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Tropical Storm Wanda Discussion Number 16
NWS National Hurricane Center Miami FL AL212021
900 PM GMT Wed Nov 03 2021
Wanda's overall convective pattern has continued to improve since
the previous advisory with a curved convective band now wrapping
almost completely around the center, resulting in a 50-60-nmi wide
banded eye feature. However, the horizontal thickness of the
convective band has been waxing and waning, and cloud tops are only
around -50C to -55C. Satellite intensity estimates from TAFB and SAB
are a consensus T3.0/45 kt, while UW-CIMSS SATCON intensity
estimates range from 34 kt to 44 kt, respectively. Based on these
data, Wanda's intensity is being maintained at 45 kt. Although a
distinct eye feature is now evident, which would suggest a stronger
storm, a lower intensity is warranted since the cooler water beneath
the cyclone is likely creating a more stable boundary layer, which
is likely inhibiting the normal downward mixing of higher winds
aloft. This physical assumption is supported by weaker wind speeds
noted in earlier scatterometer surface wind data.
The initial motion estimate is a little east of due north, or 010/09
kt. There is no significant change to the previous forecast track
and rationale. An approaching mid-/upper-level trough from the west
should continue to lift Wanda northward for the next day or so,
followed by slowing and a sharp turn to the east by Thursday night
as the aforementioned trough weakens and lifts out to the north of
the cyclone. Subsequent ridging behind the trough will then force
Wanda southeastward to southward on Friday, followed by another
abrupt turn and acceleration to the northeast on Saturday as a
second and stronger deep-layer trough captures the cyclone. Despite
this complexity in the evolving steering pattern, the latest NHC
model guidance is in very agreement throughout the 120-h forecast
period on this track scenario. The new NHC forecast track is very
similar to the previous advisory track, and lies near or slightly
to the right of the tightly packed simple- and corrected-consensus
track models.
The improved inner-core convective structure argues for at least
some slight strengthening during the next couple of days despite
the expected 20-21-deg-C sea-surface temperatures (SST) beneath the
cyclone. Some cooling aloft associated with the aforementioned
second upper-level trough may help to offset the negative effects of
the relatively cool SSTs on day 3. In the 96-120-h period, Wanda is
expected to interact, and eventually merge, with a cold front
and become an extratropical low pressure system with gale-force
winds. The new official intensity forecast is very similar to the
previous advisory, and closely follows a blend of the intensity
consensus models IVCN, NOAA-HCCA, and Florida State FSSE.
FORECAST POSITIONS AND MAX WINDS
INIT 03/2100Z 39.8N 39.5W 45 KT 50 MPH
12H 04/0600Z 41.0N 39.4W 50 KT 60 MPH
24H 04/1800Z 41.9N 39.1W 50 KT 60 MPH
36H 05/0600Z 41.8N 38.0W 50 KT 60 MPH
48H 05/1800Z 40.3N 37.0W 50 KT 60 MPH
60H 06/0600Z 38.8N 36.9W 45 KT 50 MPH
72H 06/1800Z 38.1N 36.6W 45 KT 50 MPH
96H 07/1800Z 42.4N 31.5W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 08/1800Z 51.5N 19.2W 45 KT 50 MPH...POST-TROP/EXTRATROP
$$
Forecaster Stewart
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