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Potential Tropical Cyclone SIX


Potential Tropical Cyclone Six Discussion Number   4
NWS National Hurricane Center Miami FL       AL062018
500 AM AST Fri Aug 31 2018

Even though the circulation is gradually becoming less elongated,
there is still relatively little deep convection near the estimated
center of circulation.  Instead, most of the convection remains
confined to the monsoon trough southwest of the center, where
low-level convergence is strongest.  Therefore, the system is not
quite yet being designated as a tropical cyclone.

Global model fields suggest that the low should detach from the
monsoon trough within the next 12 hours, which would likely allow
deep convection to form closer to the center.  Assuming that
happens, the system is also forecast to strengthen and become a
tropical storm by this afternoon while it approaches the southern
Cabo Verde Islands.  Although vertical shear is expected to be
relatively light for much of the forecast period, sea surface
temperatures ahead of the system are marginal, and the low will
likely move over a minimum of oceanic heat content in 48-72 hours.
Adding on top of that a drier mid-level environment, only gradual
strengthening is anticipated through day 5.  A majority of the
intensity models agree on this scenario, with the exception of the
HWRF model, which brings the system close to major hurricane
strength at the end of the forecast period.  Since that solution is
discounted at the moment, the NHC intensity forecast is below the
HCCA guidance and closest to the intensity consensus.

The low appears to have turned west-northwestward with an initial
motion of 285/10 kt.  A mid-level high centered west of the Canary
Islands should continue to steer the disturbance west-northwestward
at a faster clip for the next 4 days or so.  By the end of the
forecast period, a weakness in the ridge over the eastern Atlantic
could cause the system to turn northwestward.  The new NHC track
forecast is a little slower than the previous one during the first
72 hours and then a little to the west on days 4 and 5 to better
match the latest guidance envelope.


INIT  31/0900Z 13.6N  21.4W   30 KT  35 MPH...POTENTIAL TROP CYCLONE
 12H  31/1800Z 14.2N  23.1W   35 KT  40 MPH...TROPICAL STORM
 24H  01/0600Z 14.8N  25.6W   40 KT  45 MPH
 36H  01/1800Z 15.5N  28.3W   45 KT  50 MPH
 48H  02/0600Z 16.2N  30.9W   50 KT  60 MPH
 72H  03/0600Z 17.4N  36.2W   55 KT  65 MPH
 96H  04/0600Z 19.0N  41.0W   60 KT  70 MPH
120H  05/0600Z 21.5N  45.0W   65 KT  75 MPH

Forecaster Berg