Tropical Cyclone Report

Hurricane Cosme

(EP062007)

14 -- 22 July 2007

Michelle Mainelli

National Hurricane Center

17 December 2007

This report was corrected on 17 December 2007 to modify the best track
for 1800 UTC 22 July when the system was a remnant low.

Cosme was briefly a category 1 hurricane on the Saffir-Simpson Hurricane
Scale that remained over the open waters of the eastern and central
North Pacific.

a.  Synoptic History

    Cosme originated from a tropical wave that emerged off the coast of
    Africa on 27 June. The wave was difficult to track across the
    Atlantic Ocean and Caribbean Sea due to a lack of convective
    activity, but is estimated to have entered into the eastern North
    Pacific basin around 8 July. The wave began to show signs of
    organization on 10 July, but remained embedded within the
    InterTropical Convergence Zone (ITCZ) for the next couple of days
    and was slow to develop a well-defined circulation. After separating
    from the ITCZ on 13 July, the system gradually gained convective
    organization and became a tropical depression by 1200 UTC 14 July,
    centered about 1725 n mi east-southeast of Hilo, Hawaii. 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 had a very large circulation and initially moved
    slowly toward the northwest in response to a weakness in a high
    pressure ridge to the north. Once convection deepened and a
    well-defined banding feature developed on July 15, the cyclone
    became a tropical storm at 1800 UTC that same day. With both the
    atmospheric and oceanic environments conducive for strengthening
    (low vertical shear and warm waters), Cosme reached hurricane
    strength 24 hours later while centered about 1400 n mi east of Hilo.
    At this time, both conventional and passive microwave satellite
    imagery showed hints of a developing eye feature. The strengthening
    episode was short-lived, however, and Cosme only maintained
    hurricane status for six hours as a result of cooler waters.

    Cosme was now being steered toward the west as the ridge to the
    north had strengthened. By early on 17 July, the cyclone reached an
    environment of moderate easterly shear and 25^o^C waters, and Cosme
    weakened to a tropical storm. The cyclone continued to slowly weaken
    as it moved westward and became a tropical depression at 1800 UTC 18
    July, about 900 n mi east-southeast of Hilo. The depression
    continued westward and crossed 140^o^W into the central North
    Pacific basin around 0000 UTC 19 July, where it became the forecast
    responsibility of the Central Pacific Hurricane Center. The
    depression continued westward for the next four days and remained
    well to the south of the Hawaiian Islands. The cyclone degenerated
    to a remnant low late on 22 July, about 180 n mi east-southeast of
    Johnston Island, and the low dissipated by 1800 UTC 24 July, about
    570 n mi west of Johnston Island.

b.  Meteorological Statistics

    Observations in Cosme (Figs. 2 and 3) include satellite-based Dvorak
    technique intensity estimates from the Tropical Analysis and
    Forecast Branch (TAFB) and the Satellite Analysis Branch (SAB).
    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 Cosme. Analysis from a 1435 UTC QuikSCAT
    pass on 16 July yielded a peak intensity of at least 60 kt, and by
    1800 UTC Dvorak satellite intensity estimates from both TAFB and SAB
    supported hurricane strength as an eye feature became apparent and
    the satellite appearance became better defined.

    No ship or land station reported sustained winds of at least
    tropical storm force in association with Cosme.

c.  Casualty and Damage Statistics

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

d.  Forecast and Warning Critique

    The potential development of Cosme was first introduced into the
    Tropical Weather Outlook (TWO) on 10 July, about four days prior to
    genesis. The system was described as an area of disturbed weather
    located about 700 miles south of the southern tip of Baja California
    with additional development possible over the next couple of days.
    By late on 11 July, however, the system became indistinct within the
    ITCZ and the potential for further development appeared to have
    lessened. Subsequently the system was removed from the TWO but was
    reintroduced early on 13 July for the possibility of slow
    development. During the morning of 14 July, visible imagery
    indicated that the area of disturbed weather had developed a surface
    circulation and enough deep convection to be classified as a
    tropical depression. Despite the inclusion of the system in the TWO,
    no explicit mention of tropical depression formation was ever made.

    A verification of NHC official and guidance model track forecasts is
    given in Table 2. Average official track errors for Cosme were 33,
    50, 64, 75, 102, 155, and 232 n mi for the 12, 24, 36, 48, 72, 96,
    and 120 h forecasts, respectively, which there were 18 forecasts
    made for each period out through 72 hours. These errors are lower
    than or close to the average long-term official track errors for all
    forecast periods (Table 2). The consensus models (GUNA/FSSE) and the
    GFSI and AEMI models performed quite well and had lower errors than
    the official forecasts through 48 h. In particular, the FSSE had the
    lowest track errors of all the model guidance at all forecast lead
    times through 96 h. With the exception of the GFDI and FSSE track
    forecasts, the 120 h track errors from the model guidance were
    rather large, between 250 n mi and 500 n mi, as most models
    predicted Cosme to remain a stronger cyclone and be steered toward
    the west-northwest.

    Average NHC official intensity errors were 6, 9, 11, 10, 8, 8, and 4
    kt for the 12, 24, 36, 48, 72, 96, and 120 h forecasts, respectively
    (Table 3). For comparison, the average long-term official intensity
    errors are 6, 11, 15, 17, 19, 19, and 19 kt, respectively. The
    official intensity forecast errors were better than the average
    long-term errors at all forecast periods. Notably, the official
    intensity forecast errors were much lower than the long-term average
    errors at 48, 72, 96, and 120 h. These low errors are attributed to
    official intensity forecasts that accurately predicted Cosme to
    weaken in the later forecasts due to the cyclone encountering cooler
    waters and increased vertical wind shear. The ICON consensus (GHMI
    and DSHP) performed well and was slightly better than the official
    forecasts for Cosme at forecast periods 36 h through 96 h.

    Table 1. Best track for Hurricane Cosme, 14 -- 22 July, 2007. Best
    track information west of 140^o^W was provided by the Central
    Pacific Hurricane Center.

+-------------+-------+---------+---------+----------+----------------+
| Date/Time   | Lat   | Lo      | P       | Wind     | Stage          |
|             | itude | ngitude | ressure | Speed    |                |
| (UTC)       |       |         |         |          |                |
|             | \(N\) | \(W\)   | (mb)    | (kt)     |                |
+-------------+-------+---------+---------+----------+----------------+
| 14 / 1200   | 11.2  | 125.8   | 1007    | 25       | tropical       |
|             |       |         |         |          | depression     |
+-------------+-------+---------+---------+----------+----------------+
| 14 / 1800   | 11.3  | 126.3   | 1007    | 25       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 15 / 0000   | 11.6  | 126.6   | 1006    | 25       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 15 / 0600   | 11.9  | 126.9   | 1006    | 25       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 15 / 1200   | 12.1  | 127.2   | 1006    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 15 / 1800   | 12.5  | 127.7   | 1005    | 35       | tropical storm |
+-------------+-------+---------+---------+----------+----------------+
| 16 / 0000   | 13.0  | 128.4   | 1000    | 45       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 16 / 0600   | 13.6  | 129.1   | 997     | 55       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 16 / 1200   | 14.0  | 130.0   | 992     | 60       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 16 / 1800   | 14.4  | 130.9   | 987     | 65       | hurricane      |
+-------------+-------+---------+---------+----------+----------------+
| 17 / 0000   | 14.8  | 131.8   | 992     | 60       | tropical storm |
+-------------+-------+---------+---------+----------+----------------+
| 17 / 0600   | 14.9  | 132.8   | 997     | 55       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 17 / 1200   | 14.9  | 133.8   | 1000    | 45       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 17 / 1800   | 14.9  | 134.8   | 1005    | 35       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 18 / 0000   | 15.0  | 136.0   | 1005    | 35       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 18 / 0600   | 15.1  | 137.2   | 1005    | 35       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 18 / 1200   | 15.1  | 138.3   | 1005    | 35       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 18 / 1800   | 15.0  | 139.5   | 1006    | 30       | tropical       |
|             |       |         |         |          | depression     |
+-------------+-------+---------+---------+----------+----------------+
| 19 / 0000   | 15.2  | 140.7   | 1008    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 19 / 0600   | 15.3  | 142.0   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 19 / 1200   | 15.5  | 143.6   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 19 / 1800   | 15.7  | 145.0   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 20 / 0000   | 16.0  | 146.6   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 20 / 0600   | 16.0  | 148.3   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 20 / 1200   | 16.1  | 149.9   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 20 / 1800   | 16.5  | 151.8   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 21 / 0000   | 16.5  | 153.8   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 21 / 0600   | 16.3  | 155.7   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 21 / 1200   | 16.1  | 157.4   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 21 / 1800   | 16.2  | 159.1   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 22 / 0000   | 16.4  | 161.0   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 22 / 0600   | 16.4  | 162.6   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 22 / 1200   | 16.3  | 164.5   | 1010    | 30       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 22 / 1800   | 16.1  | 166.5   | 1010    | 25       | remnant low    |
+-------------+-------+---------+---------+----------+----------------+
| 23 / 0000   | 16.1  | 168.3   | 1011    | 25       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 23 / 0600   | 15.9  | 170.0   | 1011    | 25       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 23 / 1200   | 15.8  | 171.7   | 1011    | 25       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 23 / 1800   | 15.7  | 173.3   | 1011    | 25       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 24 / 0000   | 15.7  | 175.0   | 1011    | 25       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 24 / 0600   | 15.7  | 176.8   | 1011    | 25       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 24 / 1200   | 15.8  | 178.3   | 1010    | 25       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 24 / 1800   | 15.8  | 179.4   | 1009    | 25       | \"             |
+-------------+-------+---------+---------+----------+----------------+
| 25 / 0000   |       |         |         |          | dissipated     |
+-------------+-------+---------+---------+----------+----------------+
| 16 / 1800   | 14.4  | 130.9   | 987     | 65       | minimum        |
|             |       |         |         |          | pressure       |
+-------------+-------+---------+---------+----------+----------------+

Table 2. Preliminary track forecast evaluation (heterogeneous sample)
for Hurricane Cosme, 14 -- 22 July 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.

+-----------+-------+-------+-------+-------+-------+-------+-------+
| Forecast  | For   |       |       |       |       |       |       |
| Technique | ecast |       |       |       |       |       |       |
|           | P     |       |       |       |       |       |       |
|           | eriod |       |       |       |       |       |       |
|           | (h)   |       |       |       |       |       |       |
+===========+=======+=======+=======+=======+=======+=======+=======+
|           | 12    | 24    | 36    | 48    | 72    | 96    | 120   |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CLP5      | 42    | 83    | 122   | 163   | 265   | 380   | 503   |
|           | (18)  | (18)  | (18)  | (18)  | (18)  | (17)  | (13)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFNI      | **32  | 54    | 77    | 106   | 162   | 279 ( | 457 ( |
|           | (     | (11)  | (11)  | (11)  | (10)  | 7)    | 6)    |
|           | 11)** |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFDI      | **26  | **42  | 64    | 85    | 138   | 187   | **221 |
|           | (     | (     | (16)  | (16)  | (16)  | (15)  | (     |
|           | 16)** | 16)** |       |       |       |       | 11)** |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GFSI      | **21  | **28  | **38  | **50  | 104   | 184   | 258   |
|           | (     | (     | (     | (     | (17)  | (16)  | (12)  |
|           | 17)** | 17)** | 17)** | 17)** |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| AEMI      | **27  | **35  | **47  | **65  | 110   | 176   | 339 ( |
|           | (     | (     | (     | (     | (17)  | (15)  | 7)    |
|           | 17)** | 17)** | 17)** | 17)** |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NGPI      | **22  | **46  | 72    | 102   | 161   | 240   | 421 ( |
|           | (     | (     | (11)  | (11)  | (11)  | (10)  | 5)    |
|           | 11)** | 11)** |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| UKMI      | **28  | 53    | 81    | 118   | 225   | 340 ( | 415 ( |
|           | (     | (10)  | (10)  | (10)  | (10)  | 9)    | 5)    |
|           | 10)** |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMD      | 40    | 66    | 87    | 112   | 184   | 272   | 357   |
|           | (18)  | (18)  | (18)  | (18)  | (18)  | (17)  | (13)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMM      | 42    | 71    | 95    | 122   | 184   | 243   | 303   |
|           | (18)  | (18)  | (18)  | (18)  | (18)  | (17)  | (13)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| BAMS      | 48    | 81    | 108   | 131   | 189   | 240   | 302   |
|           | (16)  | (16)  | (16)  | (16)  | (16)  | (15)  | (13)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| CONU      | **24  | **37  | **56  | 77    | 129   | 180   | 256   |
|           | (     | (     | (     | (16)  | (16)  | (15)  | (11)  |
|           | 16)** | 16)** | 16)** |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| GUNA      | **18  | **35  | **51  | **73  | 140   | 219   | 288 ( |
|           | (     | (     | (     | (     | (11)  | (10)  | 5)    |
|           | 11)** | 11)** | 11)** | 11)** |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| FSSE      | **15  | **27  | **44  | **54  | **83  | **115 | 249 ( |
|           | (     | (     | (     | (     | (     | (     | 5)    |
|           | 13)** | 13)** | 8)**  | 7)**  | 7)**  | 6)**  |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| OFCL      | 33    | 50    | 64    | 75    | 102   | 155   | 232   |
|           | (18)  | (18)  | (18)  | (18)  | (18)  | (17)  | (13)  |
+-----------+-------+-------+-------+-------+-------+-------+-------+
| NHC       | 33    | 57    | 79    | 99    | 140   | 188   | 233   |
| Official  |       |       |       |       |       |       |       |
|           | \(1   | \(1   | \(1   | \(    | \(    | \(    | \(    |
| (         | 349\) | 192\) | 039\) | 897\) | 655\) | 465\) | 311\) |
| 2002-2006 |       |       |       |       |       |       |       |
| mean)     |       |       |       |       |       |       |       |
+-----------+-------+-------+-------+-------+-------+-------+-------+

Table 3. Preliminary intensity forecast evaluation (heterogeneous
sample) for Hurricane Cosme, 14 -- 22 July 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.

+----------+-------+--------+-------+--------+-------+-------+-------+
| Forecast | For   |        |       |        |       |       |       |
| T        | ecast |        |       |        |       |       |       |
| echnique | P     |        |       |        |       |       |       |
|          | eriod |        |       |        |       |       |       |
|          | (h)   |        |       |        |       |       |       |
+==========+=======+========+=======+========+=======+=======+=======+
|          | 12    | 24     | 36    | 48     | 72    | 96    | 120   |
+----------+-------+--------+-------+--------+-------+-------+-------+
| SHF5     | 7.4   | 12.2   | 14.8  | 15.1   | 16.6  | 17.2  | 19.6  |
|          | (18)  | (18)   | (18)  | (18)   | (18)  | (17)  | (13)  |
+----------+-------+--------+-------+--------+-------+-------+-------+
| GFDI     | 9.1   | 10.7   | *     | **9.9  | 9.6   | 10.3  | 14.4  |
|          | (16)  | (16)   | *10.3 | (16)** | (16)  | (15)  | (11)  |
|          |       |        | (     |        |       |       |       |
|          |       |        | 16)** |        |       |       |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| SHIP     | 6.7   | 10.2   | *     | 10.7   | 11.6  | 9.6   | 8.3   |
|          | (18)  | (18)   | *11.2 | (16)   | (16)  | (16)  | (13)  |
|          |       |        | (     |        |       |       |       |
|          |       |        | 18)** |        |       |       |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| DSHP     | 6.7   | 10.2   | *     | 10.7   | 11.6  | 9.3   | 8.1   |
|          | (18)  | (18)   | *11.2 | (16)   | (16)  | (15)  | (12)  |
|          |       |        | (     |        |       |       |       |
|          |       |        | 18)** |        |       |       |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| FSSE     | 7.7   | 9.8    | 15.6  | 17.6   | 15.6  | 8.8   | **3.6 |
|          | (13)  | (13)   | (8)   | (7)    | (7)   | (6)   | (5)** |
+----------+-------+--------+-------+--------+-------+-------+-------+
| ICON     | 7.4   | 8.9    | **9.8 | **8.1  | **7.9 | **8.1 | 9.3   |
|          | (16)  | (16)   | (     | (16)** | (     | (     | (11)  |
|          |       |        | 16)** |        | 16)** | 15)** |       |
+----------+-------+--------+-------+--------+-------+-------+-------+
| OFCL     | 6.4   | 8.9    | 11.4  | 10.3   | 8.3   | 8.2   | 4.2   |
|          | (18)  | (18)   | (18)  | (18)   | (18)  | (17)  | (13)  |
+----------+-------+--------+-------+--------+-------+-------+-------+
| NHC      | 6.3   | 11.0   | 14.6  | 16.9   | 18.9  | 18.5  | 19.3  |
| Official |       |        |       |        |       |       |       |
|          | \(1   | \(     | \(1   | \      | \(    | \(    | \(    |
| (2       | 349\) | 1192\) | 039\) | (896\) | 655\) | 465\) | 311\) |
| 002-2006 |       |        |       |        |       |       |       |
| mean)    |       |        |       |        |       |       |       |
+----------+-------+--------+-------+--------+-------+-------+-------+

Figure 1. Best track positions for Cosme, 14 -- 22 July 2007. Best track
information west of 140^o^W was provided by the Central Pacific
Hurricane Center.

![](media/image1.wmf){width="7.370138888888889in"
height="6.090972222222222in"}

Figure 2. Selected wind observations and best track maximum sustained
surface wind speed

curve for Cosme, 14 -- 22 July 2007. The best track maximum sustained
surface wind speed after 1800 UTC 18 July was provided by the Central
Pacific Hurricane Center.

![](media/image2.wmf){width="6.749305555555556in"
height="4.582638888888889in"}

Figure 3. Selected pressure observations and best track minimum central
pressure curve for Cosme, 14 -- 22 July 2007. The best track minimum
central pressure after 1800 UTC 18 July was provided by the Central
Pacific Hurricane Center.

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