Atlantic Basin Tropical Cyclones

Tropical Storm Victor Forecast Discussion


000
WTNT45 KNHC 020245
TCDAT5

Tropical Storm Victor Discussion Number  11
NWS National Hurricane Center Miami FL       AL202021
1100 PM AST Fri Oct 01 2021

The structure of Victor this evening continues to degrade with the
low-level center becoming decoupled from the mid- to upper-level
circulation associated with the deeper convection. While the
tropical storm does continue to produce a region of deep convection
with cloud tops colder than -70 C, this activity is organized in a
linear band that is now more than 150 n mi northeast of the exposed
low-level center as seen on Proxy-Vis satellite imagery. Both
ASCAT-B/C clipped the western half of Victor's circulation, showing
peak winds of 40 kt on the far edge of the pass. In addition, the
latest subjective and objective satellite intensity estimates have
been falling this evening. The latest intensity for this advisory
has been lowered to 50 kt this advisory, assuming the scatterometer
data missed higher wind values to the northeast of Victor closer to
the convection. However, given Victor's current structure, this
estimate may still be generous.

Now that the low-level cloud swirl is readily apparent on satellite 
imagery, it is somewhat easier to track Victor this evening, with 
the estimated motion still west-northwest at 290/11 kt. Because the 
cyclone is also becoming more vertically shallow, the primarily 
steering feature will be a large low-level subtropical ridge 
centered to the north, which should guide Victor on a general 
west-northwestward to northwestward heading for the next 2-3 days at 
a similar forward motion. The latest track guidance has shifted 
westward this cycle, likely in response to Victor being a weaker 
cyclone less coupled to the deep convection. The latest NHC track 
forecast was also shifted a bit west over the forecast period, 
staying closer to the consensus aids HCCA and TVCA, though it is 
worth nothing this is still not as far west as the latest GFS or 
ECMWF runs.

While the deep-layer 200-850 hPa vertical wind shear has not been
prohibitively strong today (15-20 kt), more substantial mid-level
shear underneath the outflow layer (25-30 kt) appears to be
responsible for the current disheveled appearance of Victor. This
shear is related to a large upper-level cutoff low upstream of the
tropical storm. Even though the current shear is not expected to
increase much more in the short-term, the mid-level environment over
Victor is expected to continue drying as the existing shear will
import very dry air upstream into the core of the cyclone. All of
the guidance responds to these unfavorable conditions by gradually
weakening Victor over the next few days, and the latest NHC
intensity forecast has been lowered a bit more compared to the
previous advisory. While pulses of deep convection are likely to
continue north of Victor over the next several days, the circulation
is expected to gradually lose definition, and the global and
high-res regional hurricane models now open up the system into a
trough between 72-96 hours. The latest NHC intensity forecast now
follows suit, showing dissipation by 96 hours.


FORECAST POSITIONS AND MAX WINDS

INIT  02/0300Z 12.3N  35.3W   50 KT  60 MPH
 12H  02/1200Z 13.2N  36.9W   45 KT  50 MPH
 24H  03/0000Z 14.6N  38.7W   40 KT  45 MPH
 36H  03/1200Z 16.5N  40.6W   40 KT  45 MPH
 48H  04/0000Z 18.5N  42.6W   35 KT  40 MPH
 60H  04/1200Z 20.6N  44.7W   35 KT  40 MPH
 72H  05/0000Z 22.2N  46.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  06/0000Z...DISSIPATED

$$
Forecaster Papin



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