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Tropical Storm LEE (Text)


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Tropical Storm Lee Discussion Number  19
NWS National Hurricane Center Miami FL       AL142017
1100 PM AST Fri Sep 22 2017

Several microwave overpasses between 2100 and 2200 UTC indicated
that Lee was becoming better organized, at least at the mid-levels.
In particular, a WindSat overpass near 21Z indicated that a
mid-level eye was already forming.  Since that time, however, cloud
tops have warmed, the CDO has shrunk, and a GPM overpass around 0100
UTC showed that most of the convection is currently confined to the
southeast semicircle of the tropical storm. The UW-CIMSS ADT
supports an intensity of 35 kt, and the TAFB Dvorak analyst
indicated that the subjective classification would have been higher,
if the technique wasn't constrained by the fact that classifications
on Lee only recently restarted.  Based on these data, the initial
intensity has been increased to 35 kt.

The intensity forecast for Lee is highly uncertain.  The tropical
storm is very small, and small cyclones often quickly strengthen or
weaken.  Furthermore, Lee is small enough that some of our models
(and many of our observing platforms) may have trouble resolving the
inner core of the storm.  Given the current convective state of Lee,
significant strengthening in the short term seems unlikely.
However, the cyclone is expected to be in a fairly unstable, low
shear environment for at least the next 3 days, so it is possible
that rapid intensification could occur at some time during that
period.  On the other hand, I can't rule out that the cyclone could
dissipate entirely, as depicted by the GFS, within a couple days.
For now, my forecast is closest to the HWRF for the first 72 h,
since that model tends to do well in low-shear environments and
should have sufficient resolution to model Lee's core.  After that
time, the forecast is close to the HCCA and IVCN intensity consensus
models.

Lee has continued to move north around 6 kt.  Little change has been
made to the track forecast, and Lee is still forecast to move around
a subtropical ridge for the next 72 h.  At days 4 and 5, a ridge
building between Lee and Maria to the west should cause a turn more
toward the south, as long as Lee is sufficiently deep to be steered
by that feature.  The forecast continues to be close to the ECMWF,
since it is still the global model with the strongest representation
of Lee, in line with the NHC forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  23/0300Z 31.5N  49.0W   35 KT  40 MPH
 12H  23/1200Z 32.2N  48.5W   40 KT  45 MPH
 24H  24/0000Z 32.5N  47.8W   45 KT  50 MPH
 36H  24/1200Z 32.4N  46.6W   50 KT  60 MPH
 48H  25/0000Z 32.1N  45.2W   60 KT  70 MPH
 72H  26/0000Z 31.3N  43.1W   75 KT  85 MPH
 96H  27/0000Z 30.0N  42.5W   75 KT  85 MPH
120H  28/0000Z 29.5N  43.5W   65 KT  75 MPH

$$
Forecaster Zelinsky

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Page last modified: Sunday, 17-Dec-2017 12:09:35 UTC