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Subtropical Storm LESLIE


Subtropical Storm Leslie Discussion Number  13
NWS National Hurricane Center Miami FL       AL132018
1100 AM AST Sat Sep 29 2018

Leslie's cloud pattern has taken on a more tropical appearance
since last night.  However, the cyclone is still co-located with an
upper-level low, so its status as a subtropical cyclone is
maintained for this advisory.  The initial intensity remains 40 kt,
based on a subtropical classification of 35-40 kt from TAFB.

The global models forecast that Leslie will separate from the
upper-level low over the course of the next day or so, which should
complete its transition to a tropical cyclone. While this could
result in a short-term increase in shear over Leslie, by early next
week the cyclone will likely be located within a fairly low shear
environment. However, Leslie is expected to move very slowly by that
time, and ocean upwelling could limit or prevent further
strengthening. There is a large amount of spread in the intensity
guidance by day 5, but it is worth noting that the models most
capable of properly representing the effect of ocean cooling on
intensity, COAMPS-TC, HWRF, and HMON, all keep Leslie below
hurricane strength for the next 5 days.  The HWRF in particular
forecasts nearly 5 deg C of ocean cooling beneath the cyclone. The
NHC intensity forecast is generally a little lower than the previous
advisory, but is still near the IVCN and HCCA consensus aids at all
forecast hours. If Leslie moves more than expected, it would not be
surprising if it strengthened more than currently forecast.

Little change was made to the official track forecast.  Leslie is
still expected to move slowly southwestward for the next couple of
days, before coming to a near halt early next week.  By the
middle of the week, an approaching mid-latitude trough could steer
Leslie toward the north or northeast and allow the cyclone to start
gaining speed, however, there is a lot of spread among the global
models as to how quickly this will occur, and confidence in this
portion of the forecast is fairly low.

Large swells generated by Leslie when it was a strong extratropical
low will affect Bermuda, the east coast of the United States, and
most of the Greater and Lesser Antilles through the weekend. These
swells could cause life-threatening surf and rip currents.


INIT  29/1500Z 34.4N  50.8W   40 KT  45 MPH
 12H  30/0000Z 33.8N  51.7W   45 KT  50 MPH
 24H  30/1200Z 33.3N  52.7W   45 KT  50 MPH
 36H  01/0000Z 33.1N  53.5W   50 KT  60 MPH...TROPICAL CYCLONE
 48H  01/1200Z 32.8N  54.0W   50 KT  60 MPH
 72H  02/1200Z 31.6N  55.0W   55 KT  65 MPH
 96H  03/1200Z 31.0N  55.5W   60 KT  70 MPH
120H  04/1200Z 33.0N  55.0W   65 KT  75 MPH

Forecaster Zelinsky