Atlantic Basin Tropical Cyclones

Subtropical Storm Wanda Forecast Discussion


000
WTNT41 KNHC 011445
TCDAT1

Subtropical Storm Wanda Discussion Number   7
NWS National Hurricane Center Miami FL       AL212021
300 PM GMT Mon Nov 01 2021

Wanda has been moving southeastward since the previous advisory and 
has now moved back underneath the axis of the upper-level trough 
that the cyclone is embedded in. However, strong northwesterly 
vertical wind shear of 30-35 kt has persisted and has displaced the 
deep convection into the southeastern quadrant. The initial 
intensity has been lowered to 40 kt based on a blend of satellite 
intensity estimates of 35 kt from TAFB, and 39 kt and 41 kt from 
UW-CIMSS ADT and SATCON, respectively.

Although Wanda had been moving southeastward at 10-11 kt as of 1200 
UTC, the most recent motion vector appears to be slowly eastward or 
090/05 kt. Wanda and the parent upper-level trough should move 
eastward this late morning and early afternoon, and then turn 
northeastward by this evening, followed by a northward motion by 
late Tuesday as southerly steering flow gradually develops between a 
larger mid-latitude trough to the west and a ridge to the east. By 
day 3, another mid-latitude ridge is forecast to build between Wanda 
and the aforementioned larger trough, causing the cyclone to turn 
eastward and then southward toward the westernmost Azores.  The 
latest NHC track guidance has shifted sharply to the east of the 
previous forecast track through 72 hours, and the new official track 
forecast has followed suit. However, the new advisory track lies 
along the western edge of the guidance through day 3, and then lies 
in the middle of the track guidance envelope on days 4 and 5.

Although Wanda has weakened slightly, some slight restrengthening 
will be possible in the 24-60-h period when the shear is forecast to 
decrease sharply down to around 10 kt while the cyclone remains over 
23.5-24-deg-C sea-surface temperatures. The weaker shear conditions 
should also help Wanda transition to a tropical cyclone. By 96 h, 
however, Wanda is forecast to devolve into a post-tropical low due 
to the cyclone moving over sub-20-deg-C water temperatures, into a 
significantly drier air mass, and into strong southerly vertical 
wind shear -- a detrimental combination that should cause the 
convection to erode near the center.  The new NHC intensity forecast 
is essentially unchanged from the previous advisory.


FORECAST POSITIONS AND MAX WINDS

INIT  01/1500Z 34.0N  43.0W   40 KT  45 MPH
 12H  02/0000Z 34.1N  42.0W   40 KT  45 MPH
 24H  02/1200Z 35.0N  41.1W   45 KT  50 MPH...TROPICAL CYCLONE
 36H  03/0000Z 36.8N  40.2W   45 KT  50 MPH
 48H  03/1200Z 39.0N  40.0W   45 KT  50 MPH
 60H  04/0000Z 40.8N  39.7W   45 KT  50 MPH
 72H  04/1200Z 42.3N  39.0W   45 KT  50 MPH
 96H  05/1200Z 43.6N  34.0W   45 KT  50 MPH...POST-TROPICAL
120H  06/1200Z 42.9N  31.5W   40 KT  45 MPH...POST-TROPICAL

$$
Forecaster Stewart



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