[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 061458
TCDAT3

Tropical Storm Leslie Discussion Number  41
NWS National Hurricane Center Miami FL       AL132018
1100 AM AST Sat Oct 06 2018

The central convection associated with Leslie has become better
organized this morning, with conventional satellite imagery showing
a tightly curved band and recent microwave imagery showing a
mid-level eye.  However, the microwave data also suggests the
mid-level eye is located to the southeast of the low-level center.
It is also not known whether there is an inner wind maximum
associated with this feature.  Satellite intensity estimates are
mostly in the 45-55 kt range, so the initial intensity remains 50
kt.

The initial motion is now 080/8.  Leslie is now in or near the
southern edge of the mid-latitude westerlies, and with the
assistance of a couple of shortwave troughs, these are expected to
push Leslie toward the east and southeast throughout the forecast
period.  Despite general agreement on the synoptic pattern, there is
now a large spread in the guidance toward the end of the forecast
period.  The ECMWF and UKMET show a more southward turn after 72 h,
taking Leslie well south of 30N.  The GFS, on the other hand,
shows a more eastward motion to the point where by 96 h it is 950
n mi from the UKMET forecast position.  The new forecast track
compromises between these extremes and lies near the TVCN consensus,
with the caveat that the part after 72 h is of low confidence.

Leslie should weaken some during the next 48 h or so as it crosses
an area of cooler sea surface temperatures.  After that, the track
takes the center back over warmer water at the same time when there
may be an increase in shear.  There is an increased uncertainty in
the intensity forecast caused by the track forecast uncertainties.
If Leslie moves closer to the GFS track, it will be over cooler
water and in stronger shear, while if it moves closer to the UKMET
solution it will be over warmer water and lighter shear.  Due to to
the uncertainty, only minor adjustments are made to the previous
intensity forecast.  Additional adjustments may be needed later
depending on changes in the track forecast.

Large swells generated by Leslie are expected to continue during the
next few days 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  06/1500Z 37.7N  55.8W   50 KT  60 MPH
 12H  07/0000Z 37.6N  54.1W   50 KT  60 MPH
 24H  07/1200Z 37.3N  51.5W   45 KT  50 MPH
 36H  08/0000Z 36.6N  49.0W   45 KT  50 MPH
 48H  08/1200Z 35.7N  46.5W   40 KT  45 MPH
 72H  09/1200Z 33.0N  41.5W   45 KT  50 MPH
 96H  10/1200Z 30.0N  37.0W   50 KT  60 MPH
120H  11/1200Z 29.0N  31.0W   50 KT  60 MPH

$$
Forecaster Beven
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