[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 042033
TCDAT3

Tropical Storm Leslie Discussion Number  34
NWS National Hurricane Center Miami FL       AL132018
500 PM AST Thu Oct 04 2018

Leslie has changed little in convective structure today.  Visible
imagery shows occasional appearances of an eye inside an area of
central convection, with a complex of outer bands wrapping around
this inner feature.  Infrared imagery, though, suggests that the
convection is relatively shallow.  Despite the lack of change in the
convective pattern, scatterometer data shows there have been
significant changes in the wind structure.  The strongest winds are
now in a band about 90-100 n mi from the center, with the winds in
the inner core being notably weaker.  This suggest the possibility
that Leslie is trying to undergo an eyewall replacement, albeit one
with a very large outer eyewall.  Based on the scatterometer data
and slightly decreased satellite intensity estimates, the initial
intensity is reduced to 60 kt.

There is little change to the intensity forecast philosophy, the
intensity forecast guidance, or the intensity forecast.  While the
vertical shear should remain light through the forecast period, the
forecast track takes the center away from 26C sea surface
temperatures and over 24-25C temperatures, and this should cause a
gradual weakening for the next several days.  There are major
changes to the initial and forecast wind radii based on the
scatterometer data and the analyzed initial size.

The initial motion is 355/10.  In the short term, Leslie will be
steered northward between a mid-level ridge over the central
Atlantic and a mid- to upper-level trough seen in water vapor
imagery north of Bermuda.  A decrease in forward speed should occur
from 24-36 h as the trough moves south and a second ridge develops
to the west of the tropical cyclone.  Beyond 36 h, Leslie is
expected to move eastward to east-southeastward at a faster forward
speed along the southern edge of the mid-latitude westerlies.
Overall, the new forecast track is close to the previous track
through 48 h, then a little north of the old track after that time.
However, there is an increased spread in the guidance in both the
track and the forward speed near the end of the forecast period, and
confidence is decreasing for this part of the forecast.

Large swells generated by Leslie are expected to continue during the
next few days across the southeastern coast of the United States,
Bermuda, the Bahamas, and the Greater and Lesser Antilles.  These
swells will also begin to increase near the coasts of New England
and Atlantic Canada on Friday.  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  04/2100Z 33.3N  57.5W   60 KT  70 MPH
 12H  05/0600Z 34.9N  58.0W   60 KT  70 MPH
 24H  05/1800Z 36.1N  58.2W   60 KT  70 MPH
 36H  06/0600Z 36.8N  57.5W   55 KT  65 MPH
 48H  06/1800Z 36.7N  55.9W   55 KT  65 MPH
 72H  07/1800Z 36.0N  52.5W   50 KT  60 MPH
 96H  08/1800Z 34.5N  48.5W   50 KT  60 MPH
120H  09/1800Z 32.5N  44.5W   50 KT  60 MPH

$$
Forecaster Beven
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