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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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