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Tropical Storm Victor Forecast Discussion

WTNT45 KNHC 300842

Tropical Storm Victor Discussion Number   4
NWS National Hurricane Center Miami FL       AL202021
800 AM CVT Thu Sep 30 2021

Victor is gradually getting better organized.  AMSR2 microwave 
data from 0300 UTC showed that the low-level circulation has become 
more defined, with most convective banding features located west and
southwest of the center.  Victor's intensity is now estimated to be 
40 kt based on Dvorak estimates of T3.0 and T2.5 from TAFB and SAB, 
respectively, and objective numbers from UW-CIMSS around 40 kt.

Victor's vector is toward the west-northwest (290 degrees) at 11 
kt, and this heading should continue for the next 36 hours while 
the storm is located to the south a deep-layer ridge located over 
the subtropical eastern and central Atlantic.  In about 2 days, a 
mid- to upper-level low is forecast to develop over the central 
Atlantic, causing Victor to curve around the western periphery of 
the ridge, which gets shunted eastward between the Azores and the 
Canary Islands.  The track models are in generally good agreement 
on this scenario, and most of them are clustered tightly among each 
other.  Two notable exceptions, which are discounted at this time, 
are the HWRF and ECMWF models.  The HWRF, which is stronger than 
the other models, is way off to the east, while the ECMWF lies 
off to the south and west, a tendency that we've observed recently 
with other storms in the deep tropics.  The NHC track forecast is 
not changed much from the previous iteration and lies close to the 
GFS, HCCA, Florida State Superensemble, and TVCA solutions.

If the low-level circulation is in fact becoming better defined as 
shown by microwave imagery, Victor should be able to continue 
strengthening for the next couple of days in an environment of low 
vertical shear and over warm waters of roughly 28 degrees Celsius.  
The NHC intensity forecast is near the upper end of the guidance 
during this period and continues to show Victor reaching hurricane 
strength in about 36 hours.  Once the aforementioned mid- to 
upper-level low forms, strong southerly to southwesterly deep-layer 
shear is expected to develop over Victor and induce a weakening 
trend in about 3 days.  The intensity forecast has been lowered a 
bit during the latter part of the forecast period given the trends 
in the intensity models, but it is not as low as the HCCA and IVCN 
aids.  Interestingly, many of the global models suggest that the 
shear could be so strong that Victor might weaken to a depression 
or even degenerate into a remnant low by day 5.


INIT  30/0900Z  8.7N  27.3W   40 KT  45 MPH
 12H  30/1800Z  9.4N  28.8W   50 KT  60 MPH
 24H  01/0600Z 10.2N  30.6W   60 KT  70 MPH
 36H  01/1800Z 11.2N  32.3W   65 KT  75 MPH
 48H  02/0600Z 12.6N  33.8W   65 KT  75 MPH
 60H  02/1800Z 14.4N  35.3W   60 KT  70 MPH
 72H  03/0600Z 16.6N  37.0W   55 KT  65 MPH
 96H  04/0600Z 22.0N  40.2W   40 KT  45 MPH
120H  05/0600Z 27.3N  41.9W   35 KT  40 MPH

Forecaster Berg

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