Atlantic Basin Tropical Cyclones

Subtropical Storm Wanda Forecast Discussion


479 
WTNT41 KNHC 310841
TCDAT1

Subtropical Storm Wanda Discussion Number   2
NWS National Hurricane Center Miami FL       AL212021
900 AM GMT Sun Oct 31 2021

Satellite imagery indicates that the convection associated with 
Wanda has become better organized since the last advisory, with a 
convective band now wrapping more than halfway around the center.  
However, the cyclone remains embedded in a deep-layer baroclinic 
circulation, and based on this structure, the system is still a 
subtropical storm.  Satellite intensity estimates are in the 40-50 
kt range, and the intensity is set at a possibly conservative 45 kt.

The initial motion is a little slower toward the east-southeast at 
105/14 kt.  As mentioned in the previous advisory, a slower 
east-southeast to southeast motion is expected during the next day 
or so as Wanda moves with the deep-layer trough that it is embedded 
within.  After that time, the trough is expected to cut off, and 
Wanda will likely meander on Monday before turning sharply northward 
or northeastward by the middle of next week when the system moves in 
the flow between the cut off low and a building ridge.  By the end 
of the forecast period, the cyclone is expected to turn 
northeastward in southwesterly mid-latitude flow.  The new track 
guidance is similar to the previous guidance, but is a little slower 
after 72 h. Thus, the new forecast track is similar to the previous 
track and also slower in the later periods.

Given the increasing organization, it is likely that Wanda will 
strengthen some during the next 24 h.  After that, the intensity 
guidance suggests little change in strength through 48 h as the 
cyclone moves over sea surface temperatures of 24 C.  Beyond 48 h, 
gradual weakening is expected as Wanda moves over colder waters, 
with the system expected to become post-tropical due to a lack of 
convection by 120 h.  It should be noted that the GFS and UKMET 
suggest the possibility that Wanda could transition into a tropical 
storm by 48 h.  However, due to the expectation that the cyclone 
will continue to remain embedded in a cold upper-level trough, the 
intensity forecast will not explicitly call for tropical transition 
at this time.


FORECAST POSITIONS AND MAX WINDS

INIT  31/0900Z 36.5N  43.9W   45 KT  50 MPH
 12H  31/1800Z 36.2N  43.0W   50 KT  60 MPH
 24H  01/0600Z 35.3N  42.8W   50 KT  60 MPH
 36H  01/1800Z 34.6N  42.0W   50 KT  60 MPH
 48H  02/0600Z 34.8N  40.7W   50 KT  60 MPH
 60H  02/1800Z 36.2N  39.6W   50 KT  60 MPH
 72H  03/0600Z 38.3N  39.0W   45 KT  50 MPH
 96H  04/0600Z 43.0N  38.0W   45 KT  50 MPH
120H  05/0600Z 47.0N  32.5W   40 KT  45 MPH...POST-TROPICAL

$$
Forecaster Beven




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