Tropical Storm Leslie Discussion Number  53
NWS National Hurricane Center Miami FL       AL132018
1100 AM AST Tue Oct 09 2018

Recent Dvorak fixes and ASCAT data indicate that Leslie's maximum
winds remain around 55 kt. Although the winds have not yet
increased, the surface center of the tropical storm has become more
embedded within its cold cloud tops and several recent microwave
overpasses indicate that the cyclone is beginning to establish an
inner-core. Strengthening is therefore still expected, and Leslie is
forecast to become a hurricane by tomorrow. The tropical storm is
currently moving south-southeastward at around 11 kt, and the models
are in good agreement that a south-southeastward to southward motion
will continue for the next 24 h or so.

Beginning around 36 h, both the track and intensity forecasts become
very uncertain.  In general, most of the global models and their
ensembles indicate that Leslie will begin to accelerate toward the
east-northeast or northeast by Thursday as a mid-latitude trough
approaches from the northwest, however the timing and extent of the
interaction is still highly variable from model to model. Based on
the GFS and ECMWF ensembles, a range of possibilities exists, from
Leslie essentially merging with this trough and becoming
extratropical over the far northeast Atlantic, to Leslie interacting
with the trough very little and continuing to meander over the
central Atlantic.  There has been a significant change in the
consensus aids to show a slower track for Leslie based on recent
shifts in the deterministic models, but the NHC track forecast has
not been changed nearly as much, out of respect for continuity and
the high uncertainty in the forecast.

The low confidence in the track forecast beyond 36 h affects the
intensity forecast as well, since it is unclear what environment the
storm will be located within.  The intensity forecast is therefore
held near the intensity consensus, and still calls for steady
strengthening during the next several days, followed by weakening by
the end of the forecast period.  If Leslie moves as far east as
shown in the NHC track forecast, it would likely become a post-
tropical low by day 5, as shown explicitly in the forecast. However,
until confidence in the track increases, I can't rule out that
Leslie could remain a tropical cyclone almost indefinitely if it
continues meandering over the northern Atlantic.

FORECAST POSITIONS AND MAX WINDS

INIT  09/1500Z 31.3N  43.5W   55 KT  65 MPH
12H  10/0000Z 29.9N  42.9W   55 KT  65 MPH
24H  10/1200Z 28.5N  42.6W   60 KT  70 MPH
36H  11/0000Z 28.1N  41.7W   65 KT  75 MPH
48H  11/1200Z 28.9N  39.5W   70 KT  80 MPH
72H  12/1200Z 32.0N  31.5W   75 KT  85 MPH
96H  13/1200Z 33.5N  22.0W   65 KT  75 MPH
120H  14/1200Z 33.5N  18.0W   50 KT  60 MPH...POST-TROPICAL

$$
Forecaster Zelinsky