[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 121438
TCDAT3

Hurricane Leslie Discussion Number  65
NWS National Hurricane Center Miami FL       AL132018
1100 AM AST Fri Oct 12 2018

Leslie's cloud pattern continues to feature a central dense
overcast, but with only hints of an eye in visible imagery. A
partial northern eyewall was noted on a 0910Z SSMIS overpass. Dvorak
intensity estimates have decreased slightly, and based on this, the
initial intensity has been conservatively nudged down to 75 kt. The
wind field is quite large, especially south of the center, as
confirmed by a pair of recent ASCAT passes, and the initial wind
radii have been adjusted using those data.

The initial motion estimate is now 070/28. Leslie is moving quickly
east-northeastward on the southern side of a powerful longwave
trough centered over the north Atlantic. The track forecast
reasoning has changed since the last advisory, with the GFS, ECMWF,
and now the 06Z run of the UKMET all showing a more eastward motion
of Leslie toward the Iberian Peninsula as the cyclone is picked up
by the aforementioned trough. The new NHC track forecast has been
adjusted significantly to the north and east, especially beyond 24
hours, but still lies to the south of and is slower than the GFS and
ECMWF. Once the system moves inland, the low-level center should
dissipate over the high terrain, but a 72 hour remnant low point is
included for continuity purposes. Needless to say, confidence in the
official track forecast beyond 24 hours is quite low given the
recent shift in the models, and further adjustments will likely be
necessary.

The intensity forecast shows Leslie only slowly weakening as a
tropical cyclone during the next 24 hours due to a combination of
cool SSTs and increasing shear from the trough. However, simulated
satellite imagery and model fields suggest that Leslie will
transition to a powerful post-tropical cyclone by 36 hours, likely
still at hurricane intensity as shown by the global models.
Weakening is expected after the trough passes Leslie by, and the
mid-level circulation will likely be sheared away by strong
upper-level winds.

Leslie is expected to bring significant rain and wind impacts to
portions of Portugal and Spain by Sunday, and residents in those
areas should refer to products from their local meteorological
services for more information on these hazards.

FORECAST POSITIONS AND MAX WINDS

INIT  12/1500Z 33.0N  28.0W   75 KT  85 MPH
 12H  13/0000Z 34.2N  23.0W   70 KT  80 MPH
 24H  13/1200Z 35.4N  17.0W   65 KT  75 MPH
 36H  14/0000Z 36.0N  12.5W   65 KT  75 MPH...POST-TROPICAL
 48H  14/1200Z 36.3N   9.1W   50 KT  60 MPH...POST-TROPICAL
 72H  15/1200Z 37.0N   4.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  16/1200Z...DISSIPATED

$$
Forecaster Brennan
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