Potential Tropical Cyclone Nine Forecast Discussion (Text)

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WTNT44 KNHC 171440

Potential Tropical Cyclone Nine Discussion Number   1
NWS National Hurricane Center Miami FL       AL092017
1100 AM AST Thu Aug 17 2017

Satellite imagery, including experimental 1-minute data from
GOES-16, indicates that the circulation of the low pressure area
east of the Lesser Antilles is becoming better defined, and that a
cluster of strong convection has formed just west of the center.
Based on this and the potential for the system to become a tropical
storm before reaching the Lesser Antilles, advisories are being
initiated as a potential tropical cyclone.  An Air Force Reserve
Hurricane Hunter aircraft is scheduled to investigate the system
this afternoon, and it is likely the aircraft will find a tropical
cyclone has formed.

The initial motion is 270/15.  A deep-layer ridge to the north of
the system should steer it generally just north of due west through
the forecast period, with this motion expected to bring the system
through the Lesser Antilles and into the eastern Caribbean Sea in
24-36 h, into the central Caribbean by 72 h, and to the western
Caribbean by 96-120 h.  The forecast track lies near the center of
the tightly clustered guidance envelope and lies near the various
consensus models.

The system is in an area of moderate easterly vertical shear, and
the large-scale models suggest that light/moderate shear should
continue through the forecast period.  This seems favorable for
strengthening, and the SHIPS and LGEM models show slow, but steady,
intensification.  However, the GFS and ECMWF models forecast the
system to degenerate to an easterly wave over the central Caribbean
Sea, possibly due to dry air entrainment.  The intensity forecast
follows the trend of the SHIPS/LGEM models, but it respects the
GFS/ECMWF forecasts by being on the low side of the intensity
guidance envelope.


INIT  17/1500Z 13.1N  54.1W   30 KT  35 MPH...POTENTIAL TROP CYCLONE
 12H  18/0000Z 13.1N  56.4W   30 KT  35 MPH...TROPICAL DEPRESSION
 24H  18/1200Z 13.2N  59.8W   35 KT  40 MPH
 36H  19/0000Z 13.5N  63.2W   40 KT  45 MPH
 48H  19/1200Z 13.9N  66.7W   45 KT  50 MPH
 72H  20/1200Z 14.5N  74.5W   55 KT  65 MPH
 96H  21/1200Z 15.5N  82.0W   65 KT  75 MPH
120H  22/1200Z 17.0N  87.5W   65 KT  75 MPH

Forecaster Beven

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Page last modified: Thursday, 17-Aug-2017 14:40:34 UTC