[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 071449
TCDAT3

Tropical Storm Leslie Discussion Number  45
NWS National Hurricane Center Miami FL       AL132018
1100 AM AST Sun Oct 07 2018

Despite marginal SSTs near 24 deg C, Leslie has persisted with
little change in its structure. An average of the UW-CIMSS SATCON
and current intensity estimates from TAFB and SAB still supports an
initial intensity of 50 kt. Although Leslie is currently located in
a low-shear environment, GFS and ECMWF SHIPS diagnostics suggests
that mid-level humidities are fairly low, and the cyclone should
remain over marginal SSTs for the foreseeable future.  All of the
intensity guidance forecasts little to no intensity change during
the next day or so.  However, by 36 h, nearly all of the dynamical
models, both global and regional, forecast that Leslie will begin to
restrengthen.  On the other hand, the statistical-dynamical models
do not forecast much change through day 5.  The NHC forecast has
been adjusted a little higher to keep it close to the intensity
consensus, and I can't rule out that Leslie could become a hurricane
again at some point during the coming week.

No large changes were made to the NHC track forecast, but this
should not be interpreted as a sign of confidence in the forecast.
Leslie is currently moving with an initial motion of east-southeast,
or 115/9 kt. The track model spread is high from the very beginning
of the forecast, with the GFS and its associated regional models
indicating that Leslie will continue on a similar heading for the
next several days, while the ECMWF and UKMET forecast that Leslie
will slow down and turn soon turn toward the southeast or
south-southeast. The track forecast variance stems from differences
in how quickly the models show Leslie separating from a mid-level
trough to its north, if at all, and by day 5, the GFS and ECMWF
solutions vary by about 750 n mi. At this point, I don't have a good
reason to pick one solution over another, and it should be noted
that based on the ECMWF ensemble tracks, there is a whole spectrum
of possible solutions between these extremes. The NHC track forecast
therefore remains near the TVCN and GFEX aids as a course of least
regret, but significant changes could be required to future
advisories if the track of Leslie becomes more clear.

Large swells generated by Leslie are expected to continue through
tonight across the northeastern coast of the United States, Bermuda,
the Greater and Lesser Antilles, and Atlantic Canada. Please
consult products from your local weather office as these conditions
could cause life-threatening surf and rip currents.


FORECAST POSITIONS AND MAX WINDS

INIT  07/1500Z 36.6N  51.4W   50 KT  60 MPH
 12H  08/0000Z 36.2N  49.7W   50 KT  60 MPH
 24H  08/1200Z 35.4N  47.3W   50 KT  60 MPH
 36H  09/0000Z 34.2N  44.5W   55 KT  65 MPH
 48H  09/1200Z 32.6N  41.7W   55 KT  65 MPH
 72H  10/1200Z 29.1N  36.6W   60 KT  70 MPH
 96H  11/1200Z 28.5N  31.9W   60 KT  70 MPH
120H  12/1200Z 30.0N  28.0W   55 KT  65 MPH

$$
Forecaster Zelinsky
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