Number range CHAPTERTropical Cyclone Report

Hurricane Isaac

(AL092006)

27 September-02 October 2006

Michelle Mainelli

National Hurricane Center

16 November 2006

Isaac was a category 1 hurricane (on the Saffir-Simpson Hurricane Scale)
that developed over the central Atlantic Ocean. Even though Isaac did
not make landfall, it produced tropical storm force winds over portions
of southeastern Newfoundland.

a.  Synoptic History

    Isaac developed from a tropical wave that exited the west coast of
    Africa on 18 September. An area of disturbed weather associated with
    this wave began to show signs of organization with some curved bands
    and deep convection on 23 September, while located about 900 n mi
    west of the Cape Verde Islands. The increased organization of
    convection led to the initiation of Dvorak classifications at 0600
    UTC that day. Convection pulsated for several days as the large
    disturbance moved west-northwestward under the influence of moderate
    to strong upper-level winds. After four days, and once the
    upper-level winds relaxed, the system was able to acquire sufficient
    organization to be designated as a tropical depression, while
    centered about 810 n mi east-southeast of Bermuda at 1800 UTC 27
    September. The "best track" chart of the tropical cyclone's path is
    given in Fig. 1, with the wind and pressure histories shown in Figs.
    2 and 3, respectively. The best track positions and intensities are
    listed in Table 1.

    The depression strengthened to a tropical storm around 0600 UTC 28
    September, about 12 h after the cyclone's formation. Initially, the
    cyclone moved northwestward between an upper-level low to its
    west-southwest and a low- to mid-level ridge to its east. Deep
    convection sputtered throughout the day, possibly due to cool water
    that had been upwelled there by both Hurricane's Gordon and Helene.
    In addition to the cooled waters, water vapor imagery indicated that
    some mid- to upper-level dry air had become entrained into Isaac's
    core and the cyclone appeared to have some subtropical
    characteristics with a baroclinic-type cloud-pattern and little
    convection near the core on 28 September. The next day, the cyclone
    began to move in a more west-northwestward motion in response to
    mid-level ridging over the central Atlantic. Isaac appeared to be
    more tropical as deep convection re-developed around the center and
    the cloud pattern became more consolidated. Vertical shear was also
    lessening, and in combination with the system moving away from the
    area of upwelled waters, Isaac began to strengthen. The favorable
    atmospheric and oceanic environment resulted in Isaac intensifying
    to hurricane status around 1200 UTC 30 September. This strengthening
    episode was short-lived and Isaac reached its peak intensity of 75
    kt around 0000 UTC 1 October, while centered about 285 n mi east of
    Bermuda.

    On 1 October, Isaac began to recurve around the western periphery of
    a subtropical ridge with an increase in forward speed. The cyclone
    moved quickly to the north-northeast on 2 October ahead of a
    deep-layer trough approaching from the west. During this time, Isaac
    encountered increasing southwesterly shear and cooler sea surface
    temperatures. By 1200 UTC that day, it weakened to a tropical storm.
    While racing toward the northeast around 35 kt on 2 October, Isaac
    passed about 35 n mi southeast of the Avalon Peninsula of
    Newfoundland late in the afternoon. Although Isaac remained
    offshore, tropical storm force winds were felt across portions of
    the southern Avalon Peninsula. Isaac maintained tropical cyclone
    status as it passed Newfoundland since it still possessed a core of
    strong winds and convection near the center. Thereafter, Isaac
    quickly transitioned to an extratropical cyclone by 0000 UTC 3
    October and merged with a larger extratropical low by 1800 UTC later
    that day.

b.  Meteorological Statistics

    Observations in Isaac (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 Isaac. Isaac was embedded in an area of high pressures
    throughout its lifetime, which caused the minimum pressures to be
    different than the Dvorak curve estimations as shown in Figure 3.

    Ship reports of winds of tropical storm force associated with Isaac
    are given in Table 2. The most noteworthy ship observation was 45-kt
    from the **Elektra** (call sign SIWB) at 0600 UTC 2 October. At that
    time, the **Elektra** was located about 150 n mi east of the center
    of Isaac.

    Isaac brought tropical storm conditions to portions of the southern
    Avalon Peninsula of Newfoundland during the afternoon and evening of
    2 October; selected surface observations from land stations, data
    buoys, and oil platforms are given in Table 3. The strongest winds
    reported on land occurred from the Cape Race Newfoundland station
    where sustained winds reached 40 kt and gusts reached 52 kt. There
    was also an observation from a private weather station at Cape Pine
    which reported a gust of 41 kt. Since the strongest winds associated
    with Isaac were located in the eastern semicircle over the offshore
    waters, the Avalon Peninsula had relatively light winds across most
    of the area. Moreover, the rapid forward motion of the tropical
    cyclone while it was passing southeast of Newfoundland resulted in
    modest rainfall amounts of one inch or less across the warned area.
    At 1500 UTC 2 October, the Canadian moored buoy 44138 reported
    sustained winds of 45 kt with gusts of 56 kt at a 5 m elevation.
    This observation was around 60 n mi east of the center of Isaac's
    circulation. At 0000 UTC 3 October, after extratropical transition,
    three oil platforms (HP6038, VEP717, and YJUF7) reported 48-56 kt
    sustained winds about 110 n mi east-southeast of the circulation
    center. It should be noted that the anemometer heights on these oil
    rigs are between 60 m and 90 m.

c.  Casualty and Damage Statistics

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

d.  Forecast and Warning Critique

    The potential development of Isaac was introduced into the Tropical
    Weather Outlook (TWO) on 20 September, about nine days prior to
    genesis. The system was described as "a tropical wave accompanied by
    a broad surface low pressure system". By early on 24 September, the
    system showed enough signs of organization that the potential of a
    depression forming was mentioned in the TWO. However, the low moved
    into an area of unfavorable upper-level winds over the next couple
    of days where the potential for further development lessened. By
    early on 26 September, the system reacquired enough organization to
    indicate the system had the potential, once again, to become a
    depression in the TWO, which was 42 hours prior to the first
    advisory issuance.

    A verification of official and guidance model track forecasts is
    given in Table 4. Average official track errors for Isaac were 29,
    51, 76, 115, 193, 317, and 574 n mi for the 12, 24, 36, 48, 72, 96,
    and 120 h forecasts, respectively. The number of forecasts ranged
    from 19 at 12 h to 1 at 120 h. These errors are lower than the
    average long-term official track errors during the 12 to 48 hour
    forecast periods but greater than average during the 3-day to 5-day
    forecast period (Table 4). The consensus models (GUNA/CONU/FSSE)
    performed quite well and had lower errors than the official
    forecasts. In particular, the FSSE had the lowest track errors of
    all the model guidance through 72 h. Most of the errors during the
    later time periods resulted from difficulties in forecasting the
    rapid increase in forward speed of the cyclone as it accelerated
    ahead of a large upper-trough. While the official track forecast
    errors were significantly higher than average, the sample size at
    these forecast times was quite small.

    Average official intensity errors were 4, 6, 8, 12, 17, 13, and 5 kt
    for the 12, 24, 36, 48, 72, 96, and 120 h forecasts, respectively
    (Table 5). For comparison, the average long-term official intensity
    errors are 6, 10, 12, 14, 18, 20, and 22 kt, respectively. The
    official intensity forecasts were better than all guidance models
    through 48 h and better than the average long-term errors at days 3
    through 5.

Watches and warnings associated with Isaac are listed in Table 6.

Acknowledgements:

Peter Bowyer and Chris Fogarty of the Canadian Hurricane Centre provided
the land, Canadian moored buoy, and Canadian oil platforms observations
that were used in this report.

Number range CHAPTERTable 1. Best track for Hurricane Isaac, 27
September -- 2 October 2006.

+---------+-----------+-----------+---------+---------+--------------+
| Da      | Latitude  | Longitude | P       | Wind    | Stage        |
| te/Time |           |           | ressure | Speed   |              |
|         | (^o^N)    | (^o^W)    |         |         |              |
| (UTC)   |           |           | (mb)    | (kt)    |              |
+---------+-----------+-----------+---------+---------+--------------+
| 27 /    | 26.1      | 52.6      | 1012    | 30      | tropical     |
| 1800    |           |           |         |         | depression   |
+---------+-----------+-----------+---------+---------+--------------+
| 28 /    | 26.8      | 53.4      | 1012    | 30      | \"           |
| 0000    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 28 /    | 27.4      | 54.0      | 1008    | 35      | tropical     |
| 0600    |           |           |         |         | storm        |
+---------+-----------+-----------+---------+---------+--------------+
| 28 /    | 28.0      | 54.4      | 1006    | 40      | \"           |
| 1200    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 28 /    | 28.6      | 54.6      | 1006    | 40      | \"           |
| 1800    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 29 /    | 28.9      | 54.9      | 1006    | 40      | \"           |
| 0000    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 29 /    | 29.0      | 55.4      | 1006    | 40      | \"           |
| 0600    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 29 /    | 29.2      | 55.8      | 1003    | 45      | \"           |
| 1200    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 29 /    | 29.5      | 56.5      | 1000    | 50      | \"           |
| 1800    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 30 /    | 29.8      | 57.1      | 997     | 60      | \"           |
| 0000    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 30 /    | 30.1      | 57.7      | 995     | 60      | \"           |
| 0600    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 30 /    | 30.6      | 58.5      | 992     | 65      | hurricane    |
| 1200    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 30 /    | 31.3      | 59.2      | 989     | 70      | \"           |
| 1800    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 01 /    | 32.0      | 59.8      | 987     | 75      | \"           |
| 0000    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 01 /    | 32.8      | 60.2      | 985     | 75      | \"           |
| 0600    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 01 /    | 33.8      | 60.3      | 986     | 70      | \"           |
| 1200    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 01 /    | 35.2      | 60.3      | 987     | 70      | \"           |
| 1800    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 02 /    | 37.2      | 59.6      | 988     | 65      | \"           |
| 0000    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 02 /    | 39.8      | 58.0      | 989     | 65      | \"           |
| 0600    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 02 /    | 42.5      | 56.2      | 990     | 60      | tropical     |
| 1200    |           |           |         |         | storm        |
+---------+-----------+-----------+---------+---------+--------------+
| 02 /    | 45.5      | 53.7      | 995     | 55      | \"           |
| 1800    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 03 /    | 47.6      | 51.0      | 996     | 55      | e            |
| 0000    |           |           |         |         | xtratropical |
+---------+-----------+-----------+---------+---------+--------------+
| 03 /    | 48.6      | 49.0      | 998     | 45      | \"           |
| 0600    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 03 /    | 49.5      | 47.0      | 1000    | 35      | \"           |
| 1200    |           |           |         |         |              |
+---------+-----------+-----------+---------+---------+--------------+
| 03 /    |           |           |         |         | merged with  |
| 1800    |           |           |         |         | e            |
|         |           |           |         |         | xtratropical |
|         |           |           |         |         | low          |
+---------+-----------+-----------+---------+---------+--------------+
| 01 /    | 32.0      | 59.8      | 985     | 75      | minimum      |
| 0000    |           |           |         |         | pressure     |
+---------+-----------+-----------+---------+---------+--------------+

Number range CHAPTERTable 2. Selected ship reports with winds of at
least 34 kt for Hurricane Isaac, 27 September -- 2 October 2006

+-----------+-----------+---------+----------+-----------+-----------+
| Date/Time | Ship call | L       | L        | Wind      | Pressure  |
|           | sign      | atitude | ongitude |           |           |
| (UTC)     |           |         |          | dir/speed | (mb)      |
|           |           | (^o^N)  | (^o^W)   | (kt)      |           |
+-----------+-----------+---------+----------+-----------+-----------+
| 02 / 0600 | SIWB      | 40.2    | 54.7     | 160 / 45  | 1016.6    |
+-----------+-----------+---------+----------+-----------+-----------+
| 03 / 0000 | DGSE      | 45.0    | 48.2     | 190 / 37  | 1014.0    |
+-----------+-----------+---------+----------+-----------+-----------+
| 03 / 0000 | WCZ654    | 46.5    | 48.2     | 190 / 40  | 1008.9    |
+-----------+-----------+---------+----------+-----------+-----------+

Number range CHAPTERTable 3. Selected surface observations for Hurricane
Isaac, 27 September -- 2 October 2006.

+----------------+-------+-----+-----+-------+----+-----+-----+-----+
| Location       | Mi    |     | M   |       |    | St  | St  | To  |
|                | nimum |     | axi |       |    | orm | orm | tal |
|                | Sea   |     | mum |       |    | su  |     |     |
|                | Level |     | S   |       |    | rge | t   | r   |
|                | Pre   |     | urf |       |    |     | ide | ain |
|                | ssure |     | ace |       |    | (   |     |     |
|                |       |     |     |       |    | ft) | (   | (   |
|                |       |     | W   |       |    | ^c^ | ft) | in) |
|                |       |     | ind |       |    |     | ^d^ |     |
|                |       |     | Sp  |       |    |     |     |     |
|                |       |     | eed |       |    |     |     |     |
+================+=======+=====+=====+=======+====+=====+=====+=====+
|                | Date/ | Pre | Da  | Sust  | Gu |     |     |     |
|                |       | ss. | te/ | ained | st |     |     |     |
|                | time  |     |     |       |    |     |     |     |
|                |       | (   | t   | (k    | (k |     |     |     |
|                | (UTC) | mb) | ime | t)^b^ | t) |     |     |     |
|                |       |     |     |       |    |     |     |     |
|                |       |     | (U  |       |    |     |     |     |
|                |       |     | TC) |       |    |     |     |     |
|                |       |     | ^a^ |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
| **             |       |     |     |       |    |     |     |     |
| Newfoundland** |       |     |     |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
| Cape Race      |       |     | 0   | 40    | 52 |     |     | 1.0 |
|                |       |     | 2/1 |       |    |     |     |     |
|                |       |     | 900 |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
| Cape Pine      |       |     | 0   |       | 41 |     |     |     |
|                |       |     | 2/1 |       |    |     |     |     |
|                |       |     | 700 |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
|                |       |     |     |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
| **Buoys**      |       |     |     |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
| Canadian       | 02 /  | 99  | 0   | 45    | 56 |     |     |     |
| moored buoy    | 1600  | 9.9 | 2/1 |       |    |     |     |     |
| 44138 (44.3N   |       |     | 500 |       |    |     |     |     |
| 53.6W)         |       |     |     |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
| Canadian       |       |     | 0   |       | 35 |     |     |     |
| moored buoy    |       |     | 2/1 |       |    |     |     |     |
|                |       |     | 700 |       |    |     |     |     |
| 44140 (43.8N   |       |     |     |       |    |     |     |     |
| 51.7W)         |       |     |     |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
| Canadian       | 02    | 100 | 0   |       | 35 |     |     |     |
| moored buoy    | /1900 | 1.1 | 2/1 |       |    |     |     |     |
|                |       |     | 900 |       |    |     |     |     |
| 44251 (46.4N   |       |     |     |       |    |     |     |     |
| 53.4W)         |       |     |     |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
|                |       |     |     |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
| **Grand Banks  |       |     |     |       |    |     |     |     |
| Oil            |       |     |     |       |    |     |     |     |
| Platforms**    |       |     |     |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
| HP6038         | 03    | 100 | 0   | 48    |    |     |     |     |
|                | /0000 | 9.2 | 3/0 |       |    |     |     |     |
|                |       |     | 000 |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
| VEP717         | 03    | 100 | 0   | 56    |    |     |     |     |
|                | /0000 | 6.8 | 2/2 |       |    |     |     |     |
|                |       |     | 100 |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+
| YJUF7          | 03    | 100 | 0   | 52    |    |     |     |     |
|                | /0000 | 8.7 | 3/0 |       |    |     |     |     |
|                |       |     | 000 |       |    |     |     |     |
+----------------+-------+-----+-----+-------+----+-----+-----+-----+

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

^b^ Except as noted, sustained wind averaging periods for C-MAN and
land-based reports are 2 min; Canadian buoy averaging periods are 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 Isaac, 27 September -- 2 October
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 |       |       |       |       |       |       |
| CHAPTE    | P     |       |       |       |       |       |       |
| RForecast | eriod |       |       |       |       |       |       |
| Technique | (h)   |       |       |       |       |       |       |
+===========+=======+=======+=======+=======+=======+=======+=======+
|           | 12    | 24    | 36    | 48    | 72    | 96    | 120   |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CLP5      | 52    | 125   | 207   | 277   | 403 ( | 415 ( | **450 |
|           | (19)  | (17)  | (15)  | (13)  | 9)    | 5)    | (     |
|           |       |       |       |       |       |       | 1)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFNI      | 29    | **49  | 83    | 130 ( | 228 ( | 448 ( |       |
|           | (17)  | (     | (11)  | 9)    | 5)    | 1)    |       |
|           |       | 13)** |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDI      | 35    | 61    | 88    | **107 | **153 | **193 |       |
|           | (18)  | (16)  | (14)  | (     | (     | (     |       |
|           |       |       |       | 12)** | 8)**  | 4)**  |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFSI      | 46    | 78    | 109   | 143   | 240 ( | **265 |       |
|           | (16)  | (15)  | (13)  | (11)  | 3)    | (     |       |
|           |       |       |       |       |       | 1)**  |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| AEMI      | 59    | 94    | 117   | 121   | **118 |       |       |
|           | (18)  | (16)  | (14)  | (12)  | (     |       |       |
|           |       |       |       |       | 7)**  |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NGPI      | 29    | **46  | **66  | **107 | **172 | **200 |       |
|           | (17)  | (     | (     | (     | (     | (     |       |
|           |       | 15)** | 13)** | 11)** | 7)**  | 3)**  |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| UKMI      | 46    | 69    | **72  | 125   | **145 | **102 |       |
|           | (17)  | (15)  | (     | (11)  | (     | (     |       |
|           |       |       | 13)** |       | 7)**  | 3)**  |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| A98E      | 37    | 64    | 92    | **111 | **168 | **298 | **132 |
|           | (19)  | (17)  | (15)  | (     | (     | (     | (     |
|           |       |       |       | 13)** | 9)**  | 5)**  | 1)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| A9UK      | 36 (  | 67 (  | 101 ( | 145 ( | **160 |       |       |
|           | 9)    | 8)    | 7)    | 6)    | (     |       |       |
|           |       |       |       |       | 4)**  |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMD      | 35    | 56    | 88    | 120   | **178 | **278 | **367 |
|           | (18)  | (16)  | (14)  | (12)  | (     | (     | (     |
|           |       |       |       |       | 8)**  | 5)**  | 1)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMM      | 43    | 77    | 113   | 143   | **191 | 343 ( | **118 |
|           | (18)  | (16)  | (14)  | (12)  | (     | 5)    | (     |
|           |       |       |       |       | 8)**  |       | 1)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMS      | 65    | 119   | 165   | 195   | 198 ( | **232 | **152 |
|           | (18)  | (16)  | (14)  | (12)  | 8)    | (     | (     |
|           |       |       |       |       |       | 5)**  | 1)**  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CONU      | 29    | **44  | **59  | **83  | **120 | **148 |       |
|           | (17)  | (     | (     | (     | (     | (     |       |
|           |       | 15)** | 13)** | 11)** | 7)**  | 3)**  |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GUNA      | **28  | **46  | **58  | **82  | **105 | **117 |       |
|           | (     | (     | (     | (     | (     | (     |       |
|           | 16)** | 15)** | 13)** | 11)** | 3)**  | 1)**  |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| FSSE      | **27  | **37  | **48  | **66  | **109 | **145 |       |
|           | (     | (     | (     | (     | (     | (     |       |
|           | 16)** | 14)** | 12)** | 10)** | 6)**  | 2)**  |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | 29    | 51    | 76    | 115   | 193 ( | 317 ( | 574 ( |
|           | (19)  | (17)  | (15)  | (13)  | 9)    | 5)    | 1)    |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 37    | 65    | 91    | 118   | 171   | 231   | 303   |
| Official  |       |       |       |       |       |       |       |
|           | \(1   | \(1   | \(1   | \(1   | \(1   | \(    | \(    |
| (         | 930\) | 743\) | 569\) | 410\) | 138\) | 913\) | 742\) |
| 2001-2005 |       |       |       |       |       |       |       |
| mean)     |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

Table 5. Preliminary intensity forecast evaluation (heterogeneous
sample) for Hurricane Isaac, 27 September -- 2 October 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   | For   |        |       |        |       |       |       |
| range    | ecast |        |       |        |       |       |       |
| CHAPTER  | P     |        |       |        |       |       |       |
| Forecast | eriod |        |       |        |       |       |       |
| T        | (h)   |        |       |        |       |       |       |
| echnique |       |        |       |        |       |       |       |
+==========+=======+========+=======+========+=======+=======+=======+
|          | 12    | 24     | 36    | 48     | 72    | 96    | 120   |
+----------+-------+--------+-------+--------+-------+-------+-------+
| SHF5     | 4.7   | 6.9    | 10.3  | 11.8   | *     | **4.6 | **4.0 |
|          | (19)  | (17)   | (15)  | (13)   | *11.7 | (     | (     |
|          |       |        |       |        | (     | 5)**  | 1)**  |
|          |       |        |       |        | 9)**  |       |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| GFDI     | 5.4   | 10.1   | 14.5  | 18.3   | 16.9  | 13.3  |       |
|          | (18)  | (16)   | (14)  | (12)   | ( 8)  | ( 4)  |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| SHIP     | 5.1   | 8.9    | 13.4  | 16.8   | 18.3  | 13.4  | **2.0 |
|          | (19)  | (17)   | (15)  | (13)   | ( 9)  | ( 5)  | (     |
|          |       |        |       |        |       |       | 1)**  |
+----------+-------+--------+-------+--------+-------+-------+-------+
| DSHP     | 5.1   | 8.9    | 13.4  | 16.8   | 18.3  | 13.4  | **2.0 |
|          | (19)  | (17)   | (15)  | (13)   | ( 9)  | ( 5)  | (     |
|          |       |        |       |        |       |       | 1)**  |
+----------+-------+--------+-------+--------+-------+-------+-------+
| FSSE     | 4.9   | 9.3    | 12.9  | 16.0   | *     | **6.5 |       |
|          | (16)  | (14)   | (12)  | (10)   | *10.8 | (     |       |
|          |       |        |       |        | (     | 2)**  |       |
|          |       |        |       |        | 6)**  |       |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| ICON     | 5.5   | 9.6    | 13.2  | 16.8   | *     | *     |       |
|          | (18)  | (16)   | (14)  | (12)   | *15.6 | *11.0 |       |
|          |       |        |       |        | (     | (     |       |
|          |       |        |       |        | 8)**  | 4)**  |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| OFCL     | 3.7   | 5.9    | 7.7   | 11.5   | 16.7  | 13.0  | 5.0 ( |
|          | (19)  | (17)   | (15)  | (13)   | ( 9)  | ( 5)  | 1)    |
+----------+-------+--------+-------+--------+-------+-------+-------+
| NHC      | 6.3   | 9.8    | 12.1  | 14.3   | 18.4  | 19.8  | 21.8  |
| Official |       |        | (     | (1410) | (     |       |       |
|          | \(1   | \(     | 1569) |        | 1138) | \(    | \(    |
| (2       | 930\) | 1743\) |       |        |       | 913\) | 742\) |
| 001-2005 |       |        |       |        |       |       |       |
| mean)    |       |        |       |        |       |       |       |
+----------+-------+--------+-------+--------+-------+-------+-------+

Number range CHAPTERTable 6. Watch and warning summary for Hurricane
Isaac, 27 September -- 2 October 2006.

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

  01 / 0740   Tropical Storm Watch issued    Avalon Peninsula, Newfoundland

  02 / 0900   Tropical Storm Watch upgraded  Avalon Peninsula
              to Tropical Storm Warning      

  02 / 0900   Tropical Storm Watch issued    Burin Peninsula and Bonavista
                                             Peninsula, Newfoundland

  02 / 1800   Tropical Storm Watch           Burin Peninsula and Bonavista
              discontinued                   Peninsula

  02 / 2100   Tropical Storm Warning         Avalon Peninsula
              discontinued                   
  ----------- ------------------------------ ------------------------------

> Number range CHAPTER![](media/image1.wmf){width="7.125694444444444in"
> height="5.490277777777778in"}
>
> Figure 1. Best track positions for Hurricane Isaac, 27 September -- 2
> October 2006. Track during the extratropical stage is partly based on
> analyses from the NOAA Ocean Prediction Center and the Canadian
> Hurricane Centre.
>
> Number range CHAPTER
>
> ![](media/image2.wmf){width="7.097222222222222in"
> height="4.819444444444445in"}
>
> Figure 2. Selected wind observations and best track maximum sustained
> surface wind speed curve for Hurricane Isaac, 27 September -- 2
> October 2006. Objective Dvorak estimates represent linear averages
> over a three-hour period centered on the nominal observation time.
> Estimates during the extratropical stage are partly based on analyses
> from both the NOAA Ocean Prediction Center and Canadian Hurricane
> Centre.
>
> Number range CHAPTER

![](media/image3.wmf){width="6.749305555555556in"
height="4.582638888888889in"}

> Figure 3. Selected pressure observations and best track minimum
> central pressure curve for Hurricane Isaac, 27 September -- 2 October
> 2006. Objective Dvorak estimates represent linear averages over a
> three-hour period centered on the nominal observation time. Estimates
> during the extratropical stage are partly based on analyses from both
> the NOAA Ocean Prediction Center and Canadian Hurricane Centre.

Number range CHAPTER