[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 212039
TCDAT3

TROPICAL STORM LISA DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132016
500 PM AST WED SEP 21 2016

Vertical wind shear of 15-20 kt continues to take a toll on Lisa.
The coldest convective tops have moved farther east away from the
estimated low-level center position today.  Dvorak estimates were
T2.5/3.0 from both TAFB and SAB at 18Z, and based on these, the
initial intensity has been lowered to 40 kt for this advisory. Given
that Lisa has struggled to maintain itself today, and that the SHIPS
model shows the shear increasing to 30 kt in the next 18 to 24
hours, there seems to be little opportunity left for the cyclone to
strengthen.  Given this, the new NHC intensity forecast holds Lisa
at 40 kt through 24 hours and then shows gradual weakening to
remnant low status in 3 to 4 days as the shear increases to near 40
kt and the mid-level relative humidity drops below 30 percent.  This
forecast is closest to the SHIPS and LGEM statistical-dynamical
models.

An AMSR-2 pass from GCOM-W1 from around 1430Z provided some guidance
on the center location, but it remains somewhat uncertain given the
large spread in the satellite fixes.  However, it does appear that
the center is located a little to the east of previous estimates,
and the initial motion is estimated to be 325/06.  The track
forecast scenario has not changed, as Lisa is expected to move
northwestward into a weakness in the subtropical ridge and then
recurve into the mid-latitude flow during the forecast period.
Overall, the guidance envelope has shifted eastward this cycle, and
given the eastward adjustment in the initial position, the NHC
forecast has been shifted eastward by about a degree.  The official
forecast track is close to a blend of the GFS and ECMWF and lies to
the left of multi-model consensus TVCN.

FORECAST POSITIONS AND MAX WINDS

INIT  21/2100Z 18.5N  32.5W   40 KT  45 MPH
 12H  22/0600Z 19.4N  33.3W   40 KT  45 MPH
 24H  22/1800Z 20.8N  34.7W   40 KT  45 MPH
 36H  23/0600Z 22.1N  36.0W   35 KT  40 MPH
 48H  23/1800Z 23.5N  37.2W   30 KT  35 MPH
 72H  24/1800Z 26.0N  40.0W   30 KT  35 MPH
 96H  25/1800Z 30.0N  41.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  26/1800Z 36.0N  38.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brennan

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