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Potential Tropical Cyclone Eighteen Discussion Number   1
NWS National Hurricane Center Miami FL       AL182017
500 PM EDT Fri Oct 27 2017

Data from an Air Force Reserve Hurricane Hunter aircraft
investigating the disturbance over the northwestern Caribbean Sea
indicate that the system does not yet have a well-defined center. In
fact, the aircraft data and satellite imagery suggest that there are
multiple circulations embedded within a broader circulation at this
time. Given the lack of a well-defined center, the system is not a
tropical cyclone, but since tropical storm conditions are expected
to affect Cuba and the northwestern Bahamas in the next 24 to 36
hours, advisories are being initiated on the system as a potential
tropical cyclone at this time.

The initial intensity is set to 35 kt based on aircraft data, with
these winds found well south of the broad circulation center.
However, NOAA buoy 42057 also reported a peak 1-minute wind of 31 kt
earlier today. Aircraft data suggest that the central pressure is
around 1006 mb. The system is situated in a low-shear environment
and over warm waters, so some slow strengthening is expected in the
first 24 hours before the system reaches Cuba. The official forecast
follows the trend of the intensity consensus in showing a peak of
around 45 kt at 36 and 48 hours before the system is absorbed by an
approaching cold front in 60-72 hours.

Given the lack of a well-defined center, the initial position is and
the initial motion of 330/05 are highly uncertain. A faster
northward motion should begin soon as the disturbance begins to
recurve ahead of an approaching mid/upper-level trough moving into
the southeastern United States. This trough should cause a faster
northeastward acceleration at 24 through 48 hours. The track model
guidance is in generally good agreement on the overall scenario,
with more along than cross track spread. The NHC forecast leans
toward a blend of the ECMWF and GFS models and is a little slower
than the current multi-model consensus. Not surprisingly, given the
disorganized initial state of the system, the track forecast
uncertainty is larger than usual.

FORECAST POSITIONS AND MAX WINDS

INIT  27/2100Z 17.5N  84.5W   35 KT  40 MPH...POTENTIAL TROP CYCLONE
 12H  28/0600Z 19.1N  84.1W   35 KT  40 MPH...TROPICAL STORM
 24H  28/1800Z 21.7N  82.4W   40 KT  45 MPH
 36H  29/0600Z 24.6N  79.6W   45 KT  50 MPH
 48H  29/1800Z 28.0N  75.5W   45 KT  50 MPH
 72H  30/1800Z...ABSORBED

$$
Forecaster Brennan

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