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Tropical Storm Lee Forecast Discussion


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Tropical Storm Lee Discussion Number  23
NWS National Hurricane Center Miami FL       AL142017
1100 PM AST Sat Sep 23 2017

An ASCAT overpass around 0014 UTC caught the western half of Lee,
and showed a maximum wind of about 40 kt.  On that basis, the
initial intensity has been increased to 45 kt, on the assumption
that the ASCAT instrument is undersampling the tiny circulation of
the tropical storm.

A WindSat overpass from 2102 UTC indicated that Lee has developed a
coherent inner-core.  In fact, the 37 GHz RGB composite from the
WindSat overpass indicated that a ring of shallow to moderate
convection surrounds the center of Lee, often a signature of a
rapidly intensifying cyclone. The NHC intensity forecast has
therefore been significantly increased for the first 48 hours of
the forecast, but falls short of explicitly forecasting rapid
intensification.  Beyond that time, most of the intensity guidance
is higher than before, and shows Lee maintaining hurricane
throughout the forecast period.  The NHC forecast is just a little
above the previous forecast at days 3-5, and close to the intensity
consensus.  It is still worth noting that small tropical cyclones
can go up or down quickly in intensity with little warning, and
confidence in the forecast is low, even with reasonable agreement
among the intensity models.

After turning almost due west earlier this evening, Lee appears to
have come to a near halt and is beginning to turn slowly toward the
southeast. Lee continues to follow the trend of the ECMWF, so the
NHC forecast has been moved farther west, closer to that model.
Although the GFS continues to insist on a east to northeast track, I
am treating it as an outlier at this time.  The remaining global
models (and the HWRF) show that Lee will gradually rotate clockwise
around a building mid-level ridge to the northwest for the next few
days before turning more toward the north at day 4.  The NHC
forecast lies between HCCA and the ECMWF, but confidence in the
track forecast is still low given the high model spread at this
time.

FORECAST POSITIONS AND MAX WINDS

INIT  24/0300Z 31.9N  50.1W   45 KT  50 MPH
 12H  24/1200Z 31.8N  50.0W   55 KT  65 MPH
 24H  25/0000Z 31.5N  49.4W   65 KT  75 MPH
 36H  25/1200Z 30.9N  48.9W   75 KT  85 MPH
 48H  26/0000Z 30.2N  48.9W   75 KT  85 MPH
 72H  27/0000Z 30.0N  50.5W   75 KT  85 MPH
 96H  28/0000Z 31.5N  52.0W   75 KT  85 MPH
120H  29/0000Z 34.5N  52.5W   70 KT  80 MPH

$$
Forecaster Zelinsky

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