been steering the system
bypassed the hurricane late that day. As a result, middle-tropospheric
ridging rebuilt to the north of the tropical cyclone and Gordon's motion
ground to a halt by midday on 15 September, about 575 n mi
east-southeast of Bermuda. Vertical wind shear increased somewhat and
the cyclone weakened, barely maintaining hurricane-strength on 16
September as it drifted northwestward. The leisurely motion during this
time also caused increased upwelling of cooler water beneath the
hurricane, contributing to a weakening of the deep convection associated
with the tropical cyclone. Early on 17 September, a building high to the
east of Gordon finally restarted the hurricane's motion to the northeast
at about 5 to 10 kt.

Gordon acccelerated to the northeast on 18 September, and turned to the
east-northeast later that day around the strengthening subtropical high.
Vertical wind shear relaxed during this time and convection redeveloped
around the eye. The cyclone reached a second peak intensity of 90 kt on
19 September at 0600 UTC about 420 n mi west-southwest of the Azores,
despite the storm moving over relatively cool waters of about 25°C.
Below normal upper-tropospheric temperatures in the subtropical Atlantic
Ocean were at least partially responsible for allowing the hurricane to
get stronger than typically occurring over cool waters. Gordon was
moving quickly eastward between 25 and 30 kt at this time between a
large trough over the North Atlantic Ocean and the subtropical ridge.
The tropical cyclone finally started weakening later on 19 September as
a combination of lower sea-surface temperatures and increasing wind
shear took its toll. The hurricane moved a little south of due east
overnight on 20 September, allowing its radius of maximum winds to stay
south of the Azores. Gordon's center went between the islands of São
Miguel and Santa Maria in the Azores at about 0900 UTC 20 September,
bringing hurricane-force wind gusts to Santa Maria. Later that day,
Gordon began interacting with a cold front and weakened, and the system
became extratropical at 0000 UTC 21 September about 240 n mi west of the
west coast of Portugal.

The extratropical phase of Gordon was rather eventful as it retained the
majority of its strength from its tropical phase, maintaining winds of
55 kt or greater for almost two days after transitioning from a tropical
cyclone. Gordon continued moving quickly to the northeast and was driven
northward at almost 50 kt on 21 September around a larger
middle-latitude extratropical low that captured the storm. Gordon
remained distinct from the larger system, and brought heavy rain and
high winds to Spain, England and Ireland, with winds gusts of
hurricane-force recorded. An interaction with the middle-latitude system
produced another deepening period and QuikSCAT indicated that Gordon's
extratropical remnant briefly regained sustained winds of
hurricane-force early on 22 September. Surface analyses show that the
post-Gordon cyclone became the dominant low pressure area and made a
large cyclonic loop while slowly weakening over the far northeastern
Atlantic Ocean. The system completed the loop just south of Ireland on
24 September and the low dissipated between Ireland and England later
that day.

b.  Meteorological Statistics

    Observations in Gordon (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
    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 Gordon. The peak intensity of 105 kt in Gordon is based
    on objective Dvorak T-numbers, which suggested the storm was a
    little stronger than subjective T-numbers alone would imply. Figure
    4 shows Gordon as it was rapidly intensifying a few hours before
    reaching its peak intensity.

    Ship reports of winds of tropical storm force associated with Gordon
    are given in Table 2, and selected surface observations from land
    stations and data buoys are given in Table 3. A peak wind gust of 71
    kt was recorded in the Azores as Gordon passed. During the
    extratropical portion of Gordon, a wind gust of 99 kt was recorded
    on the northwest coast of Spain at an elevated location. The British
    Broadcasting Corporation (BBC) reported that wind gusts to 70 kt
    were measured in southwestern England, but no exact location was
    given.

c.  Casualty and Damage Statistics

    There were no reports of casualties associated with Gordon as a
    tropical cyclone. The BBC reported only minor damage in the Azores,
    consisting of mostly fallen trees and power outages. However, after
    Gordon became an extratropical low, four injuries due to falling
    debris from high wind were reported in Spain. Power was also
    reported out for 100,000 customers after the storm in Spain. The
    strong extratropical Gordon brought high winds and rain that
    affected practice rounds at the Ryder Cup golf tournament in
    Ireland. About 126,000 homes were without power after the storm in
    Northern Ireland and one injury was reported. No monetary damage
    figures are available.

d.  Forecast and Warning Critique

    The timing of the genesis of Gordon was not particularly
    well-anticipated, although the system that eventually became Gordon
    was mentioned in the Tropical Weather Outlook products for 5 days
    prior to genesis. It was initially thought that the system could
    become a tropical depression in the eastern Atlantic Ocean, but a
    depression did not form. On 10 September, the possibility that the
    wave that eventually became Gordon could become a depression was
    only mentioned about six hours before the first advisory was issued.

    A verification of official and guidance model track forecasts is
    given in Table 4. Average official track errors for Gordon were 28,
    54, 86, 129, 227, 332, and 361 n mi for the 12, 24, 36, 48, 72, 96,
    and 120 h forecasts, respectively. The number of forecasts ranged
    from 38 at 12 h to 19 at 120 h. These errors are comparable to the
    average long-term official track errors (Table 4) through about 36
    hours, and are larger than the long-term averages from 48-120 h.
    Perhaps it is not surprising that the track errors were large, in
    view of the fact that CLP5 errors were also unusually large. There
    were some good individual model performances. The GFDI model had low
    errors until 48 h, while the NGPI had a good performance beyond
    48 h. The UKMI struggled with this system, having an average error
    of 611 n mi at 5 days.

    Average official intensity errors were 7, 11, 15, 17, 23, 21, and 21
    kt for the 12, 24, 36, 48, 72, 96, and 120 h forecasts,
    respectively. For comparison, the average long-term official
    intensity errors are 6, 10, 12, 14, 18, 20, and 22 kt, respectively.
    The official forecast errors were generally a little worse than
    average for Gordon (Table 5). There was also a substantial low bias
    in the official forecast for Gordon, especially at 48 h and beyond
    where the bias was 17 kt or greater. The re-intensification of
    Gordon at higher-latitudes was not anticipated and this contributed
    to the low bias. The SHIPS model also had a similar intensity bias.
    On the other hand, the GFDI model had extremely low errors and
    biases. In fact, at 96 and 120 h, the errors of the GFDI were about
    half that of the official forecast.

    Table 6 lists the tropical cyclone watches/warnings advisories that
    were issued for Gordon. At first, a tropical storm watch was issued
    for the Azores due to the expectation that the hurricane would
    weaken before reaching the Islands. However the watch was upgraded
    to a hurricane warning 6 h later as the Gordon continued to
    intensify. Tropical storm conditions began affecting the Azores
    about 33 h after the watch was issued and about 27 h after the
    hurricane warning was issued. No sustained hurricane-force winds
    were reported, with QuikSCAT suggesting that these winds stayed just
    south of Santa Maria Island.

Number range CHAPTERTable 1. Best track for Hurricane Gordon, 10-20
September 2006.

+----------+----------+----------+---------+---------+--------------+
| D        | Latitude | L        | P       | Wind    | Stage        |
| ate/Time |          | ongitude | ressure | Speed   |              |
|          | (°N)     |          |         |         |              |
| (UTC)    |          | (°W)     | (mb)    | (kt)    |              |
+----------+----------+----------+---------+---------+--------------+
| 10 /     | 20.2     | 53.8     | 1012    | 25      | tropical     |
| 1800     |          |          |         |         | depression   |
+----------+----------+----------+---------+---------+--------------+
| 11 /     | 20.3     | 54.5     | 1011    | 30      | \"           |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 11 /     | 20.6     | 55.3     | 1010    | 30      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 11 /     | 20.9     | 56.3     | 1008    | 35      | tropical     |
| 1200     |          |          |         |         | storm        |
+----------+----------+----------+---------+---------+--------------+
| 11 /     | 21.4     | 57.1     | 1005    | 40      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 12 /     | 21.8     | 57.6     | 1003    | 50      | \"           |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 12 /     | 22.3     | 58.0     | 1000    | 50      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 12 /     | 22.8     | 58.2     | 998     | 50      | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 12 /     | 23.4     | 58.2     | 994     | 55      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 13 /     | 24.0     | 58.1     | 987     | 65      | hurricane    |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 13 /     | 24.7     | 58.0     | 984     | 70      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 13 /     | 25.6     | 57.9     | 980     | 80      | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 13 /     | 26.5     | 57.7     | 965     | 95      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 14 /     | 27.3     | 57.4     | 955     | 105     | \"           |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 14 /     | 28.2     | 56.8     | 956     | 105     | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 14 /     | 29.1     | 56.2     | 956     | 105     | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 14 /     | 29.8     | 55.4     | 958     | 105     | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 15 /     | 30.3     | 54.6     | 960     | 100     | \"           |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 15 /     | 30.8     | 53.8     | 965     | 95      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 15 /     | 31.1     | 53.5     | 973     | 85      | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 15 /     | 31.1     | 53.5     | 976     | 80      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 16 /     | 31.1     | 53.5     | 980     | 75      | \"           |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 16 /     | 31.2     | 53.6     | 983     | 70      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 16 /     | 31.3     | 53.8     | 987     | 65      | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 16 /     | 31.5     | 53.9     | 987     | 65      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 17 /     | 31.9     | 53.8     | 987     | 65      | \"           |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 17 /     | 32.4     | 53.7     | 987     | 65      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 17 /     | 33.3     | 53.3     | 983     | 70      | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 17 /     | 34.1     | 52.9     | 983     | 70      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 18 /     | 35.0     | 52.1     | 981     | 75      | \"           |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 18 /     | 36.1     | 50.6     | 979     | 75      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 18 /     | 36.9     | 48.7     | 976     | 80      | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 18 /     | 37.5     | 46.3     | 972     | 85      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 19 /     | 38.0     | 43.3     | 972     | 85      | \"           |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 19 /     | 38.1     | 40.2     | 970     | 90      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 19 /     | 38.0     | 37.0     | 977     | 80      | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 19 /     | 37.8     | 33.5     | 979     | 75      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 20 /     | 37.7     | 29.9     | 980     | 70      | \"           |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 20 /     | 37.6     | 26.1     | 980     | 70      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 20 /     | 37.8     | 22.6     | 983     | 65      | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 20 /     | 38.5     | 18.5     | 983     | 65      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 21 /     | 40.1     | 14.0     | 984     | 60      | e            |
| 0000     |          |          |         |         | xtratropical |
+----------+----------+----------+---------+---------+--------------+
| 21 /     | 43.8     | 10.4     | 986     | 55      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 21 /     | 48.5     | 9.0      | 982     | 55      | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 21 /     | 52.5     | 9.5      | 978     | 55      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 22 /     | 54.5     | 10.5     | 975     | 60      | \"           |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 22 /     | 57.0     | 14.0     | 974     | 65      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 22 /     | 56.5     | 18.5     | 976     | 55      | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 22 /     | 56.0     | 19.5     | 980     | 45      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 23 /     | 54.5     | 20.0     | 982     | 45      | \"           |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 23 /     | 52.5     | 20.0     | 986     | 40      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 23 /     | 50.7     | 17.7     | 993     | 35      | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 23 /     | 49.0     | 14.5     | 994     | 35      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 24 /     | 48.0     | 10.0     | 995     | 30      | \"           |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 24 /     | 48.5     | 8.5      | 996     | 30      | \"           |
| 0600     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 24 /     | 49.0     | 8.0      | 998     | 30      | \"           |
| 1200     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 24 /     | 50.5     | 7.5      | 1001    | 25      | \"           |
| 1800     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 25 /     |          |          |         |         | dissipated   |
| 0000     |          |          |         |         |              |
+----------+----------+----------+---------+---------+--------------+
| 14 /     | 27.3     | 57.4     | 955     | 105     | minimum      |
| 0000     |          |          |         |         | pressure     |
+----------+----------+----------+---------+---------+--------------+

Number range CHAPTERTable 2. Selected ship reports with winds of at
least 34 kt for Hurricane Gordon, 10-20 September 2006 .

+-----------+-----------+-----------+-----------+-----------+-----------+
| Date/Time | Ship call | Latitude  | Longitude | Wind      | Pressure  |
| (UTC)     | sign      |           |           |           |           |
|           |           | (°N)      | (°W)      | dir/speed | (mb)      |
|           |           |           |           | (kt)      |           |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 16 / 1600 | DGNB      | 29.7      | 52.1      | 180 / 37  | 1014.4    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 16 / 1700 | DGNB      | 29.6      | 52.4      | 200 / 37  | 1014.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 16 / 1800 | DGNB      | 29.6      | 52.7      | 200 / 37  | 1013.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 16 / 1900 | DGNB      | 29.5      | 53.0      | 210 / 35  | 1012.6    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 20 / 0000 | 4XFV      | 35.4      | 29.4      | 160 / 38  | 1013.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 20 / 0600 | ZCIH7     | 34.7      | 30.4      | 290 / 37  | 1013.1    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 20 / 0600 | DEDM      | 35.6      | 27.5      | 260 / 51  | 1008.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 20 / 1200 | V2RE      | 35.4      | 22.4      | 230 / 41  | 1006.5    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 20 / 1200 | VRZN9     | 35.4      | 21.8      | 210 / 39  | 1008.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 20 / 1800 | V2RE      | 35.9      | 22.0      | 280 / 41  | 1008.5    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 20 / 1800 | A8GX4     | 35.9      | 21.0      | 270 / 41  | 1006.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+

Number range CHAPTERTable 3. Selected surface observations for Hurricane
Gordon, 10-20 September 2006. Selected observations from the
extratropical portion of the cyclone from Spain and England are also
included.

+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Location        | M   |     | M   |       |     | St  | St  | To  |
|                 | ini |     | axi |       |     | orm | orm | tal |
|                 | mum |     | mum |       |     | su  |     |     |
|                 | Sea |     | S   |       |     | rge | t   | r   |
|                 | Le  |     | urf |       |     |     | ide | ain |
|                 | vel |     | ace |       |     | (   |     |     |
|                 | Pr  |     |     |       |     | ft) | (   | (   |
|                 | ess |     | W   |       |     | ^c^ | ft) | in) |
|                 | ure |     | ind |       |     |     | ^d^ |     |
|                 |     |     | Sp  |       |     |     |     |     |
|                 |     |     | eed |       |     |     |     |     |
+=================+=====+=====+=====+=======+=====+=====+=====+=====+
|                 | Da  | Pre | Da  | Sust  | G   |     |     |     |
|                 | te/ | ss. | te/ | ained | ust |     |     |     |
|                 |     |     |     |       |     |     |     |     |
|                 | t   | (   | t   | (k    | (   |     |     |     |
|                 | ime | mb) | ime | t)^b^ | kt) |     |     |     |
|                 |     |     |     |       |     |     |     |     |
|                 | (U  |     | (U  |       |     |     |     |     |
|                 | TC) |     | TC) |       |     |     |     |     |
|                 |     |     | ^a^ |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Azores**      |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Santa Maria     | 2   | 99  | 2   | 49    | 71  |     |     |     |
| (LPAZ)          | 0/0 | 0.9 | 0/0 |       |     |     |     |     |
|                 | 800 |     | 800 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Ponta Delgada   | 2   | 99  | 2   | 25    | 44  |     |     |     |
|                 | 0/0 | 1.9 | 0/0 |       |     |     |     |     |
|                 | 700 |     | 800 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Spain**       |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Punta Candieira |     |     | 2   |       | 99  |     |     |     |
|                 |     |     | 1/? |       |     |     |     |     |
|                 |     |     | ??? |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Fisterra        |     |     | 2   |       | 89  |     |     |     |
|                 |     |     | 1/? |       |     |     |     |     |
|                 |     |     | ??? |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Cabo Vilán      |     |     | 2   |       | 82  |     |     |     |
|                 |     |     | 1/? |       |     |     |     |     |
|                 |     |     | ??? |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Ferrol          |     |     | 2   |       | 64  |     |     |     |
|                 |     |     | 1/? |       |     |     |     |     |
|                 |     |     | ??? |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| A Coruña        | 2   | 98  | 2   | 37    | 62  |     |     |     |
|                 | 1/0 | 8.0 | 1/0 |       |     |     |     |     |
|                 | 644 |     | 644 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Santiago        |     |     | 2   |       | 54  |     |     |     |
|                 |     |     | 1/? |       |     |     |     |     |
|                 |     |     | ??? |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Vigo            |     |     | 2   |       | 46  |     |     |     |
|                 |     |     | 1/? |       |     |     |     |     |
|                 |     |     | ??? |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **England**     |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| St. Mary's      |     |     | 2   |       | 60  |     |     |     |
| Airport, Scilly |     |     | 1/? |       |     |     |     |     |
| Island          |     |     | ??? |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
|                 |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
|                 |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+

^a^ Date/time is for sustained wind when both sustained and gust are
listed.

^b^ Wind averaging periods is 10 min.

^c^ Storm surge is water height above normal astronomical tide level.

^d^ Storm tide is water height above National Geodetic Vertical Datum
(1929 mean sea level).

Number range CHAPTERTable 4. Preliminary track forecast evaluation
(heterogeneous sample) for Hurricane Gordon, 10-20 September 2006.
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.

+---------+-------+-------+-------+-------+-------+-------+-------+
| Number  | For   |       |       |       |       |       |       |
| range   | ecast |       |       |       |       |       |       |
| C       | P     |       |       |       |       |       |       |
| HAPTERF | eriod |       |       |       |       |       |       |
| orecast | (h)   |       |       |       |       |       |       |
| Te      |       |       |       |       |       |       |       |
| chnique |       |       |       |       |       |       |       |
+=========+=======+=======+=======+=======+=======+=======+=======+
|         | 12    | 24    | 36    | 48    | 72    | 96    | 120   |
+---------+-------+-------+-------+-------+-------+-------+-------+
| CLP5    | 52    | 127   | 217   | 315   | 475   | 514   | 450   |
|         | (39)  | (37)  | (35)  | (33)  | (29)  | (25)  | (21)  |
+---------+-------+-------+-------+-------+-------+-------+-------+
| GFNI    | 28    | 57    | **85  | **121 | **225 | **297 | 363   |
|         | (34)  | (32)  | (     | (     | (     | (     | (15)  |
|         |       |       | 30)** | 28)** | 24)** | 20)** |       |
+---------+-------+-------+-------+-------+-------+-------+-------+
| GFDI    | **23  | **36  | **56  | **99  | 228   | 382   | 525   |
|         | (     | (     | (     | (     | (27)  | (23)  | (17)  |
|         | 37)** | 35)** | 33)** | 31)** |       |       |       |
+---------+-------+-------+-------+-------+-------+-------+-------+
| GFSI    | 33    | **48  | **71  | **104 | **203 | **304 | 364   |
|         | (35)  | (     | (     | (     | (     | (     | (10)  |
|         |       | 33)** | 33)** | 30)** | 24)** | 18)** |       |
+---------+-------+-------+-------+-------+-------+-------+-------+
| AEMI    | 40    | 65    | 93    | 147   | 301   | 391   | 563   |
|         | (36)  | (35)  | (33)  | (29)  | (24)  | (19)  | (15)  |
+---------+-------+-------+-------+-------+-------+-------+-------+
| NGPI    | 32    | 60    | 86    | **119 | **207 | **215 | **223 |
|         | (34)  | (32)  | (30)  | (     | (     | (     | (     |
|         |       |       |       | 28)** | 24)** | 20)** | 16)** |
+---------+-------+-------+-------+-------+-------+-------+-------+
| UKMI    | 52    | 96    | 136   | 198   | 403   | 553   | 611   |
|         | (35)  | (33)  | (31)  | (29)  | (21)  | (19)  | (16)  |
+---------+-------+-------+-------+-------+-------+-------+-------+
| A98E    | 41    | 69    | 111   | 166   | 264   | **322 | **351 |
|         | (38)  | (36)  | (35)  | (33)  | (29)  | (     | (     |
|         |       |       |       |       |       | 25)** | 21)** |
+---------+-------+-------+-------+-------+-------+-------+-------+
| A9UK    | 42    | 84    | 134   | 201   | 300   |       |       |
|         | (17)  | (16)  | (16)  | (16)  | (14)  |       |       |
+---------+-------+-------+-------+-------+-------+-------+-------+
| BAMD    | 37    | 66    | 113   | 169   | 312   | 431   | 485   |
|         | (38)  | (36)  | (35)  | (33)  | (29)  | (25)  | (21)  |
+---------+-------+-------+-------+-------+-------+-------+-------+
| BAMM    | 31    | 54    | **85  | 129   | **224 | **315 | 379   |
|         | (38)  | (36)  | (     | (33)  | (     | (     | (21)  |
|         |       |       | 35)** |       | 29)** | 25)** |       |
+---------+-------+-------+-------+-------+-------+-------+-------+
| BAMS    | 41    | 75    | 106   | 143   | **211 | **297 | **298 |
|         | (38)  | (36)  | (35)  | (33)  | (     | (     | (     |
|         |       |       |       |       | 29)** | 25)** | 21)** |
+---------+-------+-------+-------+-------+-------+-------+-------+
| CONU    | 28    | **49  | **74  | **114 | **203 | **299 | 368   |
|         | (37)  | (     | (     | (     | (     | (     | (16)  |
|         |       | 35)** | 33)** | 30)** | 25)** | 21)** |       |
+---------+-------+-------+-------+-------+-------+-------+-------+
| GUNA    | 28    | **49  | **75  | **110 | 238   | **306 | 392 ( |
|         | (32)  | (     | (     | (     | (19)  | (     | 9)    |
|         |       | 30)** | 30)** | 28)** |       | 15)** |       |
+---------+-------+-------+-------+-------+-------+-------+-------+
| FSSE    | **24  | **47  | **72  | **114 | 259   | 356   | 396   |
|         | (     | (     | (     | (     | (25)  | (21)  | (16)  |
|         | 35)** | 33)** | 31)** | 29)** |       |       |       |
+---------+-------+-------+-------+-------+-------+-------+-------+
| OFCL    | 28    | 54    | 86    | 129   | 227   | 332   | 361   |
|         | (38)  | (36)  | (34)  | (32)  | (27)  | (21)  | (19)  |
+---------+-------+-------+-------+-------+-------+-------+-------+
| NHC     | 37    | 65    | 91    | 118   | 171   | 231   | 303   |
| O       | (     | (     | (     | (     | (     | (913) | (742) |
| fficial | 1930) | 1743) | 1569) | 1410) | 1138) |       |       |
|         |       |       |       |       |       |       |       |
| (200    |       |       |       |       |       |       |       |
| 1-2005) |       |       |       |       |       |       |       |
| mean)   |       |       |       |       |       |       |       |
+---------+-------+-------+-------+-------+-------+-------+-------+

Table 5. Preliminary intensity forecast evaluation (heterogeneous
sample) for Hurricane Gordon, 10-20 September 2006. Forecast errors (kt)
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.

+--------+------+--------+--------+--------+--------+-------+-------+
| Number | Fore |        |        |        |        |       |       |
| range  | cast |        |        |        |        |       |       |
| CHA    | Pe   |        |        |        |        |       |       |
| PTERFo | riod |        |        |        |        |       |       |
| recast | (h)  |        |        |        |        |       |       |
| Tec    |      |        |        |        |        |       |       |
| hnique |      |        |        |        |        |       |       |
+========+======+========+========+========+========+=======+=======+
|        | 12   | 24     | 36     | 48     | 72     | 96    | 120   |
+--------+------+--------+--------+--------+--------+-------+-------+
| SHF5   | 7.2  | 11.4   | 14.8   | 17.6   | **20.6 | *     | *     |
|        | (39) | (37)   | (35)   | (33)   | (29)** | *19.7 | *10.7 |
|        |      |        |        |        |        | (     | (     |
|        |      |        |        |        |        | 25)** | 21)** |
+--------+------+--------+--------+--------+--------+-------+-------+
| GFDI   | *    | **9.0  | **12.2 | **15.7 | **13.6 | *     | *     |
|        | *5.9 | (35)** | (33)** | (31)** | (27)** | *10.4 | *10.4 |
|        | (3   |        |        |        |        | (     | (     |
|        | 7)** |        |        |        |        | 23)** | 17)** |
+--------+------+--------+--------+--------+--------+-------+-------+
| SHIP   | *    | **8.8  | **12.9 | 17.5   | 24.6   | 26.4  | 27.5  |
|        | *5.6 | (33)** | (32)** | (30)   | (29)   | (25)  | (21)  |
|        | (3   |        |        |        |        |       |       |
|        | 5)** |        |        |        |        |       |       |
+--------+------+--------+--------+--------+--------+-------+-------+
| DSHP   | *    | **8.8  | **12.9 | 17.5   | 24.6   | 26.4  | 27.5  |
|        | *5.6 | (33)** | (32)** | (30)   | (29)   | (25)  | (21)  |
|        | (3   |        |        |        |        |       |       |
|        | 5)** |        |        |        |        |       |       |
+--------+------+--------+--------+--------+--------+-------+-------+
| FSSE   | *    | **8.3  | **10.8 | **14.4 | **18.4 | 23.0  | 31.3  |
|        | *5.6 | (33)** | (31)** | (29)** | (25)** | (21)  | (16)  |
|        | (3   |        |        |        |        |       |       |
|        | 5)** |        |        |        |        |       |       |
+--------+------+--------+--------+--------+--------+-------+-------+
| ICON   | *    | **7.8  | **10.0 | **13.1 | **15.7 | *     | *     |
|        | *5.4 | (31)** | (30)** | (28)** | (27)** | *16.6 | *19.9 |
|        | (3   |        |        |        |        | (     | (     |
|        | 2)** |        |        |        |        | 23)** | 17)** |
+--------+------+--------+--------+--------+--------+-------+-------+
| OFCL   | 6.8  | 10.7   | 14.7   | 17.2   | 22.6   | 21.4  | 21.1  |
|        | (38) | (36)   | (34)   | (32)   | (27)   | (21)  | (19)  |
+--------+------+--------+--------+--------+--------+-------+-------+
| NHC    | 6.3  | 9.8    | 12.1   | 14.3   | 18.4   | 19.8  | 21.8  |
| Of     | (1   | (1743) | (1569) | (1410) | (1138) | (913) | (742) |
| ficial | 930) |        |        |        |        |       |       |
|        |      |        |        |        |        |       |       |
| (200   |      |        |        |        |        |       |       |
| 1-2005 |      |        |        |        |        |       |       |
| mean)  |      |        |        |        |        |       |       |
+--------+------+--------+--------+--------+--------+-------+-------+

Number range CHAPTERNumber range CHAPTERTable 6. Watch and warning
summary for Hurricane Gordon, 10-20 September 2006.

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

  18/2100     Tropical Storm Watch issued    The Azores

  19/0300     Tropical Storm Watch changed   The Azores
              to Hurricane Warning           

  20/0000     Hurricane Warning discontinued The Western Azores Islands of
                                             Corvo and Flores

  20/0600     Hurricane Warning discontinued The Central Azores

  20/1200     Hurricane Warning discontinued The Eastern Azores
  ----------- ------------------------------ -----------------------------

![](media/image1.wmf){width="7.497222222222222in"
height="5.795138888888889in"}

Number range CHAPTERFigure 1. Best track positions for Hurricane Gordon,
10-20 September 2006. Track during the extratropical stage is based on
analyses from the NOAA Ocean Prediction Center.

![](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 Gordon, 10-20
September 2006. 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. Objective Dvorak estimates represent
linear averages over a three-hour period centered on the nominal
observation time. Estimates during the extratropical stage are based on
analyses from the NOAA Ocean Prediction Center and QuikSCAT data.

![](media/image3.wmf){width="6.252083333333333in"
height="4.8277777777777775in"}

Number range CHAPTERFigure 3. Selected pressure observations and best
track minimum central pressure curve for Hurricane Gordon, 10-20
September 2006. Objective Dvorak estimates represent linear averages
over a three-hour period centered on the nominal observation time.
Estimates during the extratropical stage are based primarily on analyses
from the NOAA Ocean Prediction Center.

![](media/image4.png){width="6.495833333333334in"
height="6.495833333333334in"}

Figure 4. Visible satellite image from GOES-12 at 2015 UTC 13 September,
showing Gordon approaching peak intensity. Image courtesy of the Naval
Research Laboratory, Monterey, CA.Number range CHAPTER

Number range CHAPTER