Number range CHAPTERTropical Cyclone Report

Subtropical Storm Andrea

(AL012007)

9-11 May 2007

Jamie R. Rhome, Jack Beven, and Mark Willis

National Hurricane Center

1 June 2007

Andrea formed off the southeast coast of the United States. It was the
eighth earliest cyclone since 1851 and the first May cyclone since 1981.

a.  Synoptic History

    Andrea formed from a large extratropical cyclone that originated
    just offshore the mid-Atlantic United States coast on 6 May. This
    pre-Andrea cyclone deepened steadily that day, with the central
    pressure falling 16 mb in the 24-hour period ending at 0600 UTC 7
    May. The cyclone initially possessed the classic signature of a
    fully mature extratropical system, with the associated cold front
    pushing through Florida and reaching as far south as Cuba on 7 May.
    By late on 7 May, the extratropical cyclone lost most of its
    baroclinic support and development ended. However, interaction of
    the low and strong high pressure to the north produced
    hurricane-force winds. The resulting large area of high winds, along
    with the slow motion of the extratropical low, generated large waves
    that impacted much of the coast of the southeastern United States
    and the Bahamas Islands. On 8 May, the low weakened and began
    drifting westward over progressively warmer waters in the western
    Atlantic. Along this track, vertical shear also decreased allowing
    for the generation of deeper convection around the center. By early
    on 9 May, convection had become symmetric about the low-level
    circulation center, the cyclone had lost all of its frontal and cold
    core structure, and the wind field had contracted. It is estimated
    that the system transformed into a subtropical cyclone by 0600 UTC 9
    May while centered about 150 n mi east of Jacksonville, Florida. The
    "best track" chart of the subtropical 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 cyclone's weakening continued during the subtropical phase, so
    Andrea's peak intensity of 50 kt occurred at 0600 UTC 9 May.
    Initially, Andrea was trapped within the retrograding
    middle-to-upper-tropospheric cutoff low that had caused the
    pre-Andrea extratratropical cyclogenesis. This pattern resulted in
    relatively weak shear and a slow westward drift of the cyclone. By
    late on 9 May, Andrea came under the influence of strong northerly
    flow aloft on the western side of the upper-level low, resulting in
    increasing vertical shear and a slow southward motion. The increase
    in vertical shear displaced the strongest convection southeast of
    the low-level center, and Andrea weakened to a depression by 1200
    UTC 10 May while centered about 95 n mi east-southeast of
    Jacksonville, Florida. Lacking significant deep convection, Andrea
    degenerated into a remnant low by 0000 UTC 11 May. The remnants of
    Andrea produced intermittent bursts of deep convection on 11 May
    while drifting southward just off the central coast of Florida.
    However, this activity was transient and never acquired sufficient
    organization for advisories to be re-initiated. The remnant low
    accelerated northeastward on 12-13 May ahead of an advancing cold
    front and later became absorbed within the frontal boundary by 14
    May.

b.  Meteorological Statistics

    Observations in Andrea (Figs. 2 and 3) include satellite-based
    Herbert-Poteat and Dvorak technique intensity estimates from the
    Tropical Analysis and Forecast Branch (TAFB) and the Satellite
    Analysis Branch (SAB), as well as flight-level and dropwindsonde
    observations from two 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 Andrea. Ship reports of winds of tropical storm force
    associated with Andrea are given in Table 2, and selected surface
    observations from land stations and data buoys are given in Table 3.
    Andrea's estimated peak intensity of 50 kt as a subtropical cyclone
    near 0600 UTC 9 May is based mainly on QuikSCAT data. The peak wind
    of 65 kt during the extratropical phase is based on buoy 41001
    located, approximate 150 n mi east of Cape Hatteras, which reported
    a maximum sustained wind of 55 kt with a gust to 70 kt at 0500 UTC 7
    May.

The basis for Andrea's designation as a subtropical cyclone beginning
0600 UTC 9 May includes conventional satellite imagery, nearby ship
observations, and remotely-sensed ocean surface vector winds from
QuikSCAT. Dropwindsondes obtained from the Air Force Hurricane Hunter
aircraft flown on the morning of 9 May indicate that Andrea had no
appreciable horizontal thermal gradients (Figure 4a) and was beginning
to acquire warm core characteristics. Specifically, the vertical wind
profiles displayed in Figure 4a show winds decreasing with height east
of the center, a pattern indicative of a warm core cyclone, with winds
increasing with height west of the center, a pattern indicative of a
cold core cyclone. Conventional satellite infrared satellite imagery
showed convection had become symmetric about the circulation center
(Figure 4b), and surface observations and ocean surface vector winds
from QuikSCAT showed that the radius of strongest winds had contracted
to within 60 n mi of the center (Figure 5).

Rainfall totals over the southeastern United States were generally less
than 1 inch and no flooding was reported.

Number range CHAPTER

c.  Casualty and Damage Statistics

    There were no reports of deaths directly attributable to Andrea as a
    subtropical storm. However, the pre-Andrea extratropical cyclone was
    directly responsible for 6 deaths including all four crew members of
    the 54-foot sailing vessel *Flying Colours* whose last known
    location was off the coast of North Carolina on 7 May, a kayaker who
    died after being pulled out to sea near Seabrook Island, South
    Carolina on 8 May, and a surfer who drowned after being overtaken by
    a large wave near New Smyrna Beach, Florida on 9 May. Even though
    the drowning on 9 May occurred a few hours after the designation of
    Andrea as subtropical cyclone, most of the wave energy responsible
    for this death was generated during the pre-Andrea extratropical
    phase. Additionally, the U.S. Coast Guard rescued 9 people from
    three sailboats off the coast of North Carolina on 7 May.

    Since Andrea never made landfall, most of the resulting damage was
    associated with the generation of large waves, higher than normal
    astronomical tides and associated coastal flooding, and associated
    beach erosion. Most of the significant damage occurred from North
    Carolina through Florida on 6-8 May as a result of very strong winds
    and waves associated with the pre-Andrea extratropical cyclone. A
    storm surge of 2-3 ft was reported in St. Johns and Flagler Counties
    in northeastern Florida.

    The vessel *Paris Express* encountered high seas in the Atlantic
    late on 6 May while en route from Savannah to Norfolk, resulting in
    the loss of 21 containers overboard. The resulting debris washed
    ashore from Cape Lookout, North Carolina northward to the Virginia
    border during the following days.

d.  Forecast and Warning Critique

    Since Tropical Weather Outlooks are not issued by the National
    Hurricane Center prior to June 1 (the "official" start of the
    Atlantic hurricane season), an assessment of genesis forecasts
    within that product is not possible. However, the pre-Andrea
    extratropical cyclone, including its associated hazards, was
    discussed by the National Hurricane Center within several Special
    Tropical Disturbance Statements beginning with the first issuance on
    the morning of 8 May.

    A verification of official and guidance model track forecasts is
    given in Table 4. Average official track errors for Andrea were 22,
    46, and 67 n mi for the 12, 24, and 36 h forecasts, respectively.
    For comparison, the average long-term official track errors are 35,
    61, and 86 n mi for the 12, 24, and 36 h forecasts, respectively. A
    verification of official and guidance model intensity forecasts is
    given in Table 5. Average official intensity errors were 1, 5, and 1
    kt for the 12, 24, and 36 h forecasts, respectively. For comparison,
    the average long-term official intensity errors are 6, 10, and 12
    kt, respectively. Both the official track and intensity forecasts
    were below the average long-term errors.

    A summary of watches and warnings issued during Andrea is given in
    Table 6.

e.  Acknowledgements

Ethan Gibney is acknowledged for creating the best track map.

Number range CHAPTERTable 1. Best track for Subtropical Storm Andrea
9-11 May 2007.

+----------+--------+--------+---------+-----------+-----------------+
| D        | La     | Lon    | P       | Wind      | Stage           |
| ate/Time | titude | gitude | ressure | Speed     |                 |
|          |        |        |         |           |                 |
| (UTC)    | (°N)   | (°W)   | (mb)    | (kt)      |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 06 /     | 35.5   | 74.0   | 1012    | 35        | extratropical   |
| 1200     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 06 /     | 35.0   | 73.0   | 1009    | 40        | \"              |
| 1800     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 07 /     | 34.3   | 71.7   | 1005    | 50        | \"              |
| 0000     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 07 /     | 33.3   | 72.3   | 998     | 65        | \"              |
| 0600     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 07 /     | 32.3   | 73.1   | 998     | 65        | \"              |
| 1200     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 07 /     | 31.5   | 74.0   | 998     | 65        | \"              |
| 1800     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 08 /     | 31.0   | 74.9   | 1000    | 55        | \"              |
| 0000     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 08 /     | 30.7   | 76.0   | 1001    | 50        | \"              |
| 0600     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 08 /     | 30.4   | 77.2   | 1001    | 50        | \"              |
| 1200     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 08 /     | 30.4   | 77.9   | 1001    | 50        | \"              |
| 1800     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 09 /     | 30.6   | 78.3   | 1001    | 50        | \"              |
| 0000     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 09 /     | 30.8   | 78.7   | 1001    | 50        | subtropical     |
| 0600     |        |        |         |           | storm           |
+----------+--------+--------+---------+-----------+-----------------+
| 09 /     | 30.9   | 79.2   | 1002    | 45        | \"              |
| 1200     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 09 /     | 30.9   | 79.6   | 1003    | 40        | \"              |
| 1800     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 10 /     | 30.7   | 79.8   | 1003    | 40        | \"              |
| 0000     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 10 /     | 30.5   | 79.9   | 1003    | 35        | \"              |
| 0600     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 10 /     | 30.1   | 79.9   | 1003    | 30        | subtropical     |
| 1200     |        |        |         |           | depression      |
+----------+--------+--------+---------+-----------+-----------------+
| 10 /     | 29.7   | 79.8   | 1003    | 30        | \"              |
| 1800     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 11 /     | 29.4   | 79.8   | 1004    | 30        | \"              |
| 0000     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 11 /     | 29.1   | 79.8   | 1004    | 30        | remnant low     |
| 0600     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 11 /     | 28.8   | 79.7   | 1006    | 25        | \"              |
| 1200     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 11 /     | 28.5   | 79.5   | 1007    | 25        | \"              |
| 1800     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 12 /     | 28.5   | 79.1   | 1007    | 25        | \"              |
| 0000     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 12 /     | 28.8   | 78.8   | 1006    | 25        | \"              |
| 0600     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 12 /     | 29.1   | 78.5   | 1005    | 25        | \"              |
| 1200     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 12 /     | 29.4   | 78.0   | 1006    | 25        | \"              |
| 1800     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 13 /     | 29.7   | 77.2   | 1006    | 25        | \"              |
| 0000     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 13 /     | 30.1   | 76.0   | 1006    | 25        | \"              |
| 0600     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 13 /     | 30.8   | 74.2   | 1007    | 25        | \"              |
| 1200     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 13 /     | 31.4   | 71.9   | 1007    | 25        | \"              |
| 1800     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 14 /     | 31.8   | 69.4   | 1007    | 25        | \"              |
| 0000     |        |        |         |           |                 |
+----------+--------+--------+---------+-----------+-----------------+
| 14 /     |        |        |         |           | absorbed by     |
| 0600     |        |        |         |           | front           |
+----------+--------+--------+---------+-----------+-----------------+
| 09 /     | 30.8   | 78.7   | 1001    | 50        | minimum         |
| 0600     |        |        |         |           | pressure        |
+----------+--------+--------+---------+-----------+-----------------+

Number range CHAPTERTable 2. Selected ship reports with winds of at
least 34 kt for Subtropical Storm Andrea 9-11 May 2007.

+-----------+-----------+-----------+-----------+-----------+-----------+
| Date/Time | Ship call | Latitude  | Longitude | Wind      | Pressure  |
| (UTC)     | sign      |           |           |           |           |
|           |           | (°N)      | (°W)      | dir/speed | (mb)      |
|           |           |           |           | (kt)      |           |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 09 / 0631 | SPAG1     | 31.4      | 80.6      | 350 / 39  |           |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 09 / 0700 | WFJN      | 32.7      | 75.8      | 140 / 35  | 1013.0    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 09 / 1800 | WBVY      | 32.1      | 79.5      | 090 / 37  | 1005.5    |
+-----------+-----------+-----------+-----------+-----------+-----------+

Number range CHAPTERTable 3. Selected surface observations for
Subtropical Storm Andrea, 9-11 May, 2007.

+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| 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^ |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Florida**     |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Official**    |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Jacksonville    | 0   | 100 | 1   | 22    | 37  |     |     | 0   |
| (KJAX)          | 9/2 | 7.9 | 0/1 |       |     |     |     | .17 |
|                 | 258 |     | 328 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Craig Municipal | 0   | 100 | 0   |       | 26  |     |     | 0   |
| Airport (KCRG)  | 9/2 | 7.8 | 9/2 |       |     |     |     | .32 |
|                 | 253 |     | 044 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Mayport Naval   | 0   | 100 | 1   |       | 33  |     |     | 0   |
| Base (KNRB)     | 9/2 | 7.8 | 0/1 |       |     |     |     | .36 |
|                 | 249 |     | 416 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| St. Augustine   | 0   | 100 | 1   |       | 30  |     |     | 0   |
| (KSGJ)          | 9/2 | 8.1 | 0/1 |       |     |     |     | .15 |
|                 | 250 |     | 450 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Flagler County  |     |     | 1   |       | 29  |     |     |     |
| Airport (KX47)  |     |     | 0/1 |       |     |     |     |     |
|                 |     |     | 418 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Fernandina      | 0   | 100 | 0   | 22    | 27  | 2   | 7   | 0   |
| Beach (FRBF1)   | 9/2 | 7.3 | 9/2 |       |     | .64 | .88 | .37 |
|                 | 218 |     | 248 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Mayport (MYPF1) | 0   | 100 | 1   | 24    | 33  | 2   | 6   |     |
|                 | 9/2 | 8.1 | 0/1 |       |     | .50 | .25 |     |
|                 | 230 |     | 400 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Hastings        |     |     |     |       |     |     |     | 0   |
| (HTGF1)         |     |     |     |       |     |     |     | .10 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Palm Coast      |     |     |     |       |     |     |     | 0   |
| (WOGF1)         |     |     |     |       |     |     |     | .08 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Jacksonville    |     |     |     |       |     |     |     | 0   |
| Beach (JAKF1)   |     |     |     |       |     |     |     | .77 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
|                 |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Georgia**     |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **Official**    |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| St. Simons      | 0   | 100 | 1   | 35    |     |     |     | 0   |
| Island (KSSI)   | 9/1 | 7.1 | 0/1 |       |     |     |     | .07 |
|                 | 608 |     | 458 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Brunswick       |     |     |     |       |     |     |     | 0   |
| (BRUG1)         |     |     |     |       |     |     |     | .42 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Woodbine        |     |     |     |       |     |     |     | 0   |
| (WBNG1)         |     |     |     |       |     |     |     | .57 |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| St. Simons      |     |     |     |       |     | 2   | 8   |     |
| Island NOS      |     |     |     |       |     | .83 | .09 |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
|                 |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| **NOAA          |     |     |     |       |     |     |     |     |
| Buoy/C-Man**    |     |     |     |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| St. Augustine   | 1   | 100 | 0   | 30    | 37  |     |     |     |
| Buoy (41012)    | 0/0 | 4.4 | 9/0 |       |     |     |     |     |
|                 | 850 |     | 600 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| St. Augustine   | 1   | 100 | 1   | 30    | 36  |     |     |     |
| Pier (SAUF1)    | 0/0 | 8.1 | 0/1 |       |     |     |     |     |
|                 | 800 |     | 510 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Gray's Reef     |     |     | 0   |       | 37  |     |     |     |
| Buoy (41008)    |     |     | 9/0 |       |     |     |     |     |
|                 |     |     | 600 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Canaveral East  |     |     | 0   |       | 33  |     |     |     |
| Buoy (41010)    |     |     | 9/0 |       |     |     |     |     |
|                 |     |     | 700 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+
| Edisto Buoy     |     |     | 0   |       | 39  |     |     |     |
| (41004)         |     |     | 9/1 |       |     |     |     |     |
|                 |     |     | 300 |       |     |     |     |     |
+-----------------+-----+-----+-----+-------+-----+-----+-----+-----+

^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 ASOS reports are 2 min; buoy averaging periods are 8 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 Subtropical Storm Andrea, 9-11 May 2007.
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      | 39 (  | 109 ( | 201 ( |       |       |       |       |
|           | 6)    | 4)    | 2)    |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFNI      | **19  | **29  |       |       |       |       |       |
|           | (     | (     |       |       |       |       |       |
|           | 3)**  | 1)**  |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDI      | 23 (  | **44  | 80 (  |       |       |       |       |
|           | 5)    | (     | 1)    |       |       |       |       |
|           |       | 3)**  |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFSI      | **19  | **39  | **65  |       |       |       |       |
|           | (     | (     | (     |       |       |       |       |
|           | 5)**  | 3)**  | 1)**  |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| AEMI      | **15  | **27  | **32  |       |       |       |       |
|           | (     | (     | (     |       |       |       |       |
|           | 5)**  | 3)**  | 1)**  |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NGPI      | **21  | **45  | **45  |       |       |       |       |
|           | (     | (     | (     |       |       |       |       |
|           | 6)**  | 4)**  | 2)**  |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| UKMI      | 34 (  | 69 (  |       |       |       |       |       |
|           | 4)    | 2)    |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMD      | **12  | **35  | 68 (  |       |       |       |       |
|           | (     | (     | 2)    |       |       |       |       |
|           | 6)**  | 4)**  |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMM      | 29 (  | 76 (  | 129 ( |       |       |       |       |
|           | 6)    | 4)    | 2)    |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMS      | 55 (  | 111 ( | 185 ( |       |       |       |       |
|           | 6)    | 4)    | 2)    |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CONU      | **18  | **39  | **54  |       |       |       |       |
|           | (     | (     | (     |       |       |       |       |
|           | 5)**  | 3)**  | 1)**  |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GUNA      | 22 (  | **43  |       |       |       |       |       |
|           | 4)    | (     |       |       |       |       |       |
|           |       | 2)**  |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | 22 (  | 46 (  | 67 (  |       |       |       |       |
|           | 5)    | 3)    | 1)    |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 35    | 61    | 86    | 112   | 162   | 221   | 290   |
| Official  |       |       |       |       |       |       |       |
|           | \(1   | \(1   | \(1   | \(1   | \(1   | \(    | \(    |
| (         | 852\) | 686\) | 519\) | 362\) | 100\) | 885\) | 723\) |
| 2002-2006 |       |       |       |       |       |       |       |
| mean)     |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

Table 5. Preliminary intensity forecast evaluation (heterogeneous
sample) for Subtropical Storm Andrea, 9-11 May 2007. 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 |       |       |       |       |       |       |
| CHAPTE    | P     |       |       |       |       |       |       |
| RForecast | eriod |       |       |       |       |       |       |
| Technique | (h)   |       |       |       |       |       |       |
+===========+=======+=======+=======+=======+=======+=======+=======+
|           | 12    | 24    | 36    | 48    | 72    | 96    | 120   |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| SHF5      | 4.2 ( | **3.0 | 7.0 ( |       |       |       |       |
|           | 6)    | (     | 2)    |       |       |       |       |
|           |       | 4)**  |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDI      | 4.4 ( | **4.0 | 12.0  |       |       |       |       |
|           | 5)    | (     | ( 1)  |       |       |       |       |
|           |       | 3)**  |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| SHIP      | 3.7 ( | 6.3 ( | 15.0  |       |       |       |       |
|           | 6)    | 4)    | ( 2)  |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| DSHP      | 3.7 ( | 6.3 ( | 15.0  |       |       |       |       |
|           | 6)    | 4)    | ( 2)  |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| ICON      | 3.2 ( | **2.7 | **2.0 |       |       |       |       |
|           | 5)    | (     | (     |       |       |       |       |
|           |       | 3)**  | 1)**  |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | **1.0 | 5.0 ( | 5.0 ( |       |       |       |       |
|           | (     | 3)    | 1)    |       |       |       |       |
|           | 5)**  |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 6.4   | 9.8   | 12.0  | 14.1  | 18.3  | 19.8  | 21.8  |
| Official  |       | (     | (     | (     | (     |       |       |
|           | \(1   | 1686) | 1519) | 1362) | 1100) | \(    | \(    |
| (         | 852\) |       |       |       |       | 885\) | 723\) |
| 2002-2006 |       |       |       |       |       |       |       |
| mean)     |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

Number range CHAPTERTable 6. Watch and warning summary for Subtropical
Storm Andrea, 9-11 May 2007.

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

  09 / 1500   Tropical Storm Watch issued    Altahama Sound to Flagler
                                             Beach

  10 / 1500   Tropical Storm Watch           Altahama Sound to Flagler
              discontinued                   Beach
  ----------- ------------------------------ ------------------------------

> ![](media/image1.jpeg){width="7.875694444444444in"
> height="6.085416666666666in"}
>
> Number range CHAPTERFigure 1. Best track positions for Subtropical
> Storm Andrea, 9-11 May 2007. Track during the extratropical stage is
> based partially on analyses from the Ocean Prediction Center.
>
> 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 Subtropical Storm Andrea, 9-11 May 2007.
> 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. Estimates during the extratropical stage are
> based partially on analyses from the Ocean Prediction Center.

![](media/image3.wmf){width="7.097222222222222in"
height="4.819444444444445in"}

> Number range CHAPTERFigure 3. Selected pressure observations and best
> track minimum central pressure curve for Subtropical Storm Andrea 9-11
> May 2007. Estimates during the extratropical stage are based partially
> on analyses from the Ocean Prediction Center.

![](media/image4.png){width="8.875in" height="5.429166666666666in"}

Number range CHAPTERFigure 4a. Vertical cross section of wind and
potential temperature obtained from dropwindsondes during Subtropical
Storm Andrea on 9 May between 1111-1202 UTC.

![](media/image5.png){width="8.504861111111111in"
height="5.565277777777778in"}

Figure 4b. GOES-East Satellite imagery at 1115 UTC 9 May indicating the
location of the dropwindsondes (X) in proximity to the storm center, the
drop id (6-digit number), and the time of the drop (4-digit number) in
coordinated universal time (UTC).

![](media/image6.png){width="8.6125in" height="5.626388888888889in"}

Figure 5. GOES-East Geostationary satellite imagery on 9 May at 1045 UTC
along with ocean surface vector winds from QuikSCAT (equally spaced wind
barbs), 1100 UTC metar surface data, 1100 UTC ship surface data, and
1200 UTC synoptic surface data.Number range CHAPTER