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Subtropical Storm Leslie Discussion Number   5
NWS National Hurricane Center Miami FL       AL132018
1100 AM AST Mon Sep 24 2018

Conventional satellite imagery shows little change in Leslie's
cloud pattern during the past several hours with the exception of a
few new isolated thunderstorms developing near the surface center.
Accordingly, the initial intensity for this advisory is kept at 35
kt.  The statistical intensity guidance and the large-scale models
show Leslie commencing a strengthening trend in 24 hours as a
mid-latitude baroclinic system digs southeastward toward the
cyclone.  Some of the models also indicate that Leslie, after
completing an extratropical transition in around 48 hours, will
deepen and generate a large area of gale force winds, particularly
in the northwest quadrant.  The NHC intensity forecast reflects this
scenario and is just below the IVCN intensity consensus.

The initial motion is estimated to be an eastward drift, or 090/4 kt
within the increasing mid-level westerly steering flow.  A turn to
the east-northeast is forecast as an approaching mid-latitude
trough and associated cold front approaches from the northwest over
the central Atlantic.  The deterministic guidance indicate that the
aforementioned baroclinic system will overtake Leslie near the 48
hour period, and influence a transition to a non-tropical low
pressure system.  Subsequently, the GFS and the European models
still show extratropical Leslie as the primary system and deepening
with time.  For now, the official forecast will indicate a merging
scenario, but succeeding advisories may include extratropical low
forecast points through day 5.

FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 32.5N  48.0W   35 KT  40 MPH
 12H  25/0000Z 32.5N  47.2W   35 KT  40 MPH
 24H  25/1200Z 32.4N  45.5W   40 KT  45 MPH
 36H  26/0000Z 32.3N  42.8W   45 KT  50 MPH
 48H  26/1200Z 33.6N  39.9W   50 KT  60 MPH...POST-TROP/EXTRATROP
 72H  27/1200Z...MERGED WITH FRONT AND LARGER LOW

$$
Forecaster Roberts

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