Noel was a 65-knot
hurricane
that remained at sea over the eastern Atlantic.
a. Synoptic History
Satellite pictures and rawinsonde data show that a
tropical wave
emerged from western Africa on 22 September. Three days
later, as the wave neared 30°W longitude, bands of deep convection
associated with the system began to acquire some cyclonic shape and the NHC's
Tropical Analysis and Forecast Branch (TAFB)
meteorologist gave the first location estimate at 0600 UTC 26
September, remarking "potential surface low looking like it's
getting more organized". Twenty-four hours later, TAFB
and the Synoptic Analysis Branch
(SAB) gave the initial Dvorak
classifications. By 1800 UTC on the 26th, the cloud structure was
strongly indicative of a low-level circulation and the post-analysis
"best track"
of Tropical Depression
Sixteen begins at this time (Table 1 and
Fig. 1 [57K GIF]) over the eastern tropical Atlantic.
A mid- to upper-tropospheric trough lay in the path of the
developing tropical cyclone.
Southwesterly shearing due to the upper-level winds ahead of this trough started to
affect the depression as early as 27 September. However, these winds were not
strong enough to totally offset the development trend and the
depression strengthened into Tropical Storm
Noel around 1200 UTC on the 27th.
As the cyclone strengthened into a storm, its motion turned
from west-northwestward to northwestward, due the influence of the
above trough and an accompanying mid- to upper-level low near 28°N
44°W. A northwestward movement continued until about 1800 UTC on
the 28th, when Noel began to take a more northerly heading. Even
though upper-level outflow was being impeded to the northwest,
satellite intensity estimates indicate that Noel strengthened to a
hurricane near 1800 UTC 28 September.
Development was halted after that juncture by increasing upper-level southwesterly flow. Moving
northward to northeastward, Noel maintained minimal hurricane strength until 30 September,
when the center
became exposed to the southwest of the cluster of convection associated with the cyclone.
Gradual weakening took place, and the forward speed slowed to a
crawl on 30 September and 1 October. On 2 October, with its
maximum winds reduced to 45 knots, Noel moved generally
northward at a faster speed. On the 3rd, the steering of Noel was influenced
by a mid- to upper-level cyclone centered just to the west, and the
storm moved north-northwestward for a while.
Shearing diminished as Noel came into the area of lighter
upper-level winds near the center of the mid- to upper-level
cyclone, and this allowed the storm to re-strengthen on the 3rd and
4th. By 0000 UTC 5 October, Noel was again a 65-knot
hurricane. The system maintained this intensity for about 24 hours while
moving slowly northeastward to eastward. The final weakening
commenced at 0000 UTC on the 6th, when Noel's winds dropped to just
below hurricane strength. A midlatitude trough approached the
area, causing Noel to move more rapidly, toward the east-northeast
and northeast. Gradually weakening and losing its tropical
character as it approached the Azores, the cyclone was absorbed
into a cold front near 0000 UTC 8 October.
b. Meteorological Statistics
The post-analysis best track intensities are listed in
Table 1 and displayed in
Figs. 2 and 3 (59K GIF),
which show the estimated minimum central pressure and maximum one-minute wind speed,
respectively, versus time. These intensity estimates were derived mainly from
analyses of satellite images, using the Dvorak technique, performed
by meteorologists at the SAB and TAFB
(formerly the Tropical Satellite Analysis and Forecast unit, TSAF, as in the figures) and
at the Air Force Global Weather Central (AFGWC).
In addition, there were some surface observations from ships of opportunity
which were used for the intensity estimates. An observation of 65-knot
winds from the ship FNOU was instrumental in re-upgrading Noel
to a hurricane at 0000 UTC 5 October. Table 2 is a listing of ship
reports of tropical storm force or higher wind speeds associated with Noel.
c. Casualty and Damage Statistics
Noel did not significantly affect any land areas, and there
are no reports of casualties or damage.
d. Forecast and Warning Critique
In general, the track of Noel was reasonably well predicted.
At 12, 24, 36, 48, and 72 hours the respective mean official
forecast errors were 47, 93, 138, 178, and 229 n mi. These are
below the most recent 10-year average errors. Compared to the
official forecast, there was no available objective technique which
had a lower average error for any of the forecast times.
For the most part, the intensity of Noel was somewhat
underpredicted. This was especially true for the restrengthening
phase, where there were several 72-hours wind forecasts that were
35 knots too low.
Since this cyclone remained at sea, no watches or warnings
were required.
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