[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 211434
TCDAT3

TROPICAL STORM LISA DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132016
1100 AM AST WED SEP 21 2016

The cloud pattern of Lisa has not changed much since the previous
advisory.  A 0911 UTC SSMIS image suggested that the low-level
center was located on the western edge of the central convection.
The 12Z Dvorak Data-T numbers from SAB and TAFB decreased and a
partial ASCAT-B pass from 1115 UTC only showed 30-35 kt winds in the
northeastern quadrant.  However, the initial intensity is held at 45
kt given the lack of clear evidence of weakening and in agreement
with the the latest Dvorak CI numbers of T3.0/45 kt.  There is only
a small opportunity for the cyclone to strengthen before the shear
increases even further in 24 to 36 hours.  Weakening is expected
after that time, and later in the period, as the mid-level
environment becomes quite dry, the cyclone should weaken to a
remnant low.  The new NHC intensity forecast is similar to the
previous one and is near the middle of the guidance in the first 36
hours and then is near or below the weaker LGEM solution after that
time.

The initial motion estimate is a somewhat uncertain 320/07, given
the lack of confidence in the location of the center.  Lisa will
move northwestward during the next 72 hours into a weakness in the
subtropical ridge over the eastern Atlantic, and then recurve into
the mid-latitude westerlies on days 4 and 5.  The global models are
in generally good agreement on this scenario, with the ECMWF lying
on the left side of the guidance cluster and the GFS shifting to the
right this cycle.  The new NHC track forecast is an update of the
previous one but has been adjusted for the initial position and
motion.  This forecast is near a blend of the latest GFS and ECMWF
tracks and is well to the left of the GFDL and HWRF models, which
lie nearly 200 n mi east of the rest of the guidance at days 3 and
4.

FORECAST POSITIONS AND MAX WINDS

INIT  21/1500Z 18.0N  32.5W   45 KT  50 MPH
 12H  22/0000Z 18.6N  33.4W   50 KT  60 MPH
 24H  22/1200Z 19.7N  34.9W   45 KT  50 MPH
 36H  23/0000Z 20.9N  36.5W   45 KT  50 MPH
 48H  23/1200Z 22.3N  38.0W   40 KT  45 MPH
 72H  24/1200Z 25.0N  41.0W   30 KT  35 MPH
 96H  25/1200Z 28.5N  43.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  26/1200Z 34.0N  41.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brennan
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